Study Notes: Cognitive Functions and Association Cortices

Cognition is the mental process of acquiring knowledge via thought, experience, and sensory input, facilitated by the association cortices.
The neocortex consists of six distinct cellular layers with specific connectivity profiles.
$\text{Layer } 5$ primarily projects to the thalamus and subcortical structures.
Brodman systematically documented these differences in cytoarchitecture, identifying specific regions such as $Area\,17$ (primary visual cortex).
Inputs to the association cortices include processed information from the thalamus, cortico-cortical connections (both ipsilateral and interhemispheric), and the brainstem (modulating alertness).

The parietal lobe represents the three-dimensional layout of the world and manages spatial attention.
Right parietal lobe damage typically leads to visual neglect, where a patient ignores the left side of space or objects despite intact low-level vision ( $V1$ and $V2$ ).
Bilateral damage results in Balan syndrome, consisting of three symptoms: simulatine dossier (seeing only one object at a time), optic ataxia (impaired reaching/grasping), and ocular apraxia (difficulty directing eye movements).
Attending to stimuli enhances neural firing rates in sensory regions, as demonstrated by macaque electrophysiology and human fMRI studies.

The temporal lobe is central to the "what" pathway, responsible for identifying and naming stimuli.
Damage to this region causes agnosia; prosopagnosia is a specific inability to recognize familiar faces, often linked to the fusiform gyrus.
Specialized neurons in the inferior temporal cortex exhibit selective responses to specific objects or face profiles.
Human intracranial recordings identified neurons that respond to specific individuals (e.g., Jennifer Aniston cells), though most visual representation likely involves population coding.

The frontal lobe is the largest lobe, maturing into the mid- $20s$ , and integrates high-level information to guide behavior.
Executive functions include impulse control, personality, future planning, and social restraint.
Phineas Gage and Joe A. are classic cases illustrating how frontal damage causes dramatic personality changes and loss of planning ability despite normal intelligence.
The dorsolateral prefrontal cortex manages response inhibition and working memory, while the ventromedial prefrontal cortex facilitates adaptive, reward-based decision-making.
Frontal neurons remain active during the delay period of tasks, suggesting they hold information for future action rather than executing the action itself.

Synesthesia involves involuntary, consistent cross-modal experiences (e.g., grapheme-color synesthesia).
It has a prevalence of $1\%$ to $4\%$ and demonstrates a genetic link within biological relatives.
Research using the Stroop effect confirms its involuntary nature by showing that incongruent colors (e.g., the letter A appearing in a different color than the synesthetic color) cause measurable interference in response times.

Distinguishing Neglect from Hemianopia: Vision loss (hemianopia) results in awareness of a blind spot, leading to compensatory head movements. In contrast, neglect involves anosognosia, where patients are unaware they are failing to attend to half of their environment.
Face Recognition Deficits: To confirm a specific face-recognition deficit, researchers must rule out deficits in low-level vision, general memory, attention, and general object recognition.
Parietal Asymmetry: The right parietal lobe controls attention for both sides of space, whereas the left parietal lobe primarily controls attention for the right hemifield ( $contralateral$ ).