CerebralCortex

The cerebral cortex is a 2-4mm thick sheet of neuronal cell bodies (gray matter) forming the outermost layer of the cerebrum, folded into gyri and sulci to maximize surface area. Histologically, it is organized into six layers (neocortex) with varying neuronal types and connections, classified by Brodmann areas based on cytoarchitecture. Functionally, the cortex is divided into: primary motor cortex (precentral gyrus, Brodmann area 4) controlling contralateral voluntary movement with somatotopic organization (homunculus); primary somatosensory cortex (postcentral gyrus, areas 3,1,2) processing contralateral sensory input; primary visual cortex (occipital lobe, area 17) receiving retinotopic visual input; primary auditory cortex (superior temporal gyrus, areas 41,42); and association areas integrating information for higher cognition. Language areas include Broca's area (inferior frontal gyrus, areas 44/45) for speech production and Wernicke's area (superior temporal gyrus, area 22) for language comprehension, typically lateralized to the dominant (usually left) hemisphere. The prefrontal cortex governs executive function, personality, and judgment—damage causes disinhibition or apathy (as in frontal lobe syndromes). Parietal lobe lesions (especially non-dominant) cause hemispatial neglect, apraxia, or Gerstmann syndrome (agraphia, acalculia, finger agnosia, left-right confusion) with dominant hemisphere angular gyrus lesions. Temporal lobe involvement relates to memory (hippocampus), auditory processing, and in cases of medial temporal lesions, amnesia. Clinically, understanding cortical localization is crucial for diagnosing stroke syndromes (e.g., MCA vs ACA territory infarcts), seizure semiology (localizing epileptogenic foci), and neurodegenerative patterns (e.g., frontotemporal dementia vs Alzheimer's, which preferentially affects hippocampus/temporal-parietal association cortex). The cortex also demonstrates plasticity, important in stroke recovery and rehabilitation. Vascular supply follows the anterior, middle, and posterior cerebral arteries, correlating with specific functional deficits when occluded—a cornerstone of stroke localization on board exams.