Neurophysiological Correlates of Colour Induction on White Surfaces

The European Journal of Neuroscience. Oct, 1992  |  Pubmed ID: 12106413

Coloured light surrounding a white surface of about equal luminance makes the white surface appear illuminated with an unsaturated light of the complementary colour. In an attempt to discover the neurophysiological basis of such colour induction, we recorded from spectrally opponent cells of the parvocellular layers of the lateral geniculate nucleus (P-LGN) of anaesthetized macaques. Only cells with wide-band (W) spectral sensitivity in the short (S) or long wavelength (L) part of the spectrum (WS, WL) are excited by white spots of light centred on their receptive field. Cells with narrow-band (N) spectral sensitivity (NS, NL) and light-inhibited (LI) cells are inhibited by white light. Therefore, it is likely that the code for white is contained in a balanced excitation of the W cells. The effects of continuous illumination of remote surrounds with different wavelengths on the responses to achromatic light stimuli were investigated. Responses [on minus maintained discharge rate (MDR) or on-minus-off] were determined for white spots (1 - 3 degrees diameter) flashed on the receptive field centre, presented either alone or in the presence of an annular surround of equal luminance (inner diameter 5 degrees; outer diameter 20 degrees ). During red surround illumination the responses of WL cells to white spots tended to be reduced as were those of WS cells during blue surround illumination. Surround illumination with the opponent colour had more variable effects, neither WS nor WL cells showing a significant alteration of their mean response to white during surround illumination with opponent light. Response alterations were to a large extent due to changes in MDR, which increased in WS cells during blue surround illumination and in WL cells during red surround illumination. It is argued that the surround effects on centre responses are due to intraocular stray light rather than lateral connections in the retina. The surround effects also depended to some extent on the size of the test spot. LI cells and the very rare parvocellular panchromatic on-cells showed no chromatic response changes during coloured surround illumination. Inasmuch as the excitation of WS cells, either alone or in combination with NS cell activation, is involved in coding for green and blue, and that of WL cells, in combination with NL cell activation, is involved in coding for red and yellow in perception, the shift of excitation towards one or the other W cell group indicates relatively more red or green signals in the white response, consistent with and in the same direction as colour induction. In addition, the summed population response of WS and WL cells is decreased during surround illumination with any colour including white. This is related to brightness decrease during surround illumination in perception.

Attention Modulates Responses in the Human Lateral Geniculate Nucleus

Nature Neuroscience. Nov, 2002  |  Pubmed ID: 12379861

Attentional mechanisms are important for selecting relevant information and filtering out irrelevant information from cluttered visual scenes. Selective attention has previously been shown to affect neural activity in both extrastriate and striate visual cortex. Here, evidence from functional brain imaging shows that attentional response modulation is not confined to cortical processing, but can occur as early as the thalamic level. We found that attention modulated neural activity in the human lateral geniculate nucleus (LGN) in several ways: it enhanced neural responses to attended stimuli, attenuated responses to ignored stimuli and increased baseline activity in the absence of visual stimulation. The LGN, traditionally viewed as the gateway to visual cortex, may also serve as a 'gatekeeper' in controlling attentional response gain.

Attentional Control of the Processing of Neural and Emotional Stimuli

Brain Research. Cognitive Brain Research. Dec, 2002  |  Pubmed ID: 12433381

A typical scene contains many different objects that compete for neural representation due to the limited processing capacity of the visual system. At the neural level, competition among multiple stimuli is evidenced by the mutual suppression of their visually evoked responses and occurs most strongly at the level of the receptive field. The competition among multiple objects can be biased by both bottom-up sensory-driven mechanisms and top-down influences, such as selective attention. Functional brain imaging studies reveal that biasing signals due to selective attention can modulate neural activity in visual cortex not only in the presence but also in the absence of visual stimulation. Although the competition among stimuli for representation is ultimately resolved within visual cortex, the source of top-down biasing signals likely derives from a distributed network of areas in frontal and parietal cortex. Competition suggests that once attentional resources are depleted, no further processing is possible. Yet, existing data suggest that emotional stimuli activate brain regions "automatically," largely immune from attentional control. We tested the alternative possibility, namely, that the neural processing of stimuli with emotional content is not automatic and instead requires some degree of attention. Our results revealed that, contrary to the prevailing view, all brain regions responding differentially to emotional faces, including the amygdala, did so only when sufficient attentional resources were available to process the faces. Thus, similar to the processing of other stimulus categories, the processing of facial expression is under top-down control.

Neuroimaging Studies of Attention: from Modulation of Sensory Processing to Top-down Control

The Journal of Neuroscience : the Official Journal of the Society for Neuroscience. May, 2003  |  Pubmed ID: 12764083

Multidisciplinary Rehabilitation Versus Usual Care for Chronic Low Back Pain in the Community: Effects on Quality of Life

The Spine Journal : Official Journal of the North American Spine Society. Jul-Aug, 2003  |  Pubmed ID: 14589185

Multidisciplinary biopsychosocial rehabilitation has been shown in controlled studies to improve pain and function in patients with chronic back pain. However, specialized back pain rehabilitation centers are rare and only a few patients can participate on this therapy. Implementation of multidisciplinary rehabilitation services in community medicine may enhance both early availability and treatment capacity for comprehensive back pain rehabilitation.

Push-pull Mechanism of Selective Attention in Human Extrastriate Cortex

Journal of Neurophysiology. Jul, 2004  |  Pubmed ID: 14973320

Selective attention operates in visual cortex by facilitating processing of selected stimuli and by filtering out unwanted information from nearby distracters over circumscribed regions of visual space. The neural representation of unattended stimuli outside this focus of attention is less well understood. We studied the neural fate of unattended stimuli using functional magnetic resonance imaging by dissociating the activity evoked by attended (target) stimuli presented to the periphery of a visual hemifield and unattended (distracter) stimuli presented simultaneously to a corresponding location of the contralateral hemifield. Subjects covertly directed attention to a series of target stimuli and performed either a low or a high attentional-load search task on a stream of otherwise identical stimuli. With this task, target-search-related activity increased with increasing attentional load, whereas distracter-related activity decreased with increasing load in areas V4 and TEO but not in early areas V1 and V2. This finding presents evidence for a load-dependent push-pull mechanism of selective attention that operates over large portions of the visual field at intermediate processing stages. This mechanism appeared to be controlled by a distributed frontoparietal network of brain areas that reflected processes related to target selection during spatially directed attention.

Unstable Endobronchial Intubation in a Cat Undergoing Tracheal Laceration Repair

Veterinary Anaesthesia and Analgesia. Jul, 2004  |  Pubmed ID: 15268695

A peri-carinal tracheal laceration was produced in a 11-year-old cat during tracheal intubation. Before reconstructive surgery began, the leak was bypassed with an endobronchial tube positioned using endoscopy and direct vision. However, single-lung ventilation could not be sustained because the tube became dislodged and could not be repositioned. Consequently, surgery was completed with periods of intermittent apnoea interspersed with manually controlled hyperventilation. Cardiovascular variables were stable during anaesthesia and no signs of hypoxia were detected. The difficulties in maintaining endobronchial tube position resulted from the animal's small size relative to the dimensions of the endotracheal tube.

Retinotopic Organization and Functional Subdivisions of the Human Lateral Geniculate Nucleus: a High-resolution Functional Magnetic Resonance Imaging Study

The Journal of Neuroscience : the Official Journal of the Society for Neuroscience. Oct, 2004  |  Pubmed ID: 15483116

Functional magnetic resonance imaging (fMRI) has provided intriguing insights into the topography and functional organization of visual cortical areas in the human brain. However, little is known about the functional anatomy of subcortical nuclei. Here, we used high-resolution fMRI (1.5 x 1.5 x 2 mm3) at 3 tesla to investigate the retinotopic organization of the human lateral geniculate nucleus (LGN). The central 15 degrees of the visual field were mapped using periodic flickering checkerboard stimuli that evoked a traveling wave of activity. The contralateral visual hemifield was represented with the lower field in the medial-superior portion and the upper field in the lateral-inferior portion of each LGN. The horizontal meridian was significantly overrepresented relative to the vertical meridian. The fovea was represented in posterior and superior portions, with increasing eccentricities represented more anteriorly. The magnification of the fovea relative to the periphery was similar to that described for human primary visual cortex. The magnocellular regions of the LGN were distinguished based on their sensitivity to low stimulus contrast and tended to be located in its inferior and medial portions. Our results demonstrate striking similarities in the topographic organization of the macaque and human LGN and support accounts of a constant magnification from the retina through the cortex in both species.

