Cerebral Cortex Organization

• Cognitive functions are carried out by the association cortices.

Cerebral Cortex Organization

• Neocortex is comprised of 6 layers.
• Cytoarchitectonic areas are subregions that are based on histological differences.
• Histological differences include the architecture of neurons and their processes and connections.
• Cytoarchitectonic areas vary among species and among individuals.
• The human brain can be divided into some 50 cytoarchitectonic areas based on histology.
• Cerebral cortex organized in layers containing paleocortex which has 3 layers.
• Neocortex has 6 layers.
• Archiocortex has 4 layers.
• Layers 6 & 5 include pyramidal neurons with exiting axons.
• Layer 4 includes stellate neurons with locally ramifying axons.
• Layers 3 & 2 include smaller pyramidal neurons with corticocortical connections.
• Layer 1 is mostly neuropil.
• Each cortical layer has a primary source of input and a primary output target.
• Each area has vertical columnar or radial connections.
• Interneurons give rise to extensive axons that extend horizontally within the cortex and link functionally similar groups of cells.
• Outputs are sent to major targets of each neocortical layer.
• Input comes from other cortical areas and the thalamus.
• Thalamic input goes to layers 4.
• Input from the brainstem modulates each layer.

Association Cortices Features

• Unique features for association cortices includes inputs via the thalamus (e.g., pulvinar, medial dorsal nucleus).
• This reflects sensory and motor information that has already been processed in the primary sensory and motor areas of the cerebral cortex.
• Enriched corticocortical and interhemispheric connections are also unique association cortices features.
• The same is true for subcortical connections (i.e., dopaminergic nuclei in midbrain, noradrenergic and serotonergic nuclei in the reticular formation, and cholinergic nuclei in the brainstem and basal forebrain).
• Connectivity patterns within the cerebral cortex have implications for behavioral and psychiatric disorders.
• Examples of these disorders include addiction, depression, attention deficit disorder, and psychoses.

Synesthesia

• Synesthesia involves the mixing of senses.
• People with synesthesia experience the world differently.
• The potential cause could be miswiring as new synaptic connections are established.

Parietal Association Cortex

• Parietal association cortex is related to attention and awareness.

Parietal Cortex

• Contralateral neglect syndrome involves the inability to attend to objects or even one's own body.
• This occurs in a certain space, despite intact visual acuity, somatic sensation, and motor ability, opposite the parietal lesion.
• Contralateral neglect syndrome is associated with damage to the right parietal cortex.
• Right parietal cortex mediates attention to both the right and left halves of the body and extrapersonal space.
• The left hemisphere mediates attention primarily to the right, serving language functions.
• Neurons in the parietal cortex are activated when an animal attends to a target, not when the same target is ignored.
• Balint's syndrome involves bilateral damage to the dorsal posterior parietal and lateral occipital cortex.
• Simultanagnosia includes the inability to perceive more than one visual object at a time.
• Optic ataxia involves difficulty in visually guided reaching.
• Ocular apraxia involves difficulty in voluntary scanning of visual scenes.
• In a simultagnosia test, patients take a piecemeal approach to interpreting the scene, stating isolated items instead of comprehending the global whole.

Temporal Association Cortex

• Temporal association cortex is related to recognition.
• Agnosias arise from temporal lobe damage resulting in difficulty in identifying, naming, and recognizing objects.
• Right temporal lesions lead to agnosia for faces and objects.
• Left temporal lesions result in difficulties with language-related material.
• Prosopagnosia arises from damage to the (right) inferotemporal cortex (ITC).
• Prosopagnosia results in the inability to recognize/identify faces.

Visual Agnosia

• Visual agnosia is an inability to recognize visual objects.
• Visual Agnosia is caused by damage to the inferior left temporal cortex (IT).
• A person retains the ability to copy visual stimuli.
• A person has an inability to interpret, understand, or assign meaning to objects.
• Inferior temporal cortex, particularly the right fusiform gyrus, mediates face recognition.

Frontal Association Cortex

• Frontal association cortex is related to planning and decision-making.
• Damage to the prefrontal cortex results in behavioral and social problems as well as acting inappropriately to certain social circumstances.
• Phineas Gage's case is a famous example of prefrontal cortex damage.
• Short term memory functions are located dorsolateral in the frontal lobe.
• Planning and social restraint function are located more in the ventromedial part.
• Subjects must retain information about the previous trial, and then use it to guide behavior on future trials in the Wisconsin Card Sorting Task
• Prefrontal cortex contributes to adaptive behavior.
• A delayed response task can be used to assess frontal lobe damage and determine whether short-term memory is intact.
• The animal has to remember where is food is placed during the delay when they use the delayed response task so that it can be used to get the reward.
• Some neurons in the prefrontal cortex are activated maximally during the delay period.