frontal lobe

The frontal lobe is divided into several functional regions: the primary motor cortex (precentral gyrus) controls contralateral voluntary movement organized somatotopically per the motor homunculus; the premotor and supplementary motor areas plan and coordinate movement; the prefrontal cortex is responsible for executive functions including judgment, planning, impulse control, working memory, and personality; and Broca's area (typically left inferior frontal gyrus, pars triangularis/opercularis) is responsible for speech production—damage causes non-fluent (expressive) Broca aphasia with intact comprehension but effortful, telegraphic speech. The frontal eye fields control voluntary conjugate gaze (lesions cause eyes to deviate toward the lesion side, away from hemiparesis). Frontal lobe lesions can result from trauma, stroke (especially ACA territory affecting medial frontal lobe causing contralateral leg weakness and urinary incontinence), tumors (e.g., meningioma), or neurodegenerative disease (frontotemporal dementia, notably behavioral variant with Pick bodies histologically). Clinical hallmarks of frontal lobe dysfunction include disinhibition, apathy, poor judgment, personality change, primitive reflexes (grasp, suck, palmomental), urinary incontinence, and gait apraxia. The classic case of Phineas Gage illustrates dramatic personality change after prefrontal damage. Frontal lobe seizures can cause bizarre motor behaviors, often nocturnal, and may be misdiagnosed as psychiatric events. Testing frontal lobe function includes Luria test (fist-edge-palm), go/no-go tasks, and assessing abstraction (proverb interpretation) and set-shifting (Wisconsin Card Sorting Test).