Cognition and Brain Structure Overview

Cognition and Brain Structure

• Cognition is the mental process of acquiring knowledge and understanding, involving memory, attention, language, problem-solving, and planning.
• Brain regions integrate information from different areas, including emotional processing and cortical regions.

Brodmann's Cortical Subdivisions

• Brodmann categorized early cortical regions based on cytoarchitecture (cellular structure).
• Newer methods now use finer divisions considering lamination, cell density, and connectivity.

Classical Cortical Structure (Mammalian)

• The mammalian neocortex typically shows six layers.
• Pyramidal cells are the main excitatory neuron type in the deep and superficial layers with their dendrites and axons projecting within or outside the cortex.

Cortical Layers

• Layer 1: Composed mainly of axons and interneurons.
• Layers 2 & 3: Contain pyramidal cells whose axons project to other cortical areas or to subcortical regions (white matter).
• Layer 4: Receives sensory input mainly from the thalamus, containing stellate cells.
• Layer 5: Contains large pyramidal cells, receiving inputs from layers 1-4, projecting to subcortical structures (e.g., brainstem and spinal cord).
• Layer 6: Contains small pyramidal neurons, projecting back to the thalamus.

Pyramidal Cell Function

• Pyramidal cells integrate and compare various inputs.

Stellate Cell Function

• Stellate cells have dendrites primarily located in layer 4.

Cortical Lamination Variations

• Variations in layering exist across different brain regions, some having fewer layers (3-4).

Neocortical Connectivity Patterns

• Thalamic input is a crucial pathway, delivering sensory information primarily to layer 4.
• Brainstem activity affects the whole cortex, influencing arousal and cognition.

Association Cortex

• Association cortex receives input from various thalamic nuclei (including pulvinar and medial dorsal nuclei).
• Primary sensory and motor cortices are relatively smaller parts, and receive sensory information via thalamic nuclei.

Parietal Association Cortex

• Involved in spatial attention and perceptual awareness.
• Damage can lead to visual neglect (ignoring one side of the visual field) and apraxia (difficulty with planned movements).
• The right parietal cortex is more dominant for spatial attention, influencing both visual fields. Language processing is more associated with the left parietal cortex.

Attentional Behavior

• Attention enhances activity in specific brain regions, particularly the contralateral visual cortex when processing visual stimuli and related extra striate visual cortices.
• Neurons involved in visual attention exhibit increased firing rates during task execution and with increasing reward.

Temporal Association Cortex

• Damage leads to agnosias (problems with object recognition).
• Recognition of faces, voices, and objects is related to specific areas within the inferior temporal lobe.
• Face recognition features brain activity in identified regions, but a scrambled face elicits less response.
• Gnostic neurons (e.g., "Jennifer Aniston cells") are uniquely responsive to specific complex stimuli like faces or concepts.

Frontal Association Cortex

• The frontal association cortex, located at the front of the brain, integrates complex information from sensory, motor, temporal, and association cortices, contributing to decision-making, planning, personality, working memory, and social behavior.
• Damage can lead to changes in personality, impairment in planning and social behavior, and difficulty with complex cognitive tasks.
• Frontal cortex activation during tasks are present.
• The dorsolateral prefrontal cortex plays a crucial role in tasks requiring planning and working memory. Delayed-response tasks can assess frontal lobe function.