Functional Imaging of the Human Lateral Geniculate Nucleus and Pulvinar

Journal of Neurophysiology. Jan, 2004  |  Pubmed ID: 13679404

In the human brain, little is known about the functional anatomy and response properties of subcortical nuclei containing visual maps such as the lateral geniculate nucleus (LGN) and the pulvinar. Using functional magnetic resonance imaging (fMRI) at 3 tesla (T), collective responses of neural populations in the LGN were measured as a function of stimulus contrast and flicker reversal rate and compared with those obtained in visual cortex. Flickering checkerboard stimuli presented in alternation to the right and left hemifields reliably activated the LGN. The peak of the LGN activation was found to be on average within +/-2 mm of the anatomical location of the LGN, as identified on high-resolution structural images. In all visual areas except the middle temporal (MT), fMRI responses increased monotonically with stimulus contrast. In the LGN, the dynamic response range of the contrast function was larger and contrast gain was lower than in the cortex. Contrast sensitivity was lowest in the LGN and V1 and increased gradually in extrastriate cortex. In area MT, responses were saturated at 4% contrast. Response modulation by changes in flicker rate was similar in the LGN and V1 and occurred mainly in the frequency range between 0.5 and 7.5 Hz; in contrast, in extrastriate areas V4, V3A, and MT, responses were modulated mainly in the frequency range between 7.5 and 20 Hz. In the human pulvinar, no activations were obtained with the experimental designs used to probe response properties of the LGN. However, regions in the mediodorsal right and left pulvinar were found to be consistently activated by bilaterally presented flickering checkerboard stimuli, when subjects attended to the stimuli. Taken together, our results demonstrate that fMRI at 3 T can be used effectively to study thalamocortical circuits in the human brain.

Visual Attention As a Multilevel Selection Process

Cognitive, Affective & Behavioral Neuroscience. Dec, 2004  |  Pubmed ID: 15849892

Natural visual scenes are cluttered and contain many different objects that cannot all be processed simultaneously. Therefore, attentional mechanisms are needed to select relevant and to filter out irrelevant information. Evidence from functional brain imaging reveals that attention operates at various processing levels within the visual system and beyond. First, the lateral geniculate nucleus appears to be the first stage in the processing of visual information that is modulated by attention, consistent with the idea that it may play an important role as an early gatekeeper in controlling neural gain. Second, areas at intermediate cortical-processing levels, such as V4 and TEO, appear to be important sites at which attention filters out unwanted information by means of receptive field mechanisms. Third, the attention mechanisms that operate in the visual system appear to be controlled by a distributed network of higher order areas in the frontal and parietal cortex, which generate top-down signals that are transmitted via feedback connections to the visual system. And fourth, the pulvinar of the thalamus may operate by integrating and coordinating attentional functions in concert with the fronto-parietal network, although much needs to be learned about its functional properties. The overall view that emerges from the studies reviewed in this article is that neural mechanisms of selective attention operate at multiple stages in the visual system and beyond and are determined by the visual processing capabilities of each stage. In this respect, attention can be considered in terms of a multilevel selection process.

Representations of Faces and Body Parts in Macaque Temporal Cortex: a Functional MRI Study

Proceedings of the National Academy of Sciences of the United States of America. May, 2005  |  Pubmed ID: 15860578

Human neuroimaging studies suggest that areas in temporal cortex respond preferentially to certain biologically relevant stimulus categories such as faces and bodies. Single-cell studies in monkeys have reported cells in inferior temporal cortex that respond selectively to faces, hands, and bodies but provide little evidence of large clusters of category-specific cells that would form "areas." We probed the category selectivity of macaque temporal cortex for representations of monkey faces and monkey body parts relative to man-made objects using functional MRI in animals trained to fixate. Two face-selective areas were activated bilaterally in the posterior and anterior superior temporal sulcus exhibiting different degrees of category selectivity. The posterior face area was more extensively activated in the right hemisphere than in the left hemisphere. Immediately adjacent to the face areas, regions were activated bilaterally responding preferentially to body parts. Our findings suggest a category-selective organization for faces and body parts in macaque temporal cortex.

Closed System Anaesthesia in Dogs Using Liquid Sevoflurane Injection; Evaluation of the Square-root-of-time Model and the Influence of CO2 Absorbent

Veterinary Anaesthesia and Analgesia. May, 2005  |  Pubmed ID: 15877663

To determine whether predictable alveolar concentrations of sevoflurane are reliably produced in dogs when liquid sevoflurane is injected into closed circuit breathing systems, as calculated by Lowe's square-root-of-time anaesthetic uptake model, and to confirm the validity of the model using soda lime and calcium hydroxide lime.

Visual Responses of the Human Superior Colliculus: a High-resolution Functional Magnetic Resonance Imaging Study

Journal of Neurophysiology. Oct, 2005  |  Pubmed ID: 15944234

The superior colliculus (SC) is a multimodal laminar structure located on the roof of the brain stem. The SC is a key structure in a distributed network of areas that mediate saccadic eye movements and shifts of attention across the visual field and has been extensively studied in nonhuman primates. In humans, it has proven difficult to study the SC with functional MRI (fMRI) because of its small size, deep location, and proximity to pulsating vascular structures. Here, we performed a series of high-resolution fMRI studies at 3 T to investigate basic visual response properties of the SC. The retinotopic organization of the SC was determined using the traveling wave method with flickering checkerboard stimuli presented at different polar angles and eccentricities. SC activations were confined to stimulation of the contralateral hemifield. Although a detailed retinotopic map was not observed, across subjects, the upper and lower visual fields were represented medially and laterally, respectively. Responses were dominantly evoked by stimuli presented along the horizontal meridian of the visual field. We also measured the sensitivity of the SC to luminance contrast, which has not been previously reported in primates. SC responses were nearly saturated by low contrast stimuli and showed only small response modulation with higher contrast stimuli, indicating high sensitivity to stimulus contrast. Responsiveness to stimulus motion in the SC was shown by robust activations evoked by moving versus static dot stimuli that could not be attributed to eye movements. The responses to contrast and motion stimuli were compared with those in the human lateral geniculate nucleus. Our results provide first insights into basic visual responses of the human SC and show the feasibility of studying subcortical structures using high-resolution fMRI.

The Use of Sarmazenil in the Treatment of a Moxidectin Intoxication in a Foal

Journal of Veterinary Internal Medicine / American College of Veterinary Internal Medicine. May-Jun, 2005  |  Pubmed ID: 15954550

Stimulus Context Modulates Competition in Human Extrastriate Cortex

Nature Neuroscience. Aug, 2005  |  Pubmed ID: 16007082

When multiple stimuli appear simultaneously in the visual field, they are not processed independently, but rather interact in a mutually suppressive way, suggesting that they compete for neural representation in visual cortex. The biased competition model of selective attention predicts that the competition can be influenced by both top-down and bottom-up mechanisms. Directed attention has been shown to bias competition in favor of the attended stimulus in extrastriate cortex. Here, we show that suppressive interactions among multiple stimuli are eliminated in extrastriate cortex when they are presented in the context of pop-out displays, in which a single item differs from the others, but not in heterogeneous displays, in which all items differ from each other. The pop-out effects seemed to originate in early visual cortex and were independent of attentional top-down control, suggesting that stimulus context may provide a powerful influence on neural competition in human visual cortex.

Symmetry Perception in Humans and Macaques

Trends in Cognitive Sciences. Sep, 2005  |  Pubmed ID: 16081313

The human ability to detect symmetry has been a topic of interest to psychologists and philosophers since the 19th century, yet surprisingly little is known about the neural basis of symmetry perception. In a recent fMRI study, Sasaki and colleagues begin to remedy this situation. By identifying the neural structures that respond to symmetry in both humans and macaques, the authors lay the groundwork for understanding the neural mechanisms underlying symmetry perception.

