What are functional areas?

Broca's aphasia (expressive/non-fluent): the patient struggles to produce speech, often speaking in short telegraphic utterances and omitting function words ('agrammatic' speech), but comprehension of simple sentences is relatively preserved. The person knows what they want to say but cannot produce it fluently. Caused by damage to the left inferior frontal gyrus (Broca's area). Wernicke's aphasia (receptive/fluent): the patient speaks fluently and at normal rate but uses incorrect words (paraphasias), neologisms, or word salad. Comprehension is severely impaired — the person often seems unaware they are making errors. Caused by damage to the left posterior superior temporal gyrus (Wernicke's area). Conduction aphasia: preserved fluency and comprehension but severely impaired repetition. Caused by damage to the arcuate fasciculus connecting the two areas. This dissociation confirmed the white matter connection between the two language areas.

Cortical maps are not fixed — they reorganise in response to experience, skill learning, and injury. This is cortical plasticity. In musicians, the cortical representation of the fingers used to play instruments is enlarged. In blind individuals, the visual cortex is recruited for processing tactile (Braille) and auditory information. After amputation, the cortical representation of the missing limb can be 'invaded' by adjacent body representations — a substrate for phantom limb pain. Although plasticity declines after early 'critical periods', the adult brain retains significant capacity for reorganisation, particularly following injury. Stroke rehabilitation exploits this — constraint-induced movement therapy forces use of the affected limb and drives cortical reorganisation that improves function.