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Hippocampus: A curved elevation of gray matter extending the entire length of the floor of the temporal horn of the lateral ventricle. The hippocampus, subiculum, and Dentate gyrus constitute the hippocampal formation. Sometimes authors include the Entorhinal cortex in the hippocampal formation.

Learning and Memory: The Remember-Know Task

JoVE 10212

Source: Laboratories of Jonas T. Kaplan and Sarah I. Gimbel—University of Southern California

Our experience of memory is varied and complex. Sometimes we remember events in vivid detail, while other times we may only have a vague sense of familiarity. Memory researchers have made a distinction between memories that are recollected…


Anterograde Amnesia

JoVE 10301

Source: Laboratories of Jonas T. Kaplan and Sarah I. Gimbel—University of Southern California

Anterograde amnesia is the loss of the ability to form new memories. This can be distinguished from retrograde amnesia, which is the loss of old memories. Anterograde amnesia can result from damage to structures in the brain that are…



JoVE 10852

The sense of smell is achieved through the activities of the olfactory system. It starts when an airborne odorant enters the nasal cavity and reaches olfactory epithelium (OE). The OE is protected by a thin layer of mucus, which also serves the purpose of dissolving more complex compounds into simpler chemical odorants. The size of the OE and the density of sensory neurons varies among species; in humans, the OE is only about 9-10 cm2. The olfactory receptors are embedded in the cilia of the olfactory sensory neurons. Each neuron expresses only one type of olfactory receptor. However, each type of olfactory receptor is broadly tuned and can bind to multiple different odorants. For example, if receptor A binds to odorants 1 and 2, receptor B may bind to odorants 2 and 3, while receptor C binds to odorants 1 and 3. Thus, the detection and identification of an odor depend on the combination of olfactory receptors that recognize the odor; this is called combinatorial diversity. Olfactory sensory neurons are bipolar cells with a single long axon that sends olfactory information up to the olfactory bulb (OB). The OB is a part of the brain that is separated from the nasal cavity by the cribriform plate. Because of this convenient proximity between the nose and brain, the development of nasal drug applications is widely studied, especially in cases

 Core: Biology

Long-term Depression

JoVE 10847

Long-term depression, or LTD, is one of the ways by which synaptic plasticity—changes in the strength of chemical synapses—can occur in the brain. LTD is the process of synaptic weakening that occurs over time between pre and postsynaptic neuronal connections. The synaptic weakening of LTD works in opposition to synaptic strengthening by long-term potentiation (LTP) and together are the main mechanisms that underlie learning and memory. If over time, all synapses are maximally strengthened through LTP or some other mechanism, the brain would plateau in efficiency making learning and forming new memories difficult. LTD is a way to prune weaker synapses thereby freeing up resources and putting flexibility back into the central nervous system. One mechanism by which LTD occurs depends on the number of calcium ions in the postsynaptic neuron after presynaptic stimulation. Infrequent or low levels of presynaptic stimulation lead to low calcium ion influx and consequently, low calcium ion concentration in the postsynaptic neuron. The low calcium ion concentration initiates a signaling cascade that culminates in the endocytosis or removal of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) glutamate receptors from the plasma membrane. As a result, the postsynaptic response to the same sporadic presynaptic stimulation is further wea

 Core: Biology

What is a Nervous System?

JoVE 10838

The nervous system is the collection of specialized cells responsible for maintaining an organism’s internal environment and coordinating the interaction of an organism with the external world—from the control of essential functions such as heart rate and breathing to the movement needed to escape danger.

The vertebrate nervous system is divided into two major parts: the central nervous system (CNS) and the peripheral nervous system (PNS). The CNS includes the brain, spinal cord, and retina—the sensory tissue of the visual system. The PNS contains the sensory receptor cells for all of the other sensory systems—such as the touch receptors in the skin—as well as the nerves that carry information between the CNS and the rest of the body. Additionally, part of both the CNS and PNS contribute to the autonomic nervous system (also known as the visceral motor system). The autonomic nervous system controls smooth muscles, cardiac muscles, and glands that govern involuntary actions, such as digestion. The vertebrate brain is primarily divided into the cerebrum, cerebellum, and brainstem. The cerebrum is the largest, most anterior part of the brain that is divided into left and right hemispheres. Each hemisphere is further divided into four lobes: frontal, parietal, occipital, and temporal. The outermost layer of the cerebrum is called

 Core: Biology

Enzyme-linked Receptors

JoVE 10723

Enzyme-linked receptors are proteins which act as both receptor and enzyme, activating multiple intracellular signals. This is a large group of receptors that include the receptor tyrosine kinase (RTK) family. Many growth factors and hormones bind to and activate the RTKs.

RTKs are also called neurotrophin (NT) receptors because they bind nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), NT-3, NT-4/5, NT-6, and NT-7. The growth factors typically bind to an RTK subfamily of tropomyosin-related kinase receptors (Trk): Trk A, Trk B, and Trk C. Trk A is specific for NGF, NT-6, and NT-7. Trk B binds BDNF and NT-4/5, while Trk C is specific for NT-3. NT-3 can also bind with low affinity to Trk A and TrkB. The Trk receptors have a single transmembrane domain, with a growth factor binding site on the extracellular portion and an enzyme activation site intracellularly. Trk receptors can be monomeric or dimerized, where two Trk receptors are bound together. To activate the receptor, a single growth factor molecule either binds two monomeric receptors, causing them to dimerize, or it binds both sites on a pre-dimerized receptor. Once the receptors are bound, the tyrosines phosphorylate by pulling phosphates from ATP and donating them to each other, a process called “autophosphorylation.” This opens docking sites along the i

 Core: Biology

Motor Learning in Mirror Drawing

JoVE 10064

Source: Laboratory of Jonathan Flombaum—Johns Hopkins University

Colloquially, the terms learning and memory encompass a broad range of behaviors and mental systems, everything from learning to tie a shoe to mastering calculus (and a lot in between). Experimental psychologists have divided up…

 Cognitive Psychology
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