Methods for Functional Magnetic Resonance Imaging in Normal and Lesioned Behaving Monkeys

Journal of Neuroscience Methods. Apr, 2005  |  Pubmed ID: 15814151

Methods for performing functional magnetic resonance imaging (fMRI) studies in behaving and lesioned monkeys using a human MR scanner are reported. Materials for head implant surgery were selected based on tests for magnetic susceptibility. A primate chair with a rigid head fixation system and a mock scanner environment for training were developed. To perform controlled visual studies, monkeys were trained to maintain fixation for several minutes using a novel training technique that utilized continuous juice rewards. A surface coil was used to acquire anatomical and functional images in four monkeys, one with a partial lesion of striate cortex. High-resolution anatomical images were used after non-uniform intensity correction to create cortical surface reconstructions of both lesioned and normal hemispheres. Our methods were confirmed in two visual experiments, in which functional activations were obtained during both free viewing and fixation conditions. In one experiment, face-selective activity was found in the fundus and banks of the superior temporal sulcus and the middle temporal gyrus in monkeys viewing pictures of faces and objects while maintaining fixation. In a second experiment, regions in occipital, parietal, and frontal cortex were activated in lesioned and normal animals viewing a cartoon movie. Importantly, in the animal with the striate lesion, fMRI signals were obtained in the immediate vicinity of the lesion. Our results extend those previously reported by providing a detailed account of the technique and by demonstrating the feasibility of fMRI in monkeys with lesions.

Quantitative Investigation of Connections of the Prefrontal Cortex in the Human and Macaque Using Probabilistic Diffusion Tractography

The Journal of Neuroscience : the Official Journal of the Society for Neuroscience. Sep, 2005  |  Pubmed ID: 16192375

The functions of prefrontal cortex (PFC) areas are constrained by their anatomical connections. There is little quantitative information about human PFC connections, and, instead, our knowledge of primate PFC connections is derived from tracing studies in macaques. The connections of subcortical areas, in which white matter penetration and hence diffusion anisotropy are greatest, can be studied with diffusion-weighted imaging (DWI) tractography. We therefore used DWI tractography in four macaque and 10 human hemispheres to compare the connections of PFC regions with nine subcortical regions, including several fascicles and several subcortical nuclei. A distinct connection pattern was identified for each PFC and each subcortical region. Because some of the fascicles contained connections with posterior cortical areas, it was also possible to draw inferences about PFC connection patterns with posterior cortical areas. Notably, it was possible to identify similar circuits centered on comparable PFC regions in both species; PFC regions probably engage in similar patterns of regionally specific functional interaction with other brain areas in both species. In the case of one area traditionally assigned to the human PFC, the pars opercularis, the distribution of connections was not reminiscent of any macaque PFC region but, instead, resembled the pattern for macaque ventral premotor area. Some limitations to the DWI approach were apparent; the high diffusion anisotropy in the corpus callosum made it difficult to compare connection probability values in the adjacent cingulate region.

Neural Correlates of Binocular Rivalry in the Human Lateral Geniculate Nucleus

Nature Neuroscience. Nov, 2005  |  Pubmed ID: 16234812

When dissimilar images are presented to the two eyes, they compete for perceptual dominance so that only one image is visible at a time while the other one is suppressed. Neural correlates of such binocular rivalry have been found at multiple stages of visual processing, including striate and extrastriate visual cortex. However, little is known about the role of subcortical processing during binocular rivalry. Here we used fMRI to measure neural activity in the human LGN while subjects viewed contrast-modulated gratings presented dichoptically. Neural activity in the LGN correlated strongly with the subjects' reported percepts, such that activity increased when a high-contrast grating was perceived and decreased when a low-contrast grating was perceived. Our results provide evidence for a functional role of the LGN in binocular rivalry and suggest that the LGN, traditionally viewed as the gateway to the visual cortex, may be an early gatekeeper of visual awareness.

Cardiopulmonary Effects of Dexmedetomidine in Sevoflurane-anesthetized Sheep with and Without Nitric Oxide Inhalation

American Journal of Veterinary Research. Sep, 2005  |  Pubmed ID: 16261821

To determine whether inhaled nitric oxide (NO) prevents pulmonary hypertension and improves oxygenation after i.v. administration of a bolus of dexmedetomidine in anesthetized sheep.

Total Intravenous Anaesthesia in Horses Using Medetomidine and Propofol

Veterinary Anaesthesia and Analgesia. Nov, 2005  |  Pubmed ID: 16297044

To examine the clinical suitability of medetomidine-propofol infusions for total intravenous anaesthesia in horses.

Comparison of Two Pre-anaesthetic Medetomidine Doses in Isoflurane Anaesthetized Sheep

Veterinary Anaesthesia and Analgesia. Jan, 2006  |  Pubmed ID: 16412127

To compare the sedative, anaesthetic-sparing and arterial blood-gas effects of two medetomidine (MED) doses used as pre-anaesthetic medication in sheep undergoing experimental orthopaedic surgery.

Effects of an Alveolar Recruitment Maneuver on Cardiovascular and Respiratory Parameters During Total Intravenous Anesthesia in Ponies

American Journal of Veterinary Research. Jan, 2006  |  Pubmed ID: 16426225

To evaluate pulmonary and cardiovascular effects of a recruitment maneuver (RM) combined with positive end-expiratory pressure (PEEP) during total intravenous anesthesia in ponies.

Antibiotic Susceptibility Patterns and Resistance Genes of Starter Cultures and Probiotic Bacteria Used in Food

Systematic and Applied Microbiology. Mar, 2006  |  Pubmed ID: 16464696

A survey of starter and probiotic cultures was carried out to determine the current antibiotic resistance situation in microbial food additives in Switzerland. Two hundred isolates from 90 different sources were typed by molecular and other methods to belong to the genera Lactobacillus (74 samples), Staphylococcus (33 samples), Bifidobacterium (6 samples), Pediococcus (5 samples), or were categorized as lactococci or streptococci (82 samples). They were screened for phenotypic resistances to 20 antibiotics by the disk diffusion method. Twenty-seven isolates exhibiting resistances that are not an intrinsic feature of the respective genera were further analyzed by microarray hybridization as a tool to trace back phenotypic resistances to specific genetic determinants. Their presence was finally verified by PCR amplification or Southern hybridization. These studies resulted in the detection of the tetracycline resistance gene tet(K) in 5 Staphylococcus isolates used as meat starter cultures, the tetracycline resistance gene tet(W) in the probiotic cultures Bifidobacterium lactis DSM 10140 and Lactobacillus reuteri SD 2112 (residing on a plasmid), and the lincosamide resistance gene lnu(A) (formerly linA) in L. reuteri SD 2112.

A2-agonists in Sheep: a Review

Veterinary Anaesthesia and Analgesia. Mar, 2006  |  Pubmed ID: 16475998

To review the use and adverse effects of alpha(2)-agonists in sheep.

Beyond a Relay Nucleus: Neuroimaging Views on the Human LGN

Progress in Brain Research. , 2006  |  Pubmed ID: 17027384

The lateral geniculate nucleus (LGN) is the thalamic station in the retinocortical projection and has traditionally been viewed as the gateway for sensory information to enter the cortex. Here, we review recent studies of the human LGN that have investigated the retinotopic organization, physiologic response properties, and modulation of neural activity by selective attention and by visual awareness in a binocular rivalry paradigm. In the retinotopy studies, we found that the contralateral visual field was represented with the lower field in the medial-superior portion and the upper field in the lateral-inferior portion of each LGN. The fovea was represented in posterior and superior portions, with increasing eccentricities represented more anteriorly. Functional MRI responses increased monotonically with stimulus contrast in the LGN and in visual cortical areas. In the LGN, the dynamic response range of the contrast function was larger and contrast gain was lower than in the cortex. In our attention studies, we found that directed attention to a spatial location modulated neural activity in the LGN in several ways: it enhanced neural responses to attended stimuli, attenuated responses to ignored stimuli, and increased baseline activity in the absence of visual stimulation. Furthermore, we showed in a binocular rivalry paradigm that neural activity in the LGN correlated strongly with the subjects' reported percepts. The overall view that emerges from these studies is that the human LGN plays a role in perception and cognition far beyond that of a relay nucleus and, rather, needs to be considered as an early gatekeeper in the control of visual attention and awareness.

