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Articles by Kazuo Okanoya in JoVE
JoVE General
Применение Светоотверждаемый Стоматологическая смолы Клей для монтажа электродов или Микродиализ зонды в хронических опытах
1Laboratory for Behavior and Dynamic Cognition, Brain Science Institute, RIKEN, 2Laboratory for Biolinguistics, Brain Science Institute, RIKEN
В этом докладе, мы предлагаем новое применение светоотверждаемых стоматологических смол для монтажа базе электродных или микродиализа зонды в хронических опытах. Этот материал позволяет осуществлять прямую связь с черепом.
Other articles by Kazuo Okanoya on PubMed
Localization of the Cytochrome P450 Side-chain Cleavage Enzyme in the Inactive Testis of the Naked Mole-rat
Spermatogenesis was histologically examined in non-breeding male of the naked mole rat (Heterocephalus glaber) using a light microscopy. Spermatogonia, spermatocytes and spermatids were confirmed in the seminiferous tubules. However, the spermatogenesis was disordered, and many spermatocytes and spermatids were sloughing. Sperms could not be seen in the lumen of the tubules. The characteristic accumulation of interstitial cells was the most noteworthy. In the immunohistochemistry for cytochrome p450 side-chain cleavage enzyme, immunoreactions were not entirely distributed in each interstitial cell, although positive reactions were scattered in the interstitial cell-mass. The findings indicate that few interstitial cells act as a testosterone-synthesizing apparatus in the characteristic structure with accumulated cell-mass. From the immunohistochemical data we suggest the possibility that spermatogonia and Sertoli cells may secrete 17 beta-estradiol. We also suggest that 17 beta-estradiol from spermatogonia and Sertoli cells may inhibit the interstitial cells from synthesizing and secreting testosterone and may suppress the later stages of the spermatogenesis to induce apoptosis of germ cells. The TUNEL methods demonstrated that cell death occurred in some spermatocytes in non-breeding males.
Context-dependent Song Amplitude Control in Bengalese Finches
Estrildid finches have two song types: directed (courtship) and undirected (solo). These are acoustically identical and differ only in social context. Recent studies have shown that undirected singing is accompanied by strong activation of the basal ganglia pathway, whereas directed singing is not, which suggests a different degree of feedback control between the two. We examined whether the magnitude of the Lombard effect, i.e., vocal amplitude regulation in response to environmental noise, differed based on the song context. Our results indicate that Bengalese finches change the amplitude of undirected song based on background noise levels, but do not do so for directed song. This is the first behavioral evidence suggesting that feedback control of song output vary by social context.
Spontaneous Vocal Differentiation of Coo-calls for Tools and Food in Japanese Monkeys
Vocal production and its usage in nonhuman primates may share common features with primitive human language. We trained two Japanese monkeys to use a rake-shaped tool to retrieve distant food. After the training, the monkeys spontaneously began vocalizing coo-calls in the tool-using context. We then trained one of the monkeys to vocalize to request food or the tool. Three independent acoustic parameters were measured and each parameter was independently analyzed across conditions using a multiple comparison test. We found that the monkey spontaneously differentiated their coo-calls to ask for either food or tool during the course of this training. This process might involve a change from emotional vocalizations into intentionally controlled ones by associating them with consciously planned tool use. We thus established a novel hypothesis about the origin of voluntary vocal control that could be approached from neurophysiological procedures.
Song Syntax Changes in Bengalese Finches Singing in a Helium Atmosphere
Male Bengalese finches rely heavily on hearing to maintain adult songs and deafening a bird changes its song syntax immediately. Eight adult male Bengalese finches were placed in a helium atmosphere, which changes the resonance of the vocal tract. Undirected songs were recorded before, during and after this procedure, and the changes in song structure were analyzed. A helium environment increases the amplitude of higher harmonics, as in other bird species. Furthermore, note-to-note transition patterns that were never recorded when singing in normal air appeared in the songs sung in helium air. Therefore, helium can be used to cause reversible syntactical re-organization of songs in Bengalese finches, which can be used to study the neural mechanisms of auditory feedback.
Neural Correlates of Song Complexity in Bengalese Finch High Vocal Center
Auditory neurons in the songbird forebrain nucleus high vocal center HVC) show high selectivity to the temporal structure of bird's own song but the relationship between the degree of song complexity and neural selectivity is not known. We investigated the song temporal selectivity of HVC neurons by multi-unit recordings in seven male Bengalese finches with different song complexity. Results showed that HVC multi-units of the individuals with more complex songs responded strongly to each of the self-generated song elements but were relatively insensitive to the element order, while those with stereotyped songs responded only to the song elements ordered exactly as in the self-produced songs. Data suggest that the individually learned song syntax correlates with individualized temporal combination selectivity in HVC neurons.
The Bengalese Finch: a Window on the Behavioral Neurobiology of Birdsong Syntax
The Bengalese finch Lonchura striata var. domestica is a domesticated strain of a wild species, the white-rumped munia Lonchura striata of Southeast Asia. Bengalese finches have been domesticated in Japan for 240 years. Comparing their song syntax with that of their wild ancestors, we found that the domesticated strain has highly complex, conspicuous songs with finite-state syntax, while the wild ancestor sang very stereotyped linear songs. To examine the functional utility of the song complexity, we compared serum levels of estradiol and measured the amount of nesting materials carried into the nest by female birds that were stimulated with either the complex "domesticated" song or the simple wild-type song. In the females stimulated with complex songs the estradiol levels were significantly higher and the amount of nesting material carried was significantly greater. We then performed brain lesions in the song system to identify the neural substrates that are responsible for these differences in song behavior. In Bengalese finches lesions of NIf, a higher order song control nucleus, resulted in simplification of the complex song syntax. That is, the complex "domesticated" syntax changed into the simple wild-type syntax. Based on these data, we hypothesize that mutations in the song control nuclei have occurred that enabled complex song syntax and became fixed into the population of domesticated Bengalese finches through a process of indirect sexual selection.
Spatiotemporal Properties of Visual Stimuli for Song Induction in Bengalese Finches
Male Bengalese finches sing directed songs in response to video images of females projected onto a thin-film transistor monitor. We used this experimental paradigm to elucidate which properties of visual stimuli are important for eliciting singing. When video recordings of female Bengalese or zebra finches were used as visual stimuli, only images of conspecific females elicited singing from male Bengalese finches. When images of female Bengalese finches were rotated by 0 degrees, 90 degrees, or 180 degrees, only the upright images elicited singing. Finally, temporally normal (forward playback) images were more effective than time-reversed images and still images for eliciting singing. These results suggest that both the spatial and temporal arrangements of visual stimuli affect the singing behavior of male finches.
