seizure /sē″zhər/ [Fr, saisir, to seize] , a hyperexcitation of neurons in the brain leading to abnormal electric activity that causes a sudden, violent involuntary series of contractions of a group of muscles. It may be paroxysmal and episodic, as in a seizure disorder, or transient and acute, as after a head concussion. A seizure may be clonic or tonic; focal, unilateral, or bilateral; or generalized or partial. Also called convulsion.