The Evolution of Prefrontal Inputs to the Cortico-pontine System: Diffusion Imaging Evidence from Macaque Monkeys and Humans

Cerebral Cortex (New York, N.Y. : 1991). Jun, 2006  |  Pubmed ID: 16120793

The cortico-ponto-cerebellar system is one of the largest projection systems in the primate brain, but in the human brain the nature of the information processing in this system remains elusive. Determining the areas of the cerebral cortex which contribute projections to this system will allow us to better understand information processing within it. Information from the cerebral cortex is conveyed to the cerebellum by topographically arranged fibres in the cerebral peduncle - an important fibre system in which all cortical outputs spatially converge on their way to the cerebellum via the pontine nuclei. Little is known of their anatomical organization in the human brain. New in vivo diffusion imaging and probabilistic tractography methods now offer a way in which input tracts in the cerebral peduncle can be characterized in detail. Here we use these methods to contrast their organization in humans and macaque monkeys. We confirm the dominant contribution of the cortical motor areas to the macaque monkey cerebral peduncle. However, we also present novel anatomical evidence for a relatively large prefrontal contribution to the human cortico-ponto-cerebellar system in the cerebral peduncle. These findings suggest the selective evolution of prefrontal inputs to the human cortico-ponto-cerebellar system.

Evaluation of a Combined Transcutaneous Carbon Dioxide Pressure and Pulse Oximetry Sensor in Adult Sheep and Dogs

American Journal of Veterinary Research. Mar, 2007  |  Pubmed ID: 17331015

To evaluate a combined transcutaneous carbon dioxide pressure (tcPCO(2)) and pulse oximetry sensor in sheep and dogs.

Topographic Maps in Human Frontal Cortex Revealed in Memory-guided Saccade and Spatial Working-memory Tasks

Journal of Neurophysiology. May, 2007  |  Pubmed ID: 17360822

We used fMRI at 3 Tesla and improved spatial resolution (2 x 2 x 2 mm(3)) to investigate topographic organization in human frontal cortex using memory-guided response tasks performed at 8 or 12 peripheral locations arranged clockwise around a central fixation point. The tasks required the location of a peripheral target to be remembered for several seconds after which the subjects either made a saccade to the remembered location (memory-guided saccade task) or judged whether a test stimulus appeared in the same or a slightly different location by button press (spatial working-memory task). With these tasks, we found two topographic maps in each hemisphere, one in the superior branch of precentral cortex and caudalmost part of the superior frontal sulcus, in the region of the human frontal eye field, and a second in the inferior branch of precentral cortex and caudalmost part of the inferior frontal sulcus, both of which greatly overlapped with activations evoked by visually guided saccades. In each map, activated voxels coded for saccade directions and memorized locations predominantly in the contralateral hemifield with neighboring saccade directions and memorized locations represented in adjacent locations of the map. Particular saccade directions or memorized locations were often represented in multiple locations of the map. The topographic activation patterns showed individual variability from subject to subject but were reproducible within subjects. Notably, only saccade-related activation, but no topographic organization, was found in the region of the human supplementary eye field in dorsomedial prefrontal cortex. Together these results show that topographic organization can be revealed outside sensory cortical areas using more complex behavioral tasks.

Neuroscience: Unconscious Networking

Nature. May, 2007  |  Pubmed ID: 17476253

Evaluation of the I-STAT Portable Clinical Analyzer in Chickens (Gallus Gallus)

Journal of Veterinary Diagnostic Investigation : Official Publication of the American Association of Veterinary Laboratory Diagnosticians, Inc. Jul, 2007  |  Pubmed ID: 17609347

The i-STAT portable clinical analyzer (PCA) was evaluated for performance in avian species. With the EG7+ cartridge, which provided results for hydrogen ion concentration, oxygen tension, carbon dioxide tension, sodium, potassium, ionized calcium, hematocrit, and various calculated parameters, analytical accuracy and precision were tested by comparing obtained values to those of established traditional blood gas and chemistry analyzers. Deming's regression and bias plots were used to compare i-STAT results with those obtained by laboratory professionals using benchtop analyzers. The reliability of the i-STAT PCA with EG7+ cartridges was good, with 0-5.7% system failures in measured values. Regression statistics were good for all blood gas analytes and acceptable for electrolytes and calculated parameters, except for potassium and base excess, for which the regression data or the discrepancy between the methods was too large. The system was reliable and easy to use and had an overall acceptable accuracy in avian species. These features, together with portability and small required blood volumes, make the i-STAT suitable for point-of-care use in critical avian patients, although single values require careful interpretation.

Mechanisms of Feature- and Space-based Attention: Response Modulation and Baseline Increases

Journal of Neurophysiology. Oct, 2007  |  Pubmed ID: 17671104

Selective attention modulates neural activity in the visual system both in the presence and in the absence of visual stimuli. When subjects direct attention to a particular location in a visual scene in anticipation of the stimulus onset, there is an increase in baseline activity. How do such baseline increases relate to the attentional modulation of stimulus-driven activity? Using functional magnetic resonance imaging, we demonstrate that baseline increases related to the expectation of motion or color stimuli at a peripheral target location do not predict the modulation of neural responses evoked by these stimuli when attended. In areas such as MT and TEO that were more effectively activated by one stimulus type than the other, attentional modulation of visually evoked activity depended on the stimulus preference of a visual area and was stronger for the effective than for the noneffective stimulus. In contrast, baseline increases did not reflect the stimulus preference of a visual area. Rather, these signals were shown to be spatially specific and appeared to be dominated by the location information and not by the feature information of the cue with the experimental paradigms under study. These findings provide evidence that baseline increases in visual cortex during cue periods do not reflect the activation of a memory template that includes particular stimulus properties of the expected target, but rather carry information about the location of an expected target stimulus. In addition, when the stimulus contained both color and motion, an object-based attention effect was observed, with significant attentional modulation in the area that responded preferentially to the unattended feature.

Out of the Spotlight: Face to Face with Attention

Nature Neuroscience. Nov, 2007  |  Pubmed ID: 17965650

Hyaluronan Induces the Selective Accumulation of Matrix- and Cell-associated Proteoglycans by Mesangial Cells

The American Journal of Pathology. Dec, 2007  |  Pubmed ID: 17974600

Mesangial cells (MCs) are essential for normal renal function through the synthesis of their own extracellular matrix, which forms the structural support of the renal glomerulus. In many renal diseases this matrix is reorganized in response to a variety of cytokines and growth factors. This study examines proteoglycan and hyaluronan (HA) synthesis by MCs triggered by proinflammatory agents and investigates the effect of an exogenous HA matrix on matrix synthesis by MCs. Metabolic labeling, ion exchange and size exclusion chromatography, Western blotting, and immunocytochemistry were used to identify changes in matrix accumulation. When incubated with interleukin-1, platelet-derived growth factor, or fetal calf serum, MCs initiated rapid HA synthesis associated with the up-regulation of HA synthase-2 and increased the synthesis of versican, perlecan, and decorin/biglycan. HA was both released into the medium and incorporated into extensive pericellular coats. Adding exogenous HA to unstimulated cells that had undetectable pericellular coats of HA selectively reduced perlecan and versican turnover, whereas other proteoglycans were unaffected. These results suggest that high levels of HA in the mesangium in disease is a mechanism controlling the accumulation of specific mesangial matrix components. HA may thus be an attractive target for therapeutic intervention.

Stimulus Similarity Modulates Competitive Interactions in Human Visual Cortex

Journal of Vision. , 2007  |  Pubmed ID: 18217834

When multiple visual stimuli are simultaneously presented in a neuron's receptive field, they often interact with each other by mutually suppressing their visually evoked responses, suggesting that multiple stimuli present at the same time in the visual field compete for neural representation. Previous research has shown that these suppressive interactions can be biased by top-down influences such as spatially directed attention, as well as by the bottom-up factor of visual salience. Using fMRI, we asked whether competitive interactions might also be modulated by other bottom-up factors and tested the effects of stimulus similarity. Specifically, we found that suppressive interactions in area V4, measured by comparing activity evoked by simultaneous (potentially competing) and sequential (noncompeting) presentations, were reduced when four items were identical relative to when the four items differed in color and orientation. Such a result is consistent with the prediction that competition is more likely to occur between groups than within a group.