Sex Differences in the Telencephalic Song Control Circuitry in Bengalese Finches (Lonchura Striata Var. Domestica)
Bengalese finches, Lonchura striata, are extremely sexually dimorphic in their singing behavior; males sing complex songs, whereas females do not sing at all. This study describes the developmental differentiation of the brain song system in Bengalese finches. Nissl staining was used to measure the volumes of four telencephalic song nuclei: Area X, HVC, the robust nucleus of the arcopallium (RA), and the lateral portion of the magnocellular nucleus of the anterior nidopallium (LMAN). In juveniles (circa 35 days old), Area X and the HVC were well developed in males, while they were absent or not discernable in females. The RA was much larger in males but barely discernable in females. In males, the volumes of Area X and the RA increased further into adulthood, but that of the HVC remained unchanged. The LMAN volume was greater in juveniles than in adults, and there was no difference in the LMAN volume between the sexes. The overall tendency was similar to that described in zebra finches, except for the volume of the RA, where the degree of sexual dimorphism is larger and the timing of differentiation occurs earlier in Bengalese finches. Motor learning of the song continues until day 90 in zebra finches, but up to day 120 in Bengalese finches. Earlier neural differentiation and a longer learning period in Bengalese finches compared with zebra finches may be related to the more elaborate song structures of Bengalese finches.
Language Evolution and an Emergent Property
Much debate has been stimulated by the recent hypothesis that human language consists of a faculty that is shared with non-human animals (faculty of language in a broad sense; FLB) and a faculty that is specific to human language (faculty of language in a narrow sense; FLN). This hypothesis has encouraged a tendency to emphasize one component of FLN: the cognitive operation of recursion. In consequence, non-syntactical, yet unique, aspects of human language have been neglected. One of these properties consists of vocal learning that enables an abundance of learned syllables. I suggest that FLN is not an independent faculty, but an 'emergent' property, arising from interactions between several other non-syntactical subfaculties of FLB, including vocal learning ability.
Prefrontal Activity During Koh-do Incense Discrimination
Whenever we make reasoned decisions we must refer to relevant knowledge obtained through past experience. Our brains test multiple premises and select whichever conclusion serves as the best explanation of the current conditions. In the present study we examined the prefrontal activity of koh-do experts with near infrared spectroscopy while they reasoned about odours during an incense discrimination task. These practitioners of the Japanese incense ceremony have been trained to form and manipulate abstract images of complex olfactory stimuli represented in a multidimensional symbolic space in the mind. In koh-do experts, the right PFC showed a consistent stimulus-non-selective response during discrimination and the left PFC showed phasic stimulus-selective responses modulated by the internal subjective state of the reasoning process. These two dissociated functions appeared to cooperate with each other during reasoning. In contrast, koh-do beginners did not show the organized response pattern found in experts. The results suggest that both PFCs contribute to abductive reasoning, but do so differently through different stages of the process.
A Neural Network Model for Generating Complex Birdsong Syntax
The singing behavior of songbirds has been investigated as a model of sequence learning and production. The song of the Bengalese finch, Lonchura striata var. domestica, is well described by a finite state automaton including a stochastic transition of the note sequence, which can be regarded as a higher-order Markov process. Focusing on the neural structure of songbirds, we propose a neural network model that generates higher-order Markov processes. The neurons in the robust nucleus of the archistriatum (RA) encode each note; they are activated by RA-projecting neurons in the HVC (used as a proper name). We hypothesize that the same note included in different chunks is encoded by distinct RA-projecting neuron groups. From this assumption, the output sequence of RA is a higher-order Markov process, even though the RA-projecting neurons in the HVC fire on first-order Markov processes. We developed a neural network model of the local circuits in the HVC that explains the mechanism by which RA-projecting neurons transit stochastically on first-order Markov processes. Numerical simulation showed that this model can generate first-order Markov process song sequences.
On-line Assessment of Statistical Learning by Event-related Potentials
Abstract We investigated the neural processes involved in on-line statistical learning and word segmentation. Auditory event-related potentials (ERPs) were recorded while participants were exposed to continuous, nonlinguistic auditory sequences, the elements of which were organized into "tritone words" that were sequenced in random order, with no silent spaces between them. After listening to three 6.6-min sessions of sequences, the participants performed a behavioral choice test, in which they were instructed to indicate the most familiar tone sequence in each test trial by pressing buttons. The participants were divided into three groups (high, middle, and low learners) based on their behavioral performance. The overall mean performance was 74.4%, indicating that the tone sequence was segmented and that the participants learned the tone words statistically. Grand-averaged ERPs showed that word onset (initial tone) elicited the largest N100 and N400 in the early learning session of high learners, but in middle learners, the word-onset effect was elicited in a later session, and there was no effect in low learners. The N400 amplitudes significantly differed between the three learning sessions in the high- and middle-learner groups. The results suggest that the N400 effect indicates not only on-line word segmentation but also the degree of statistical learning. This study provides insight into the neural mechanisms underlying on-line statistical learning processes.
Sex Differences in Audiovisual Discrimination Learning by Bengalese Finches (Lonchura Striata Var. Domestica)
Both visual and auditory information are important for songbirds, especially in developmental and sexual contexts. To investigate bimodal cognition in songbirds, the authors conducted audiovisual discrimination training in Bengalese finches. The authors used two types of stimulus: an "artificial stimulus," which is a combination of simple figures and sound, and a "biological stimulus," consisting of video images of singing males along with their songs. The authors found that while both sexes predominantly used visual cues in the discrimination tasks, males tended to be more dependent on auditory information for the biological stimulus. Female responses were always dependent on the visual stimulus for both stimulus types. Only males changed their discrimination strategy according to stimulus type. Although males used both visual and auditory cues for the biological stimulus, they responded to the artificial stimulus depending only on visual information, as the females did. These findings suggest a sex difference in innate auditory sensitivity.
Expression Analysis of Cadherins in the Songbird Brain: Relationship to Vocal System Development
Songbirds learn their songs as juveniles. The brains of songbirds have a series of nuclei and neural circuits called the song system, which is indispensable for vocal learning and production. In the present study we analyzed the expression patterns of cell adhesion molecules, cadherins, in the Bengalese finch (Lonchura striata var. domestica) to investigate their potential involvement in song nuclei and neural circuit formation. We found that cadherin-6B was expressed in many song nuclei of the juvenile and adult brain, while R-cadherin was complementarily expressed in surrounding areas. On the other hand, cadherin-7 was expressed in the robust nucleus of the arcopallium (RA) in the sensory learning stage, and its expression was downregulated during the sensorimotor learning stage. This downregulation of cadherin-7 was sexually dimorphic, suggesting its involvement in song development. Other cadherins, including cadherin-9, -10, and -12, showed different song-nuclei-related expression profiles. These patterns of song nuclei related expression suggest the possibility that cadherins are involved in the formation and maintenance of the song nuclei or neural pathways of the song system.
Comparative Analysis of Gene Expressions Among Avian Brains: a Molecular Approach to the Evolution of Vocal Learning
Among avian species, three families of birds (songbirds, parrots, and hummingbirds) learn songs. In the brain of these vocal learners, there are neural networks called 'song systems' that specialize in song learning and production. To explore the evolution of the molecular basis of vocal learning, we conducted a comparative analysis of gene expression in vocal learners (Bengalese finches and budgerigars) and non-learners (quails and pigeons). The expression of one gene is similar in vocal learners, but that of other genes is highly diverse. In non-learners, by contrast, no nuclei-specific expression exists. These results suggest that songbirds and parrots acquired their song systems through both similar and different molecular mechanisms.
