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Lecture 8

Lecture 8.docx

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Rutsuko Ito

Lecture 8 Synaptic organization of the neocortex (cerebral cortex / neocortex) Lecture overview Neocortex: Part of the cerebral cortex. There are three phylogenetic categories of the cerebral cortex: 1. Archicortex a. Hippocampus b. Oldest c. Composed of two layers 2. Paleocortex a. Olfactory cortex b. Old c. Three layers d. Olfaction related 3. Neocortex a. New b. Six layers c. Detailed perception d. Learning e. Intelligence f. Focus on neocortex Mammalian cerebral cortex 1. In lower mammals the cerebral cortex that overlies the limbic system is a simple, smooth structure 2. Higher mammals and humans have more folds and a well defined temporal lobe and a bigger frontal lobe Human neocortex: 1. Gyri / gyrus a. Convolution or bump b. Protruding rounded surfaces 2. Sulci / sulcus a. Valley between gyri 3. Fissure a. Very deep sulcus 4. Economy of space a. Increased surface area b. Decreased axonal distance Cross species homology of subdivisions Representation of sensory and motor information in cortex 1. Input: sensory cortex a. Contralateral input 2. Output: motor cortex a. Contralateral output Functional localisation - Brodmann's areas 1. Prefrontal cortex a. Planning b. Decision making c. Social skills d. Conscience e. Working memory 2. Primary motor cortex 3. Primary somatosensory cortex 4. Primary audiotry cortex 5. Associational cortical areas a. There are more associational cortical areas that receive information than primary areas Prefrontal cortex 1. Highest level of cortical hierarchy dedicated to memory, planning and execution of actions a. Dorsolateral prefrontal cortex i. Right hemisphere 1. Spatial working memory ii. Left hemisphere 1. Language 2. Literacy 3. Logic b. Ventromedial PFC + Orbitofrontal PFC i. Motivated decision making ii. Emotional and autonomic responses iii. Conscience iv. Morality v. Social skills The changing prefrontal cortex throughout lifespan 1. Developmentally, the PFC is one of the last structures in the brain to become fully myelinated 2. Post-natally, PFC does not reach functional maturation until 15-19 years old 3. After adolescences and through adult life, the cytoarchitecture of the human cortex remains relatively stable 4. At 70-80 years old  neuronal involution in PFC Phineas Gage - orbitofrontal leucotomy 1. Resulted in loss of inhibition in terms of personality Dorsolateral PFC and spatial working memory task Stimulus specific activity 1. A dorsolateral prefrontal neuron shows persistent activity that is tuned to a preferred location of a visual cue (spatially selective) 2. Slide 14 a. Upper diagram i. Rasters and cumulative spike histogram for a preferred cue b. Lower diagram i. Spatial tuning curve of delayed period activity Ventromedial PFC involvement during working memory 1. There is evidence that different PFC regions contribute to different types of working memory (domain specificity theory) Dorsalateral vs Ventromedial 1. Dorsal PFC = spatial working memory a. Dorsal stream = vision for action 2. Ventral PFC = object working memory a. Ventral stream = vision for perception 3. Facial working memory? Domain specificity theory 1. Pattern vs Spatial cue a. In both versions the response (saccade) was the same i. Therefore firing would not be related to movement 2. Ventral PFC neurons were more responsive to patterns during the delay period 3. Dorsal PFC neurons were more responsive to
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