Complex Organization of Human Primary Motor Cortex: a High-resolution FMRI Study

Journal of Neurophysiology. Oct, 2008  |  Pubmed ID: 18684903

A traditional view of the human motor cortex is that it contains an overlapping sequence of body part representations from the tongue in a ventral location to the foot in a dorsal location. In this study, high-resolution functional MRI (1.5x1.5x2 mm) was used to examine the somatotopic map in the lateral motor cortex of humans, to determine whether it followed the traditional somatotopic order or whether it contained any violations of that somatotopic order. The arm and hand representation had a complex organization in which the arm was relatively emphasized in two areas: one dorsal and the other ventral to a region that emphasized the fingers. This violation of a traditional somatotopic order suggests that the motor cortex is not merely a map of the body but is topographically shaped by other influences, perhaps including correlations in the use of body parts in the motor repertoire.

Representation of Eye Movements and Stimulus Motion in Topographically Organized Areas of Human Posterior Parietal Cortex

The Journal of Neuroscience : the Official Journal of the Society for Neuroscience. Aug, 2008  |  Pubmed ID: 18701699

Recent imaging studies have shown that the human posterior parietal cortex (PPC) contains four topographically organized areas along the intraparietal sulcus (IPS1-IPS4). Using a memory-guided saccade paradigm, we confirmed the locations and retinotopic organization of IPS1-IPS4 and identified two additional areas, IPS5 and superior parietal lobule 1 (SPL1). IPS5 is located at the intersection of the intraparietal and postcentral sulcus; SPL1 branches off the IPS and extends into the superior parietal lobule. Both areas, as well as IPS1-IPS4, each contain a representation of the contralateral visual hemifield. We then probed core functions of the dorsal pathway in these areas, that is, the representation of eye movements and visual motion, to compare the functional characteristics of human PPC to physiologically and anatomically defined areas in monkey PPC. First, as in monkey PPC, a gradient representation of eye movements was found along the IPS with decreasing responses for saccades and increasing responses for smooth pursuit eye movements from posterior/medial to anterior/lateral. The greatest preference for saccades was found in SPL1 and for smooth pursuit in IPS5. Second, and again similar to monkey PPC, all topographically organized PPC areas responded to different types of motion including planar, circular, and radial optic flow, as assessed using adaptation paradigms. Areas in posterior IPS preferred radial optic flow over planar motion, whereas areas in anterior PPC did not show preference for a particular motion type. Together, our results indicate strikingly similar characteristics in the general functional organization of human and monkey PPC, but also reveal some notable differences.

Two Hierarchically Organized Neural Systems for Object Information in Human Visual Cortex

Nature Neuroscience. Feb, 2008  |  Pubmed ID: 18193041

The primate visual system is broadly organized into two segregated processing pathways, a ventral stream for object vision and a dorsal stream for space vision. Here, evidence from functional brain imaging in humans demonstrates that object representations are not confined to the ventral pathway, but can also be found in several areas along the dorsal pathway. In both streams, areas at intermediate processing stages in extrastriate cortex (V4, V3A, MT and V7) showed object-selective but viewpoint- and size-specific responses. In contrast, higher-order areas in lateral occipital and posterior parietal cortex (LOC, IPS1 and IPS2) responded selectively to objects independent of image transformations. Contrary to the two-pathways hypothesis, our findings indicate that basic object information related to shape, size and viewpoint may be represented similarly in two parallel and hierarchically organized neural systems in the ventral and dorsal visual pathways.

Effects of Sustained Spatial Attention in the Human Lateral Geniculate Nucleus and Superior Colliculus

The Journal of Neuroscience : the Official Journal of the Society for Neuroscience. Feb, 2009  |  Pubmed ID: 19211885

The role of subcortical visual structures such as the lateral geniculate nucleus (LGN) and the superior colliculus (SC) in the control of visual spatial attention remains poorly understood. Here, we used high-resolution functional magnetic resonance imaging to measure responses in the human LGN and SC during sustained spatial attention. Subjects covertly and continuously tracked one of two segments that rotated through the visual field, composed of either moving dots or transient colored shapes. Activity in both nuclei was generally enhanced by attention, independent of the stimulus type, with the voxels responding more sensitively to stimulus contrast (those dominated by magnocellular input) exhibiting greater attentional enhancement. The LGN contained clusters of voxels exhibiting attentional enhancement or weak suppression, whereas the SC exhibited predominantly attentional enhancement, which was significantly stronger than in the LGN. The spatial distribution of the attentional effects was unrelated to the retinotopic organization in either structure. The results demonstrate that each of the major subcortical visual pathways participates in attentional selection, and their differential magnitudes of modulation suggest distinct roles.

Neural Representations of Faces and Body Parts in Macaque and Human Cortex: a Comparative FMRI Study

Journal of Neurophysiology. May, 2009  |  Pubmed ID: 19225169

Single-cell studies in the macaque have reported selective neural responses evoked by visual presentations of faces and bodies. Consistent with these findings, functional magnetic resonance imaging studies in humans and monkeys indicate that regions in temporal cortex respond preferentially to faces and bodies. However, it is not clear how these areas correspond across the two species. Here, we directly compared category-selective areas in macaques and humans using virtually identical techniques. In the macaque, several face- and body part-selective areas were found located along the superior temporal sulcus (STS) and middle temporal gyrus (MTG). In the human, similar to previous studies, face-selective areas were found in ventral occipital and temporal cortex and an additional face-selective area was found in the anterior temporal cortex. Face-selective areas were also found in lateral temporal cortex, including the previously reported posterior STS area. Body part-selective areas were identified in the human fusiform gyrus and lateral occipitotemporal cortex. In a first experiment, both monkey and human subjects were presented with pictures of faces, body parts, foods, scenes, and man-made objects, to examine the response profiles of each category-selective area to the five stimulus types. In a second experiment, face processing was examined by presenting upright and inverted faces. By comparing the responses and spatial relationships of the areas, we propose potential correspondences across species. Adjacent and overlapping areas in the macaque anterior STS/MTG responded strongly to both faces and body parts, similar to areas in the human fusiform gyrus and posterior STS. Furthermore, face-selective areas on the ventral bank of the STS/MTG discriminated both upright and inverted faces from objects, similar to areas in the human ventral temporal cortex. Overall, our findings demonstrate commonalities and differences in the wide-scale brain organization between the two species and provide an initial step toward establishing functionally homologous category-selective areas.

Carrot Sticks or Joysticks: Video Games Improve Vision

Nature Neuroscience. May, 2009  |  Pubmed ID: 19396229

Attentional Demands Predict Short-term Memory Load Response in Posterior Parietal Cortex

Neuropsychologia. Jul, 2009  |  Pubmed ID: 19428411

Limits to the capacity of visual short-term memory (VSTM) indicate a maximum storage of only 3 or 4 items. Recently, it has been suggested that activity in a specific part of the brain, the posterior parietal cortex (PPC), is correlated with behavioral estimates of VSTM capacity and might reflect a capacity-limited store. In three experiments that varied the delay period and the stimuli to be stored, we found dissociations between functional magnetic resonance imaging (fMRI) activity in PPC and behavioral measures of capacity. When the delay length increased, fMRI activity in this area increased with memory load beyond the behaviorally determined limits of capacity. The results suggest that activity in PPC may reflect the attentional demands of short-term memory rehearsal processes rather than capacity limitations, and imply that a larger number of items than that determined by behavioral measures of capacity may be rehearsed during STM tasks. This account is consistent with the role of PPC in attentional processes and with the close correlation between brain areas that are involved in attention and those that mediate STM.