Feedback-based Error Monitoring Processes During Musical Performance: an ERP Study
Auditory feedback is important in detecting and correcting errors during sound production when a current performance is compared to an intended performance. In the context of vocal production, a forward model, in which a prediction of action consequence (corollary discharge) is created, has been proposed to explain the dampened activity of the auditory cortex while producing self-generated vocal sounds. However, it is unclear how auditory feedback is processed and what neural mechanism underlies the process during other sound production behavior, such as musical performances. We investigated the neural correlates of human auditory feedback-based error detection using event-related potentials (ERPs) recorded during musical performances. Keyboard players of two different skill levels played simple melodies using a musical score. During the performance, the auditory feedback was occasionally altered. Subjects with early and extensive piano training produced a negative ERP component N210, which was absent in non-trained players. When subjects listened to music that deviated from a corresponding score without playing the piece, N210 did not emerge but the imaginary mismatch negativity (iMMN) did. Therefore, N210 may reflect a process of mismatch between the intended auditory image evoked by motor activity, and actual auditory feedback.
Tool-use Training in a Species of Rodent: the Emergence of an Optimal Motor Strategy and Functional Understanding
Tool use is defined as the manipulation of an inanimate object to change the position or form of a separate object. The expansion of cognitive niches and tool-use capabilities probably stimulated each other in hominid evolution. To understand the causes of cognitive expansion in humans, we need to know the behavioral and neural basis of tool use. Although a wide range of animals exhibit tool use in nature, most studies have focused on primates and birds on behavioral or psychological levels and did not directly address questions of which neural modifications contributed to the emergence of tool use. To investigate such questions, an animal model suitable for cellular and molecular manipulations is needed.
Functional Evidence for Internal Feedback in the Songbird Brain Nucleus HVC
The song control system of songbirds consists mainly of the 'motor pathway' and 'anterior forebrain pathway'. The medial magnocellular nucleus of anterior nidopallium (mMAN) projects to the song control nucleus HVC, which is the point of divergence of the two pathways. We made simultaneous multiunit electrophysiological recordings from the mMAN and HVC in anesthetized Bengalese finches. We confirmed that the mMAN neurons showed song-selective auditory responses, and found temporal correlations between song-related activities of the mMAN and HVC neurons. The temporal relationship between the neural activation of the HVC and mMAN suggests that these nuclei are parts of a closed loop, which could provide internal feedback to the HVC for sequential syllable control.
Vocal Area-related Expression of the Androgen Receptor in the Budgerigar (Melopsittacus Undulatus) Brain
The androgen receptor is a steroid hormone receptor widely expressed in the vocal control nuclei in songbirds. Here, we analysed androgen receptor expression in the brains of juvenile and adult budgerigars. With a species-specific probe for budgerigar androgen receptor mRNA, we found that the androgen receptor was expressed in the vocal areas, such as the central nucleus of the lateral nidopallium, the anterior arcopallium, the oval nucleus of the mesopallium, the oval nucleus of the anterior nidopallium and the tracheosyringeal hypoglossal nucleus. With the present data, together with previous reports, it turned out that the androgen receptor expression in telencephalic vocal control areas is similar amongst three groups of vocal learners--songbirds, hummingbirds and parrots, suggesting the possibility that the androgen receptor might play a role in vocal development and that the molecular mechanism regulating the androgen receptor expression in the vocal areas might be important in the evolution of vocal learning.
Developmental Learning of Complex Syntactical Song in the Bengalese Finch: a Neural Network Model
We developed a neural network model for studying neural mechanisms underlying complex syntactical songs of the Bengalese finch, which result from interactions between sensori-motor nuclei, the nucleus HVC (HVC) and the nucleus interfacialis (NIf). Results of simulations are tested by comparison with the song development of real young birds learning the same songs from their fathers. The model shows that complex syntactical songs can be reproduced from the simple interaction between the deterministic dynamics of a recurrent neural network and random noise. Features of the learning process in the simulations show similar trends to those observed in empirical data on the song development of real birds. These observations suggest that the temporal note sequences of songs take the form of a dynamical process involving recurrent connections in the network of the HVC, as opposed to feedforward activities, the mechanism proposed in the previous model.
Statistical Segmentation of Tone Sequences Activates the Left Inferior Frontal Cortex: a Near-infrared Spectroscopy Study
Word segmentation, that is, discovering the boundaries between words that are embedded in a continuous speech stream, is an important faculty for language learners; humans solve this task partly by calculating transitional probabilities between sounds. Behavioral and ERP studies suggest that detection of sequential probabilities (statistical learning) plays an important role in the process of word segmentation. To identify the brain regions that are engaged during statistical segmentation of tone sequences, we measured changes in blood oxygenation using multichannel near-infrared spectroscopy (NIRS) while participants were exposed to continuous, nonlinguistic auditory sequences, the elements of which were organized into fixed "tone-words," but sequenced in random order. We habituated the participants to the tone-words by presenting the stimuli in a training phase prior to the presentation of the continuous tone sequences. After training, the statistical sequences, which included six tone-words, and the random sequences, which included 11 tones in random order, were presented alternately during NIRS recording. A large increase in the oxygenated hemoglobin concentration was observed in the left inferior frontal cortex (IFC) during the statistical sequence condition, but not during the random sequence condition. This suggests that the left IFC plays an important role in statistical segmentation of tone sequences, during which participants deploy the knowledge obtained in the training phase on the subsequent continuous sequence.
Population Coding of Song Element Sequence in the Bengalese Finch HVC
Birdsong is a complex vocalization composed of various song elements organized according to sequential rules. Two alternative views exist that explain the neural representation of song element sequences in the songbird brain. The finding of sequential selective neurons supports the idea that the song element sequence is encoded in a chain of rigid selective neurons. Alternatively, song structure could be encoded in an ensemble of relatively broad selective neurons arranged in a distributed manner. Here we attempted to determine which neural representation actually occurs in the song system by recording neural responses to various stimuli and performing information-theoretic analysis on the data obtained. We recorded the neural responses to all possible element pairs of stimuli in the Bengalese finch brain nucleus high vocal centre (HVC). Our results showed that each neuron has broad but differential response properties to element sequences beyond the structure of self-generated song. To quantify the transmitted information by such a broadly tuned neural population, we calculated the time course of mutual information between auditory stimuli and neural activities. Confounded information, which represents the relationship between present and previous elements, increased significantly immediately after stimulus presentation. These results indicate that the song element sequence is encoded in a neural ensemble in the HVC via population coding. These findings give us a new encoding scheme for the song element sequence using a distributed neural representation rather than the chain model of rigid selective neurons.