Neural Mechanisms of Rapid Natural Scene Categorization in Human Visual Cortex

Nature. Jul, 2009  |  Pubmed ID: 19506558

The visual system has an extraordinary capability to extract categorical information from complex natural scenes. For example, subjects are able to rapidly detect the presence of object categories such as animals or vehicles in new scenes that are presented very briefly. This is even true when subjects do not pay attention to the scenes and simultaneously perform an unrelated attentionally demanding task, a stark contrast to the capacity limitations predicted by most theories of visual attention. Here we show a neural basis for rapid natural scene categorization in the visual cortex, using functional magnetic resonance imaging and an object categorization task in which subjects detected the presence of people or cars in briefly presented natural scenes. The multi-voxel pattern of neural activity in the object-selective cortex evoked by the natural scenes contained information about the presence of the target category, even when the scenes were task-irrelevant and presented outside the focus of spatial attention. These findings indicate that the rapid detection of categorical information in natural scenes is mediated by a category-specific biasing mechanism in object-selective cortex that operates in parallel across the visual field, and biases information processing in favour of objects belonging to the target object category.

Gain Control in the Visual Thalamus During Perception and Cognition

Current Opinion in Neurobiology. Aug, 2009  |  Pubmed ID: 19556121

The thalamus has traditionally been thought to passively relay sensory information to the cortex. By showing that responses in visual thalamus are modulated by perceptual and cognitive tasks, recent fMRI and physiology studies have helped revise this view. The modulatory input to the visual thalamus derives from functionally distinct cortical and subcortical feedback pathways. These pathways enable the lateral geniculate nucleus and pulvinar to regulate the information transmitted to cortical areas according to cognitive requirements. Emerging evidence suggests that such regulation involves changing the degree of synchrony between neurons as well as changing the magnitude of thalamic activity. These findings support a role for the thalamus that extends as far as contributing to the control of visual attention and awareness.

Overt and Covert Visual Search in Primates: Reaction Times and Gaze Shift Strategies

Journal of Integrative Neuroscience. Jun, 2009  |  Pubmed ID: 19618485

In order to investigate the search performance and strategies of nonhuman primates, two macaque monkeys were trained to search for a target template among differently oriented distractors in both free-gaze and fixed-gaze viewing conditions (overt and covert search). In free-gaze search, reaction times (RT) and eye movements revealed the theoretically predicted characteristics of exhaustive and self-terminating serial search, with certain exceptions that are also observed in humans. RT was linearly related to the number of fixations but not necessarily to the number of items on display. Animals scanned the scenes in a nonrandom manner spending notably more time on targets and items inspected last (just before reaction). The characteristics of free-gaze search were then compared with search performance under fixed gaze (covert search) and with the performance of four human subjects tested in similar experiments. By and large the performance characteristics of both groups were similar; monkeys were slightly faster, and humans more accurate. Both species produced shorter RT in fixed-gaze than in free-gaze search. But while RT slopes of the human subjects still showed the theoretically predicted difference between hits and rejections, slopes of the two monkeys appeared to collapse. Despite considerable priming and short-term learning when similar tests were continuously repeated, no substantial long-term training effects were seen when test conditions and set sizes were frequently varied. Altogether, the data reveal many similarities between human and monkey search behavior but indicate that search is not necessarily restricted to exclusively serial processes.

A Nonvisual Look at the Functional Organization of Visual Cortex

Neuron. Aug, 2009  |  Pubmed ID: 19679069

In this issue of Neuron, Mahon et al. show that the ventral visual cortex of congenitally blind individuals, who have never experienced the visual world, has an object-category organization similar to that found in sighted individuals. Here, we discuss the implications of this finding for our understanding of the "visual" cortex.

Retinotopic Organization of Human Ventral Visual Cortex

The Journal of Neuroscience : the Official Journal of the Society for Neuroscience. Aug, 2009  |  Pubmed ID: 19710316

Functional magnetic resonance imaging studies have shown that human ventral visual cortex anterior to human visual area V4 contains two visual field maps, VO-1 and VO-2, that together form the ventral occipital (VO) cluster (Brewer et al., 2005). This cluster is characterized by common functional response properties and responds preferentially to color and object stimuli. Here, we confirm the topographic and functional characteristics of the VO cluster and describe two new visual field maps that are located anterior to VO-2 extending across the collateral sulcus into the posterior parahippocampal cortex (PHC). We refer to these visual field maps as parahippocampal areas PHC-1 and PHC-2. Each PHC map contains a topographic representation of contralateral visual space. The polar angle representation in PHC-1 extends from regions near the lower vertical meridian (that is the shared border with VO-2) to those close to the upper vertical meridian (that is the shared border with PHC-2). The polar angle representation in PHC-2 is a mirror reversal of the PHC-1 representation. PHC-1 and PHC-2 share a foveal representation and show a strong bias toward representations of peripheral eccentricities. Both the foveal and peripheral representations of PHC-1 and PHC-2 respond more strongly to scenes than to objects or faces, with greater scene preference in PHC-2 than PHC-1. Importantly, both areas heavily overlap with the functionally defined parahippocampal place area. Our results suggest that ventral visual cortex can be subdivided on the basis of topographic criteria into a greater number of discrete maps than previously thought.

Topographic Maps in Human Frontal and Parietal Cortex

Trends in Cognitive Sciences. Nov, 2009  |  Pubmed ID: 19758835

Retinotopic mapping of functional magnetic resonance (fMRI) responses evoked by visual stimuli has resulted in the identification of many areas in human visual cortex and a description of the organization of the visual field representation in each of these areas. These methods have recently been employed in conjunction with tasks that involve higher-order cognitive processes such as spatial attention, working memory, and planning and execution of saccadic eye movements. This approach has led to the discovery of multiple areas in human parietal and frontal areas, each containing a topographic map of visual space. In this review, we summarize the anatomical locations, visual field organization, and functional specialization of these new parietal and frontal topographic cortical areas. The study of higher-order topographic cortex promises to yield unprecedented insights into the neural mechanisms of cognitive processes and, in conjunction with parallel studies in non-human primates, into the evolution of cognition.

Transcranial Magnetic Stimulation Studies of Visuospatial Attentional Control

F1000 Biology Reports. Oct, 2009  |  Pubmed ID: 20161371

Transcranial magnetic stimulation (TMS) is an established technique in cognitive neuroscience which is used to interrupt processing in the brain, creating a brief 'virtual lesion'. Here, we review recent studies that have employed TMS to gain insight into the roles of frontal and parietal cortex in visuospatial attention control.

Top-down and Bottom-up Mechanisms in Biasing Competition in the Human Brain

Vision Research. Jun, 2009  |  Pubmed ID: 18694779

The biased competition theory of selective attention has been an influential neural theory of attention, motivating numerous animal and human studies of visual attention and visual representation. There is now neural evidence in favor of all three of its most basic principles: that representation in the visual system is competitive; that both top-down and bottom-up biasing mechanisms influence the ongoing competition; and that competition is integrated across brain systems. We review the evidence in favor of these three principles, and in particular, findings related to six more specific neural predictions derived from these original principles.

Cardiopulmonary Effects of Dorsal Recumbency and High-volume Caudal Epidural Anaesthesia with Lidocaine or Xylazine in Calves

Veterinary Journal (London, England : 1997). Dec, 2010  |  Pubmed ID: 19766514

The objective of this study was to investigate the cardiopulmonary effects of dorsal recumbency and high-volume caudal epidural anaesthesia induced by xylazine or lidocaine in calves. Twenty-eight German Holstein-Friesian calves (57.7 ± 5.8 kg bodyweight) were randomly allocated to four equal (n=7) groups for one of the following treatments, each injected into the caudal epidural space: (1) no treatment (control); (2) sterile saline (0.4 mL/kg); (3) lidocaine (2%), or (4) xylazine (0.1mg/kg), with the latter two treatments diluted with sterile saline to a final volume of 0.4 mL/kg. Cardiac output was measured by thermodilution and cardiopulmonary function parameters were determined at preset time intervals over an observation period of 335 min. After baseline measurements in the standing animals, the calves received the epidural injection and were positioned in dorsal recumbency for 95 min. In the control group, dorsal recumbency caused a significant (P < 0.05) decrease in cardiac index (CI) (baseline 210 ± 12 mL/kg/min, minimum value 174 ± 11 mL/kg/min), without significant change in blood-gas values. Calves treated with lidocaine or saline did not differ from the control group in any of the parameters measured. The epidural injection of xylazine caused a more pronounced decrease in CI (baseline 209 ± 12 mL/kg/min, minimum value 127 ± 11 mL/kg/min), compared to the control group. At the same time, the heart rate was significantly (P < 0.05) decreased (baseline 113 ± 7 beats per min, minimum value 86 ± 4 beats per min). Furthermore, a significant (P < 0.05) increase in the oxygen extraction ratio was observed in the xylazine group (baseline 39 ± 7%, maximum value 47 ± 7%). In all groups, cardiorespiratory parameters remained within physiological limits. Changes in cardiopulmonary function induced by dorsal recumbency and high-volume caudal epidural anaesthesia with lidocaine or xylazine were well tolerated in healthy calves.

Defining the Units of Competition: Influences of Perceptual Organization on Competitive Interactions in Human Visual Cortex

Journal of Cognitive Neuroscience. Nov, 2010  |  Pubmed ID: 19925189

Multiple stimuli that are present simultaneously in the visual field compete for neural representation. At the same time, however, multiple stimuli in cluttered scenes also undergo perceptual organization according to certain rules originally defined by the Gestalt psychologists such as similarity or proximity, thereby segmenting scenes into candidate objects. How can these two seemingly orthogonal neural processes that occur early in the visual processing stream be reconciled? One possibility is that competition occurs among perceptual groups rather than at the level of elements within a group. We probed this idea using fMRI by assessing competitive interactions across visual cortex in displays containing varying degrees of perceptual organization or perceptual grouping (Grp). In strong Grp displays, elements were arranged such that either an illusory figure or a group of collinear elements were present, whereas in weak Grp displays the same elements were arranged randomly. Competitive interactions among stimuli were overcome throughout early visual cortex and V4, when elements were grouped regardless of Grp type. Our findings suggest that context-dependent grouping mechanisms and competitive interactions are linked to provide a bottom-up bias toward candidate objects in cluttered scenes.

Mechanisms of Spatial Attention Control in Frontal and Parietal Cortex

The Journal of Neuroscience : the Official Journal of the Society for Neuroscience. Jan, 2010  |  Pubmed ID: 20053897

Theories of spatial attentional control have been largely based upon studies of patients suffering from visuospatial neglect, resulting from circumscribed lesions of frontal and posterior parietal cortex. In the intact brain, the control of spatial attention has been related to a distributed frontoparietal attention network. Little is known about the nature of the control mechanisms exerted by this network. Here, we used a novel region-of-interest approach to relate activations of the attention network to recently described topographic areas in frontal cortex [frontal eye field (FEF), PreCC/IFS (precentral cortex/inferior frontal sulcus)] and parietal cortex [intraparietal sulcus areas (IPS1-IPS5) and an area in the superior parietal lobule (SPL1)] to examine their spatial attention signals. We found that attention signals in most topographic areas were spatially specific, with stronger responses when attention was directed to the contralateral than to the ipsilateral visual field. Importantly, two hemispheric asymmetries were found. First, a region in only right, but not left SPL1 carried spatial attention signals. Second, left FEF and left posterior parietal cortex (IPS1/2) generated stronger contralateral biasing signals than their counterparts in the right hemisphere. These findings are the first to characterize spatial attention signals in topographic frontal and parietal cortex and provide a neural basis in support of an interhemispheric competition account of spatial attentional control.

Electroencephalographic Recordings in Dogs: Prevention of Muscle Artifacts and Evaluation of Two Activation Techniques in Healthy Individuals

Research in Veterinary Science. Apr, 2011  |  Pubmed ID: 20591453

This study was performed to improve a standard anesthetic protocol for electroencephalography (EEG) in dogs and to evaluate the effect of photic stimulation and hyperventilation on the EEG of healthy dogs. Ten clinically and neurologically normal beagle dogs were anesthetized with propofol given intravenously with average doses of 7.5mg/kg for induction and 0.37mg/kg/min constant rate infusion for maintenance. Rocuronium bromide (0.4mg/kg IV) was used as a peripheral muscle relaxant in order to prevent muscle artifacts. EEGs were recorded digitally using five subdermal needle electrodes. Photic stimulation and hyperventilation were performed to evaluate two activation techniques commonly used in human EEG recording methods. Monopolar and bipolar montages were analyzed visually and quantitatively. The use of rocuronium produced muscle artifact-free EEG recordings during the given recording procedure which indicates that rocuronium is a valuable adjunct to anesthesia during EEG recording. Photic stimulation and hyperventilation did not provoke paroxysmal discharges in the EEG of healthy dogs. Analysis of quantitative EEG data showed that background activity did not differ significantly between periods with and without stimulation. This data are important basic values and will further help to compare the effects of photic stimulation and hyperventilation of healthy dogs and those suffering from epilepsy.

Functional Heterogeneity of Conflict, Error, Task-switching, and Unexpectedness Effects Within Medial Prefrontal Cortex

NeuroImage. Jan, 2011  |  Pubmed ID: 20728547

The last decade has seen considerable discussion regarding a theoretical account of medial prefrontal cortex (mPFC) function with particular focus on the anterior cingulate cortex. The proposed theories have included conflict detection, error likelihood prediction, volatility monitoring, and several distinct theories of error detection. Arguments for and against particular theories often treat mPFC as functionally homogeneous, or at least nearly so, despite some evidence for distinct functional subregions. Here we used functional magnetic resonance imaging (fMRI) to simultaneously contrast multiple effects of error, conflict, and task-switching that have been individually construed in support of various theories. We found overlapping yet functionally distinct subregions of mPFC, with activations related to dominant error, conflict, and task-switching effects successively found along a rostral-ventral to caudal-dorsal gradient within medial prefrontal cortex. Activations in the rostral cingulate zone (RCZ) were strongly correlated with the unexpectedness of outcomes suggesting a role in outcome prediction and preparing control systems to deal with anticipated outcomes. The results as a whole support a resolution of some ongoing debates in that distinct theories may each pertain to corresponding distinct yet overlapping subregions of mPFC.

Interactions of Top-down and Bottom-up Mechanisms in Human Visual Cortex

The Journal of Neuroscience : the Official Journal of the Society for Neuroscience. Jan, 2011  |  Pubmed ID: 21228167

Multiple stimuli present in the visual field at the same time compete for neural representation by mutually suppressing their evoked activity throughout visual cortex, providing a neural correlate for the limited processing capacity of the visual system. Competitive interactions among stimuli can be counteracted by top-down, goal-directed mechanisms such as attention, and by bottom-up, stimulus-driven mechanisms. Because these two processes cooperate in everyday life to bias processing toward behaviorally relevant or particularly salient stimuli, it has proven difficult to study interactions between top-down and bottom-up mechanisms. Here, we used an experimental paradigm in which we first isolated the effects of a bottom-up influence on neural competition by parametrically varying the degree of perceptual grouping in displays that were not attended. Second, we probed the effects of directed attention on the competitive interactions induced with the parametric design. We found that the amount of attentional modulation varied linearly with the degree of competition left unresolved by bottom-up processes, such that attentional modulation was greatest when neural competition was little influenced by bottom-up mechanisms and smallest when competition was strongly influenced by bottom-up mechanisms. These findings suggest that the strength of attentional modulation in the visual system is constrained by the degree to which competitive interactions have been resolved by bottom-up processes related to the segmentation of scenes into candidate objects.

Visuotopic Organization of Macaque Posterior Parietal Cortex: a Functional Magnetic Resonance Imaging Study

The Journal of Neuroscience : the Official Journal of the Society for Neuroscience. Feb, 2011  |  Pubmed ID: 21307244

Macaque anatomy and physiology studies have revealed multiple visual areas in posterior parietal cortex (PPC). While many response properties of PPC neurons have been probed, little is known about PPC's large-scale functional topography-specifically related to visuotopic organization. Using high-resolution functional magnetic resonance imaging at 3 T with a phase-encoded retinotopic mapping paradigm in the awake macaque, a large-scale visuotopic organization along lateral portions of PPC anterior to area V3a and extending into the lateral intraparietal sulcus (LIP) was found. We identify two new visual field maps anterior to V3a within caudal PPC, referred to as caudal intraparietal-1 (CIP-1) and CIP-2. The polar angle representation in CIP-1 extends from regions near the upper vertical meridian (that is the shared border with V3a and dorsal prelunate) to those within the lower visual field (that is the shared border with CIP-2). The polar angle representation in CIP-2 is a mirror reversal of the CIP-1 representation. CIP-1 and CIP-2 share a representation of central space on the lateral border. Anterior to CIP-2, a third polar angle representation was found within LIP, referred to as visuotopic LIP. The polar angle representation in LIP extends from regions near the upper vertical meridian (that is the shared border with CIP-2) to those near the lower vertical meridian. Representations of central visual space were identified within dorsal portions of LIP with peripheral representations in ventral portions. We also consider the topographic large-scale organization found within macaque PPC relative to that observed in human PPC.