Vocal Control Area-related Expression of Neuropilin-1, Plexin-A4, and the Ligand Semaphorin-3A Has Implications for the Evolution of the Avian Vocal System
The avian vocal system is a good model for exploring the molecular basis of neural circuit evolution related to behavioral diversity. Previously, we conducted a comparative gene expression analysis among two different families of vocal learner, the Bengalese finch (Lonchura striata var. domestica), a songbird, and the budgerigar (Melopsittacus undulatus), a parrot; and a non-learner, the quail (Coturnix coturnix), to identify various axon guidance molecules such as cadherin and neuropilin-1 as vocal control area-related genes. Here, we continue with this study and examine the expression of neuropilin and related genes in these species in more detail. We found that neuropilin-1 and its coreceptor, plexin-A4, were expressed in several vocal control areas in both Bengalese finch and budgerigar brains. In addition, semaphorin-3A, the ligand of neuropilin-1, expression was not detected in vocal control areas in both species. Furthermore, there was some similar gene expression in the quail brain. These results suggest the possibility that a change in the expression of a combination of semaphorin/neuropilin/plexin was involved in the acquisition of vocal learning ability during evolution.
Evolution and Diversity in Avian Vocal System: an Evo-Devo Model from the Morphological and Behavioral Perspectives
Birds use various vocalizations to mark their territory and attract mates. Three groups of birds (songbirds, parrots, and hummingbirds) learn their vocalizations through imitation. In the brain of such vocal learners, there is a neural network called the song system specialized for vocal learning and production. In contrast, birds such as chickens and pigeons do not have such a neural network and can only produce innate sounds. Since each avian species shows distinct, genetically inherited vocal learning abilities that are related to its morphology, the avian vocal system is a good model for studying the evolution of functional neural circuits. Nevertheless, studies on avian vocalization from an evolutionary developmental-biological (Evo-Devo) perspective are scant. In the present review, we summarize the results of songbird studies and our recent work that used the Evo-Devo approach to understand the evolution of the avian vocal system.
Visual Statistical Learning of Shape Sequences: an ERP Study
Behavioral experiments have found that infants and adults learn statistically defined patterns presented in auditory and visual input sequences in the same manner regardless of whether the input was linguistic (syllables) or nonlinguistic (tones and shapes). In order do determine the time course and neural processes involved in online word segmentation and statistical learning of visual sequence, we recorded event-related potentials (ERPs) while participants were exposed to continuous sequences with elements organized into shape-words randomly connected to each other. After viewing three 6.6min sessions of sequences, the participants performed a behavioral choice test. The participants were divided into two groups (high and low learners) based on their behavioral performance. The overall mean performance was 72.2%, indicating that the shape sequence was segmented and that the participants learned the shape-triplets statistically. Grand-averaged ERPs showed that triplet-onset (the initial shapes of shape-words) elicited larger N400 amplitudes than did middle and final shapes embedded in continuous streams during the early learning sessions of high learners, but no triplet-onset effect was found among low learners. The results suggested that the N400 effect indicated online segmentation of the visual sequence and the degree of statistical learning. Our results also imply that statistical learning represents a common learning device.
Optimal Node Perturbation in Linear Perceptrons with Uncertain Eligibility Trace
Node perturbation learning has been receiving much attention as a method for achieving stochastic gradient descent. As it does not require direct gradient calculations, it can be applied to a reinforcement learning framework. However, in conventional node perturbation learning, the residual error due to perturbation is not eliminated even after convergence. Using infinitesimal perturbations suppresses the residual error, but such perturbations are less robust against uncertainty and noise in an eligibility trace, which is a memory of perturbation and input. We derive an optimal parameter schedule for node perturbation learning used with linear perceptrons with uncertainty in the eligibility trace. Our adaptive learning rule resolves the trade-off between robustness against the uncertainty and residual error reduction. The results obtained will be useful in designing learning rules and interpreting related biological knowledge.
Perceptual Chunking in the Self-produced Songs of Bengalese Finches (Lonchura Striata Var. Domestica)
Like humans, songbirds, including Bengalese finches, have hierarchical structures in their vocalizations. When humans perceive a sentence, processing occurs in phrase units, not words. In this study, we investigated whether songbirds also perceive their songs by chunks (clusters of song notes) rather than single song notes. We trained male Bengalese finches to react to a short noise in a Go/NoGo task. We then superimposed the noise onto recordings of their own songs and examined whether the reaction time was affected by the location of the short noise, that is, whether the noise was placed between chunks or in the middle of a chunk. The subjects' reaction times to the noise in the middle of a chunk were significantly longer than those to the noise placed between chunks. This result was not observed, however, when the songs were played in reverse. We thus concluded that Bengalese finches perceive their songs by chunks rather than single notes.
Potential Role of Monkey Inferior Parietal Neurons Coding Action Semantic Equivalences As Precursors of Parts of Speech
The anterior portion of the inferior parietal cortex possesses comprehensive representations of actions embedded in behavioural contexts. Mirror neurons, which respond to both self-executed and observed actions, exist in this brain region in addition to those originally found in the premotor cortex. We found that parietal mirror neurons responded differentially to identical actions embedded in different contexts. Another type of parietal mirror neuron represents an inverse and complementary property of responding equally to dissimilar actions made by itself and others for an identical purpose. Here, we propose a hypothesis that these sets of inferior parietal neurons constitute a neural basis for encoding the semantic equivalence of various actions across different agents and contexts. The neurons have mirror neuron properties, and they encoded generalization of agents, differentiation of outcomes, and categorization of actions that led to common functions. By integrating the activities of these mirror neurons with various codings, we further suggest that in the ancestral primates' brains, these various representations of meaningful action led to the gradual establishment of equivalence relations among the different types of actions, by sharing common action semantics. Such differential codings of the components of actions might represent precursors to the parts of protolanguage, such as gestural communication, which are shared among various members of a society. Finally, we suggest that the inferior parietal cortex serves as an interface between this action semantics system and other higher semantic systems, through common structures of action representation that mimic language syntax.
Identification of Gonadotropin-inhibitory Hormone in the Zebra Finch (Taeniopygia Guttata): Peptide Isolation, CDNA Cloning and Brain Distribution
Two novel RFamide peptides, kisspeptins and gonadotropin-inhibitory hormone (GnIH) are neuropeptides that appear critical in the regulation of the reproductive neuroendocrine axis. GnIH was first identified in avian brain, however, kisspeptins have not been identified in birds. To determine biochemically the presence of kisspeptins and GnIH in the zebra finch, a study was conducted to isolate these two peptides from zebra finch brain. Peptides were isolated by immunoaffinity purification and only one peptide was characterized by mass spectrometry. This peptide was confirmed to be a 12-amino acid sequence with RFamide at its C-terminus; its sequence is SIKPFSNLPLRFamide (zebra finch GnIH). By this approach, however, identification of kisspeptin from zebra finch brain was not achieved. Cloned zebra finch GnIH precursor cDNA encoded three peptides that possess characteristic LPXRFamide (X=L or Q) motifs at the C-termini. In situ hybridization and immunohistochemical analysis revealed the cellular localization of zebra finch GnIH mRNA and peptide in the paraventricular nucleus and the dorsomedial nucleus of the hypothalamus. Fluorescent immunohistochemistry with confocal microscopy indicated that GnIH-immunoreactive (ir) fibers are very close appositions with gonadotropin-releasing hormone-I (GnRH-I) cells. Furthermore GnIH-ir nerve fibers were widely distributed in the multiple brain regions including the septum, preoptic area, median eminence, optic tectum and median eminence. The prominent fibers were seen in the ventral tegmental area, midbrain central gray and dorsal motor nucleus of the vagus in the medulla. Thus, GnIH may participate in not only neuroendocrine functions but also regulation of motivation for social behavior and autonomic mechanisms.
Extracting State Transition Dynamics from Multiple Spike Trains Using Hidden Markov Models with Correlated Poisson Distribution
Neural activity is nonstationary and varies across time. Hidden Markov models (HMMs) have been used to track the state transition among quasi-stationary discrete neural states. Within this context, an independent Poisson model has been used for the output distribution of HMMs; hence, the model is incapable of tracking the change in correlation without modulating the firing rate. To achieve this, we applied a multivariate Poisson distribution with correlation terms for the output distribution of HMMs. We formulated a variational Bayes (VB) inference for the model. The VB could automatically determine the appropriate number of hidden states and correlation types while avoiding the overlearning problem. We developed an efficient algorithm for computing posteriors using the recursive relationship of a multivariate Poisson distribution. We demonstrated the performance of our method on synthetic data and real spike trains recorded from a songbird.
Song Memory in Female Birds: Neuronal Activation Suggests Phonological Coding
Male Bengalese finches sing complex song sequences during courtship. To examine the female perception of sequence complexity, we tested female auditory processing with respect to sequential differences in the caudomedial nidopallium and caudomedial mesopallium. Repeated song presentations caused lower expression of the immediate early gene ZENK; however, consecutive presentation of a new song reinduced full ZENK expression. We presented a sequence-shuffled version of the father's song after repeated presentation of the original (unmodified) father's song. The shuffled songs caused lower ZENK expression in both the caudomedial nidopallium and caudomedial mesopallium. Although phonological differences caused full ZENK expression, sequential differences in song elements did not induce ZENK expression. Thus, it appears that female song perception is based on phonological, rather than sequential, information.
Music Playing and Memory Trace: Evidence from Event-related Potentials
We examined the relationship between motor practice and auditory memory for sound sequences to evaluate the hypothesis that practice involving physical performance might enhance auditory memory. Participants learned two unfamiliar sound sequences using different training methods. Under the key-press condition, they learned a melody while pressing a key during auditory input. Under the no-key-press condition, they listened to another melody without any key pressing. The two melodies were presented alternately, and all participants were trained in both methods. Participants were instructed to pay attention under both conditions. After training, they listened to the two melodies again without pressing keys, and ERPs were recorded. During the ERP recordings, 10% of the tones in these melodies deviated from the originals. The grand-average ERPs showed that the amplitude of mismatch negativity (MMN) elicited by deviant stimuli was larger under the key-press condition than under the no-key-press condition. This effect appeared only in the high absolute pitch group, which included those with a pronounced ability to identify a note without external reference. This result suggests that the effect of training with key pressing was mediated by individual musical skills.
Molecular Characterization of the Song Control Nucleus HVC in Bengalese Finch Brain
Songbirds have a specialized neural substrate for learned vocalization, called the song circuit, which consists of several song nuclei in the brain. The song control nucleus HVC (a letter-based name) is the intersection point of the song learning and vocal motor pathways. Knowledge of the types of genes expressed in the HVC is essential in understanding the molecular aspects of the HVC. Gene expression in the HVC under silent conditions shows the competence necessary for singing. To investigate this, we compared the HVC with its adjacent tissues in searching for the molecular specificities of the song nucleus HVC using an in-house cDNA microarray of the Bengalese finch (Lonchura striata var. domestica). Our microarray analysis revealed that 70 genes were differentially expressed in the HVC compared with the adjacent tissue. We investigated 27 of the microarray-selected genes that were enriched or repressed in the HVC by in situ hybridization. We found that multiple calcium-binding proteins (e.g., CAPS2, parvalbumin and ATH) were enriched in the HVC. Meanwhile, the adult HVC showed low expression levels of plasticity-related genes (e.g., CAMK2A and MAP2K1) compared with the juvenile HVC. The HVC plays an important role during song learning, but our results suggest that the plasticity of this nucleus may be suppressed during adulthood. Our findings provide new information about the molecular features that characterize the HVC.
Twitter Evolution: Converging Mechanisms in Birdsong and Human Speech
Vocal imitation in human infants and in some orders of birds relies on auditory-guided motor learning during a sensitive period of development. It proceeds from 'babbling' (in humans) and 'subsong' (in birds) through distinct phases towards the full-fledged communication system. Language development and birdsong learning have parallels at the behavioural, neural and genetic levels. Different orders of birds have evolved networks of brain regions for song learning and production that have a surprisingly similar gross anatomy, with analogies to human cortical regions and basal ganglia. Comparisons between different songbird species and humans point towards both general and species-specific principles of vocal learning and have identified common neural and molecular substrates, including the forkhead box P2 (FOXP2) gene.
Evaluation of Pax6 Mutant Rat As a Model for Autism
Autism is a highly variable brain developmental disorder and has a strong genetic basis. Pax6 is a pivotal player in brain development and maintenance. It is expressed in embryonic and adult neural stem cells, in astrocytes in the entire central nervous system, and in neurons in the olfactory bulb, amygdala, thalamus, and cerebellum, functioning in highly context-dependent manners. We have recently reported that Pax6 heterozygous mutant (rSey(2)/+) rats with a spontaneous mutation in the Pax6 gene, show impaired prepulse inhibition (PPI). In the present study, we further examined behaviors of rSey(2)/+ rats and revealed that they exhibited abnormality in social interaction (more aggression and withdrawal) in addition to impairment in rearing activity and in fear-conditioned memory. Ultrasonic vocalization (USV) in rSey(2)+ rat pups was normal in male but abnormal in female. Moreover, treatment with clozapine successfully recovered the defects in sensorimotor gating function, but not in fear-conditioned memory. Taken together with our prior human genetic data and results in other literatures, rSey(2)/+ rats likely have some phenotypic components of autism.
Hippocampus Lesions Induced Deficits in Social and Spatial Recognition in Octodon Degus
Previous studies of rodents reported that the hippocampus plays an important role in social behavior as well as spatial behavior. However, there are inconsistencies between reports of the effects of hippocampal lesions on social behavior. The present study sought to clarify the aspects of social behavior in which the hippocampus plays a role in the degu, Octodon degus, a social rodent. We examined the effects of hippocampal lesions on social behavior in the degu using familiar and novel partners. When placed in a familiar environment with a familiar partner after surgery, sham operation control (S.Cont) degus exhibited affinitive behavior longer compared with hippocampal lesioned (HPC) degus. In a novel environment, S.Cont degus exhibited longer aggressive behavior toward novel partners, and longer affinitive behavior with familiar partners compared with HPC degus. HPC degus did not show evidence of differentiation in social behavior, regardless of partner's novelty. The results of an anxiety test confirmed that these findings could not be attributed to changes in emotional state. We conducted an object-recognition test with the same subjects. HPC degus showed an impairment in spatial recognition but not object recognition. Taken together, these results suggest that the degu hippocampus plays an important role not only in spatial recognition but also social recognition. The changes in social behavior resulting from hippocampal lesions were interpreted as due to an impairment of social recognition rather than an impairment in novelty detection.