Intermittent Positive Pressure Ventilation with Constant Positive End-expiratory Pressure and Alveolar Recruitment Manoeuvre During Inhalation Anaesthesia in Horses Undergoing Surgery for Colic, and Its Influence on the Early Recovery Period

Veterinary Anaesthesia and Analgesia. May, 2011  |  Pubmed ID: 21492381

To compare, ventilation using intermittent positive pressure ventilation (IPPV) with constant positive end-expiratory pressure (PEEP) and alveolar recruitment manoeuvres (RM) to classical IPPV without PEEP on gas exchange during anaesthesia and early recovery.

A Neural Basis for Real-world Visual Search in Human Occipitotemporal Cortex

Proceedings of the National Academy of Sciences of the United States of America. Jul, 2011  |  Pubmed ID: 21730192

Mammals are highly skilled in rapidly detecting objects in cluttered natural environments, a skill necessary for survival. What are the neural mechanisms mediating detection of objects in natural scenes? Here, we use human brain imaging to address the role of top-down preparatory processes in the detection of familiar object categories in real-world environments. Brain activity was measured while participants were preparing to detect highly variable depictions of people or cars in natural scenes that were new to the participants. The preparation to detect objects of the target category, in the absence of visual input, evoked activity patterns in visual cortex that resembled the response to actual exemplars of the target category. Importantly, the selectivity of multivoxel preparatory activity patterns in object-selective cortex (OSC) predicted target detection performance. By contrast, preparatory activity in early visual cortex (V1) was negatively related to search performance. Additional behavioral results suggested that the dissociation between OSC and V1 reflected the use of different search strategies, linking OSC preparatory activity to relatively abstract search preparation and V1 to more specific imagery-like preparation. Finally, whole-brain searchlight analyses revealed that, in addition to OSC, response patterns in medial prefrontal cortex distinguished the target categories based on the search cues alone, suggesting that this region may constitute a top-down source of preparatory activity observed in visual cortex. These results indicate that in naturalistic situations, when the precise visual characteristics of target objects are not known in advance, preparatory activity at higher levels of the visual hierarchy selectively mediates visual search.

Effects of Sleep Deprivation on Cortical Activation During Directed Attention in the Absence and Presence of Visual Stimuli

NeuroImage. Sep, 2011  |  Pubmed ID: 21745579

Sleep deprivation (SD) can give rise to faltering attention but the mechanics underlying this remain uncertain. Using a covert attention task that required attention to a peripheral target location, we compared the effects of attention and SD on baseline activity prior to visual stimulation as well as on stimulus-evoked activity. Volunteers were studied after a night of normal sleep (RW) and a night of SD. Baseline signal elevations evoked by preparatory attention in the absence of visual stimulation were attenuated within rFEF, rIPS (sparing SEF) and all retinotopically mapped visual areas during SD, indicative of impaired endogenous attention. In response to visual stimuli, attention modulated activation in higher cortical areas and extrastriate cortex (hV4, ventral occipital areas) after RW. SD attenuated rFEF, rIPS, V3a and VO stimulus-evoked activation regardless of whether stimuli were attended. Notably, the modulation of stimulus-evoked activation by attention was not affected by SD unlike for the preparatory period, suggesting a reduced number, but still functional circuits during SD. Deficits in endogenous attention in SD dominate in the preparatory period, whereas changes in stimulus-related activation arise from an interaction between compromised fronto-parietal top-down control of attention and reduced sensitivity of extrastriate visual cortex to top-down or bottom-up inputs.

The Functional Neuroanatomy of Object Agnosia: a Case Study

Neuron. Jul, 2011  |  Pubmed ID: 21745637

Cortical reorganization of visual and object representations following neural injury was examined using fMRI and behavioral investigations. We probed the visual responsivity of the ventral visual cortex of an agnosic patient who was impaired at object recognition following a lesion to the right lateral fusiform gyrus. In both hemispheres, retinotopic mapping revealed typical topographic organization and visual activation of early visual cortex. However, visual responses, object-related, and -selective responses were reduced in regions immediately surrounding the lesion in the right hemisphere, and also, surprisingly, in corresponding locations in the structurally intact left hemisphere. In contrast, hV4 of the right hemisphere showed expanded response properties. These findings indicate that the right lateral fusiform gyrus is critically involved in object recognition and that an impairment to this region has widespread consequences for remote parts of cortex. Finally, functional neural plasticity is possible even when a cortical lesion is sustained in adulthood.

Cognitive and Perceptual Functions of the Visual Thalamus

Neuron. Jul, 2011  |  Pubmed ID: 21791281

The thalamus is classically viewed as passively relaying information to the cortex. However, there is growing evidence that the thalamus actively regulates information transmission to the cortex and between cortical areas using a variety of mechanisms, including the modulation of response magnitude, firing mode, and synchrony of neurons according to behavioral demands. We discuss how the visual thalamus contributes to attention, awareness, and visually guided actions, to present a general role for the thalamus in perception and cognition.

Is That a Bathtub in Your Kitchen?

Nature Neuroscience. Oct, 2011  |  Pubmed ID: 21952264

Electroencephalographic Recordings in Dogs Suffering from Idiopathic and Symptomatic Epilepsy: Diagnostic Value of Interictal Short Time EEG Protocols Supplemented by Two Activation Techniques

Veterinary Journal (London, England : 1997). Nov, 2011  |  Pubmed ID: 22099183

The diagnostic value of interictal short time electroencephalographic (EEG) recordings in epileptic dogs under general anaesthesia with propofol and the muscle relaxant rocuronium bromide was investigated. Two activation techniques, namely photic stimulation and hyperventilation, were evaluated for their potential to enhance the diagnostic validity of these recordings. Sixty-one dogs suffering from idiopathic epilepsy and 28 dogs suffering from symptomatic epilepsy were included. Electroencephalograms were recorded using five subdermal EEG electrodes (F3, F4, Cz, O1 and O2). All 89 EEGs were analysed visually and 61 were also evaluated quantitatively with fast Fourier transformation. Interictal paroxysmal epileptiform activity was found in 25% of idiopathic and in 29% of symptomatic epileptic dogs. Quantitative analysis of the EEGs (qEEGs) detected significant differences of frequency analysis in single reading points without any continuous changes of frequency bands. A comparison between healthy and affected brain hemispheres in seven dogs with focal lesions of one hemisphere did not show any significant differences in qEEG analysis. qEEG was not more sensitive than visual evaluation. Despite the use of activation techniques, the results showed that short time EEG recordings in epileptic dogs can detect interictal epileptic activity in less than one third of all seizuring dogs and is not a useful screening method.

Human Consciousness and Its Relationship to Social Neuroscience: A Novel Hypothesis

Cognitive Neuroscience. Jan, 2011  |  Pubmed ID: 22121395

A common modern view of consciousness is that it is an emergent property of the brain, perhaps caused by neuronal complexity, and perhaps with no adaptive value. Exactly what emerges, how it emerges, and from what specific neuronal process, is in debate. One possible explanation of consciousness, proposed here, is that it is a construct of the social perceptual machinery. Humans have specialized neuronal machinery that allows us to be socially intelligent. The primary role for this machinery is to construct models of other people's minds thereby gaining some ability to predict the behavior of other individuals. In the present hypothesis, awareness is a perceptual reconstruction of attentional state; and the machinery that computes information about other people's awareness is the same machinery that computes information about our own awareness. The present article brings together a variety of lines of evidence including experiments on the neural basis of social perception, on hemispatial neglect, on the out-of-body experience, on mirror neurons, and on the mechanisms of decision-making, to explore the possibility that awareness is a construct of the social machinery in the brain.