Songs to Syntax: the Linguistics of Birdsong
Unlike our primate cousins, many species of bird share with humans a capacity for vocal learning, a crucial factor in speech acquisition. There are striking behavioural, neural and genetic similarities between auditory-vocal learning in birds and human infants. Recently, the linguistic parallels between birdsong and spoken language have begun to be investigated. Although both birdsong and human language are hierarchically organized according to particular syntactic constraints, birdsong structure is best characterized as 'phonological syntax', resembling aspects of human sound structure. Crucially, birdsong lacks semantics and words. Formal language and linguistic analysis remains essential for the proper characterization of birdsong as a model system for human speech and language, and for the study of the brain and cognition evolution.
Cross Fostering Experiments Suggest That Mice Songs Are Innate
Vocal learning is a central functional constituent of human speech, and recent studies showing that adult male mice emit ultrasonic sound sequences characterized as "songs" have suggested that the ultrasonic courtship sounds of mice provide a mammalian model of vocal learning.
Expression Pattern of Cadherins in the Naked Mole Rat (Heterocephalus Glaber) Suggests Innate Cortical Diversification of the Cerebrum
The cerebral cortex is an indispensable region for higher cognitive function that is remarkably diverse among mammalian species. Although previous research has shown that the cortical area map in the mammalian cerebral cortex is formed by innate and activity-dependent mechanisms, it remains unknown how these mechanisms contribute to the evolution and diversification of the functional cortical areas in various species. The naked mole rat (Heterocephalus glaber) is a subterranean, eusocial rodent. Physiological and anatomical studies have revealed that the visual system is regressed and the somatosensory system is enlarged. To examine whether species differences in cortical area development are caused by intrinsic factors or environmental factors, we performed comparative gene expression analysis of neonatal naked mole rat and mouse brains. The expression domain of cadherin-6, a somatosensory marker, was expanded caudally and shifted dorsally in the cortex, whereas the expression domain of cadherin-8, a visual marker, was reduced caudally in the neonatal naked mole rat cortex. The expression domain of cadherin-8 was also reduced in other visual areas, such as the lateral geniculate nucleus and superior colliculus. Immunohistochemical analysis of thalamocortical fibers further suggested that somatosensory input did not affect cortical gene expression in the neonatal naked mole rat brain. These results suggest that the development of the somatosensory system and the regression of the visual system in the naked mole rat cortex are due to intrinsic genetic mechanisms as well as sensory input-dependent mechanisms. Intrinsic genetic mechanisms thus appear to contribute to species diversity in cortical area formation.
Comparative Gene Expression Analysis Among Vocal Learners (bengalese Finch and Budgerigar) and Non-learners (quail and Ring Dove) Reveals Variable Cadherin Expressions in the Vocal System
Birds use various vocalizations to communicate with one another, and some are acquired through learning. So far, three families of birds (songbirds, parrots, and hummingbirds) have been identified as having vocal learning ability. Previously, we found that cadherins, a large family of cell-adhesion molecules, show vocal control-area-related expression in a songbird, the Bengalese finch. To investigate the molecular basis of evolution in avian species, we conducted comparative analysis of cadherin expressions in the vocal and other neural systems among vocal learners (Bengalese finch and budgerigar) and a non-learner (quail and ring dove). The gene expression analysis revealed that cadherin expressions were more variable in vocal and auditory areas compared to vocally unrelated areas such as the visual areas among these species. Thus, it appears that such diverse cadherin expressions might have been related to generating species diversity in vocal behavior during the evolution of avian vocal learning.
Cooperation of Deterministic Dynamics and Random Noise in Production of Complex Syntactical Avian Song Sequences: a Neural Network Model
How the brain learns and generates temporal sequences is a fundamental issue in neuroscience. The production of birdsongs, a process which involves complex learned sequences, provides researchers with an excellent biological model for this topic. The Bengalese finch in particular learns a highly complex song with syntactical structure. The nucleus HVC (HVC), a premotor nucleus within the avian song system, plays a key role in generating the temporal structures of their songs. From lesion studies, the nucleus interfacialis (NIf) projecting to the HVC is considered one of the essential regions that contribute to the complexity of their songs. However, the types of interaction between the HVC and the NIf that can produce complex syntactical songs remain unclear. In order to investigate the function of interactions between the HVC and NIf, we have proposed a neural network model based on previous biological evidence. The HVC is modeled by a recurrent neural network (RNN) that learns to generate temporal patterns of songs. The NIf is modeled as a mechanism that provides auditory feedback to the HVC and generates random noise that feeds into the HVC. The model showed that complex syntactical songs can be replicated by simple interactions between deterministic dynamics of the RNN and random noise. In the current study, the plausibility of the model is tested by the comparison between the changes in the songs of actual birds induced by pharmacological inhibition of the NIf and the changes in the songs produced by the model resulting from modification of parameters representing NIf functions. The efficacy of the model demonstrates that the changes of songs induced by pharmacological inhibition of the NIf can be interpreted as a trade-off between the effects of noise and the effects of feedback on the dynamics of the RNN of the HVC. These facts suggest that the current model provides a convincing hypothesis for the functional role of NIf-HVC interaction.
Type-II Cadherins Modulate Neural Activity in Cultured Rat Hippocampal Neurons
Cadherins, cell adhesion molecules widely expressed in the nervous system, are thought to be involved in synapse formation and function. To explore the role of cadherins in neuronal activity, we performed electrophysiological and morphological analyses of rat hippocampal cultured neurons overexpressing type-II cadherins, such as cadherin-6B and cadherin-7. We found that cadherin-6B increased but cadherin-7 decreased the number of protrusions of dendritic spines, and affected the frequency of miniature excitatory postsynaptic currents. Our results suggest that type-II cadherins may modulate neural activity by regulating neuronal morphology.
Statistical Mechanics of Structural and Temporal Credit Assignment Effects on Learning in Neural Networks
Neural networks can learn flexible input-output associations by changing their synaptic weights. The representational performance and learning dynamics of neural networks are intensively studied in several fields. Neural networks face the "credit assignment problem" in situations in which only incomplete performance evaluations are available. The credit assignment problem is that a network should assign credit or blame for its behaviors according to the contribution to the network performance. In reinforcement learning, a scalar evaluation signal is delivered to a network. The two main types of credit assignment problems in reinforcement learning are structural and temporal, that is, which parameters of the network (structural) and which past network activities (temporal) are related to an evaluation signal given from an environment. In this study, we apply statistical mechanical analysis to the learning processes in a simple neural network model to clarify the effects of two kinds of credit assignments and their interactions. Our model is based on node perturbation learning with eligibility trace. Node perturbation is a stochastic gradient learning method that can solve structural credit assignment problems by introducing a perturbation into the system output. The eligibility trace preserves the past network activities with a temporal credit to deal with the delay of an instruction signal. We show that both credit assignment effects mutually interact and the optimal time constant of the eligibility trace varies not only for the evaluation delay but also the network size.
Categorical and Dimensional Perceptions in Decoding Emotional Facial Expressions
We investigated whether categorical perception and dimensional perception can co-occur while decoding emotional facial expressions. In Experiment 1, facial continua with endpoints consisting of four basic emotions (i.e., happiness-fear and anger-disgust) were created by a morphing technique. Participants rated each facial stimulus using a categorical strategy and a dimensional strategy. The results show that the happiness-fear continuum was divided into two clusters based on valence, even when using the dimensional strategy. Moreover, the faces were arrayed in order of the physical changes within each cluster. In Experiment 2, we found a category boundary within other continua (i.e., surprise-sadness and excitement-disgust) with regard to the arousal and valence dimensions. These findings indicate that categorical perception and dimensional perception co-occurred when emotional facial expressions were rated using a dimensional strategy, suggesting a hybrid theory of categorical and dimensional accounts.
On-line Statistical Segmentation of a Non-speech Auditory Stream in Neonates As Demonstrated by Event-related Brain Potentials
The ability to statistically segment a continuous auditory stream is one of the most important preparations for initiating language learning. Such ability is available to human infants at 8 months of age, as shown by a behavioral measurement. However, behavioral study alone cannot determine how early this ability is available. A recent study using measurements of event-related potential (ERP) revealed that neonates are able to detect statistical boundaries within auditory streams of speech syllables. Extending this line of research will allow us to better understand the cognitive preparation for language acquisition that is available to neonates. The aim of the present study was to examine the domain-generality of such statistical segmentation. Neonates were presented with nonlinguistic tone sequences composed of four tritone units, each consisting of three semitones extracted from one octave, for two 5-minute sessions. Only the first tone of each unit evoked a significant positivity in the frontal area during the second session, but not in the first session. This result suggests that the general ability to distinguish units in an auditory stream by statistical information is activated at birth and is probably innately prepared in humans.
Complex Sequencing Rules of Birdsong Can Be Explained by Simple Hidden Markov Processes
Complex sequencing rules observed in birdsongs provide an opportunity to investigate the neural mechanism for generating complex sequential behaviors. To relate the findings from studying birdsongs to other sequential behaviors such as human speech and musical performance, it is crucial to characterize the statistical properties of the sequencing rules in birdsongs. However, the properties of the sequencing rules in birdsongs have not yet been fully addressed. In this study, we investigate the statistical properties of the complex birdsong of the Bengalese finch (Lonchura striata var. domestica). Based on manual-annotated syllable labeles, we first show that there are significant higher-order context dependencies in Bengalese finch songs, that is, which syllable appears next depends on more than one previous syllable. We then analyze acoustic features of the song and show that higher-order context dependencies can be explained using first-order hidden state transition dynamics with redundant hidden states. This model corresponds to hidden Markov models (HMMs), well known statistical models with a large range of application for time series modeling. The song annotation with these models with first-order hidden state dynamics agreed well with manual annotation, the score was comparable to that of a second-order HMM, and surpassed the zeroth-order model (the Gaussian mixture model; GMM), which does not use context information. Our results imply that the hierarchical representation with hidden state dynamics may underlie the neural implementation for generating complex behavioral sequences with higher-order dependencies.
A Direct Neuronal Connection Between the Telencephalic Nucleus Robustus Arcopallialis and the Nucleus Nervi Hypoglossi, Pars Tracheosyringealis in Bengalese Finches (Lonchura Striata Var. Domestica)
Bird species with vocal learning possess a projection from the telencephalic nucleus to the nucleus nervi hypoglossi, pars tracheosyringealis (XIIts) in the medulla, where a final common pathway that controls the vocal organ, i.e., the synrinx, originates. The anatomical basis of this projection has not been well investigated in one species of songbird, the Bengalese finch (Lonchura striata var. domestica). The present study used anterograde and retrograde tracing experiments to examine and describe this projection in Bengalese finches. Following iontophoretic injections of biotinylated dextran amine into the telencephalic nucleus robustus arcopallialis (RA), we detected anterograde-labeled terminations in the XIIts. In addition, labeled terminals were seen in other vocal-respiratory-related nuclei, such as the dorsomedial nucleus of the nucleus intercollicularis, nucleus infraolivaris superior, nucleus of the rostral ventrolateral medulla, nucleus parambigualis, nucleus ambiguous, and nucleus retroambigualis. Furthermore, following injections into the XIIts, we detected retrograde-labeled cell bodies scattered throughout the ipsilateral RA. The present results revealed that the direct projections of the RA to the XIIts in male Bengalese finches are similar to those in other songbirds with vocal learning abilities.
Dynamic Expression of Cadherins Regulates Vocal Development in a Songbird
Since, similarly to humans, songbirds learn their vocalization through imitation during their juvenile stage, they have often been used as model animals to study the mechanisms of human verbal learning. Numerous anatomical and physiological studies have suggested that songbirds have a neural network called 'song system' specialized for vocal learning and production in their brain. However, it still remains unknown what molecular mechanisms regulate their vocal development. It has been suggested that type-II cadherins are involved in synapse formation and function. Previously, we found that type-II cadherin expressions are switched in the robust nucleus of arcopallium from cadherin-7-positive to cadherin-6B-positive during the phase from sensory to sensorimotor learning stage in a songbird, the Bengalese finch. Furthermore, in vitro analysis using cultured rat hippocampal neurons revealed that cadherin-6B enhanced and cadherin-7 suppressed the frequency of miniature excitatory postsynaptic currents via regulating dendritic spine morphology.
Sequential Learning and Rule Abstraction in Bengalese Finches
The Bengalese finch (Lonchura striata var. domestica) is a species of songbird. Males sing courtship songs with complex note-to-note transition rules, while females discriminate these songs when choosing their mate. The present study uses serial reaction time (RT) to examine the characteristics of the Bengalese finches' sequential behaviours beyond song production. The birds were trained to produce the sequence with an "A-B-A" structure. After the RT to each key position was determined to be stable, we tested the acquisition of the trained sequential response by presenting novel and random three-term sequences (random test). We also examined whether they could abstract the embedded rule in the trained sequence and apply it to the novel test sequence (abstract test). Additionally, we examined rule abstraction through example training by increasing the number of examples in baseline training from 1 to 5. When considered as (gender) groups, training with 5 examples resulted in no statistically significant differences in the abstract tests, while statistically significant differences were observed in the random tests, suggesting that the male birds learned the trained sequences and transferred the abstract structure they had learned during the training trials. Individual data indicated that males, as opposed to females, were likely to learn the motor pattern of the sequence. The results are consistent with observations that males learn to produce songs with complex sequential rules, whereas females do not.
Comparative Analysis of Mineralocorticoid Receptor Expression Among Vocal Learners (Bengalese Finch and Budgerigar) and Non-vocal Learners (quail and Ring Dove) Has Implications for the Evolution of Avian Vocal Learning
Mineralocorticoid receptor is the receptor for corticosteroids such as corticosterone or aldosterone. Previously, we found that mineralocorticoid receptor was highly expressed in song nuclei of a songbird, Bengalese finch (Lonchura striata var. domestica). Here, to examine the relationship between mineralocorticoid receptor expression and avian vocal learning, we analyzed mineralocorticoid receptor expression in the developing brain of another vocal learner, budgerigar (Melopsittacus undulatus) and non-vocal learners, quail (Coturnix japonica) and ring dove (Streptopelia capicola). Mineralocorticoid receptor showed vocal control area-related expressions in budgerigars as Bengalese finches, whereas no such mineralocorticoid receptor expressions were seen in the telencephalon of non-vocal learners. Thus, these results suggest the possibility that mineralocorticoid receptor plays a role in vocal development of parrots as songbirds and that the acquisition of mineralocorticoid receptor expression is involved in the evolution of avian vocal learning.
Decision-making Based on Emotional Images
The emotional outcome of a choice affects subsequent decision making. While the relationship between decision making and emotion has attracted attention, studies on emotion and decision making have been independently developed. In this study, we investigated how the emotional valence of pictures, which was stochastically contingent on participants' choices, influenced subsequent decision making. In contrast to traditional value-based decision-making studies that used money or food as a reward, the "reward value" of the decision outcome, which guided the update of value for each choice, is unknown beforehand. To estimate the reward value of emotional pictures from participants' choice data, we used reinforcement learning models that have successfully been used in previous studies for modeling value-based decision making. Consequently, we found that the estimated reward value was asymmetric between positive and negative pictures. The negative reward value of negative pictures (relative to neutral pictures) was larger in magnitude than the positive reward value of positive pictures. This asymmetry was not observed in valence for an individual picture, which was rated by the participants regarding the emotion experienced upon viewing it. These results suggest that there may be a difference between experienced emotion and the effect of the experienced emotion on subsequent behavior. Our experimental and computational paradigm provides a novel way for quantifying how and what aspects of emotional events affect human behavior. The present study is a first step toward relating a large amount of knowledge in emotion science and in taking computational approaches to value-based decision making.
Segmentation of Expiratory and Inspiratory Sounds in Baby Cry Audio Recordings Using Hidden Markov Models
The paper describes an application of machine learning techniques to identify expiratory and inspiration phases from the audio recording of human baby cries. Crying episodes were recorded from 14 infants, spanning four vocalization contexts in their first 12 months of age; recordings from three individuals were annotated manually to identify expiratory and inspiratory sounds and used as training examples to segment automatically the recordings of the other 11 individuals. The proposed algorithm uses a hidden Markov model architecture, in which state likelihoods are estimated either with Gaussian mixture models or by converting the classification decisions of a support vector machine. The algorithm yields up to 95% classification precision (86% average), and its ability generalizes over different babies, different ages, and vocalization contexts. The technique offers an opportunity to quantify expiration duration, count the crying rate, and other time-related characteristics of baby crying for screening, diagnosis, and research purposes over large populations of infants.
Node Perturbation Learning Without Noiseless Baseline
Node perturbation learning is a stochastic gradient descent method for neural networks. It estimates the gradient by comparing an evaluation of the perturbed output and the unperturbed output performance, which we call the baseline. Node perturbation learning has primarily been investigated without taking noise on the baseline into consideration. In real biological systems, however, neural activities are intrinsically noisy, and hence, the baseline is likely contaminated with the noise. In this paper, we propose an alternative learning method that does not require such a noiseless baseline. Our method uses a "second perturbation", which is calculated with different noise than the first perturbation. By comparing the evaluation of the outcomes with the first perturbation and with the second perturbation, the network weights are updated. We reveal that the learning speed showed only a linear decrease with the variance of the second perturbation. Moreover, using the second perturbation can lead to a decrease in residual error compared to the case of using the noiseless baseline.
Convergent Differential Regulation of Parvalbumin in the Brains of Vocal Learners
Spoken language and learned song are complex communication behaviors found in only a few species, including humans and three groups of distantly related birds--songbirds, parrots, and hummingbirds. Despite their large phylogenetic distances, these vocal learners show convergent behaviors and associated brain pathways for vocal communication. However, it is not clear whether this behavioral and anatomical convergence is associated with molecular convergence. Here we used oligo microarrays to screen for genes differentially regulated in brain nuclei necessary for producing learned vocalizations relative to adjacent brain areas that control other behaviors in avian vocal learners versus vocal non-learners. A top candidate gene in our screen was a calcium-binding protein, parvalbumin (PV). In situ hybridization verification revealed that PV was expressed significantly higher throughout the song motor pathway, including brainstem vocal motor neurons relative to the surrounding brain regions of all distantly related avian vocal learners. This differential expression was specific to PV and vocal learners, as it was not found in avian vocal non-learners nor for control genes in learners and non-learners. Similar to the vocal learning birds, higher PV up-regulation was found in the brainstem tongue motor neurons used for speech production in humans relative to a non-human primate, macaques. These results suggest repeated convergent evolution of differential PV up-regulation in the brains of vocal learners separated by more than 65-300 million years from a common ancestor and that the specialized behaviors of learned song and speech may require extra calcium buffering and signaling.
Birdsong Neurolinguistics: Songbird Context-free Grammar Claim is Premature
There are remarkable behavioral, neural, and genetic similarities between song learning in songbirds and speech acquisition in human infants. Previously, we have argued that this parallel cannot be extended to the level of sentence syntax. Although birdsong can indeed have a complex structure, it lacks the combinatorial complexity of human language syntax. Recently, this conclusion has been challenged by a report purporting to show that songbirds can learn so-called context-free syntactic rules and then use them to discriminate particular syllable patterns. Here, we demonstrate that the design of this study is inadequate to draw such a conclusion, and offer alternative explanations for the experimental results that do not require the acquisition and use of context-free grammar rules or a grammar of any kind, only the simpler hypothesis of acoustic similarity matching. We conclude that the evolution of vocal learning involves both neural homologies and behavioral convergence, and that human language reflects a unique cognitive capacity.
Statistical Mechanics of Reward-Modulated Learning in Decision-Making Networks
The neural substrates of decision making have been intensively studied using experimental and computational approaches. Alternative-choice tasks accompanying reinforcement have often been employed in investigations into decision making. Choice behavior has been empirically found in many experiments to follow Herrnstein's matching law. A number of theoretical studies have been done on explaining the mechanisms responsible for matching behavior. Various learning rules have been proved in these studies to achieve matching behavior as a steady state of learning processes. The models in the studies have consisted of a few parameters. However, a large number of neurons and synapses are expected to participate in decision making in the brain. We investigated learning behavior in simple but large-scale decision-making networks. We considered the covariance learning rule, which has been demonstrated to achieve matching behavior as a steady state (Loewenstein & Seung, 2006). We analyzed model behavior in a thermodynamic limit where the number of plastic synapses went to infinity. By means of techniques of the statistical mechanics, we can derive deterministic differential equations in this limit for the order parameters, which allow an exact calculation of the evolution of choice behavior. As a result, we found that matching behavior cannot be a steady state of learning when the fluctuations in input from individual sensory neurons are so large that they affect the net input to value-encoding neurons. This situation naturally arises when the synaptic strength is sufficiently strong and the excitatory input and the inhibitory input to the value-encoding neurons are balanced. The deviation from matching behavior is caused by increasing variance in the input potential due to the diffusion of synaptic efficacies. This effect causes an undermatching phenomenon, which has been often observed in behavioral experiments.
