ANTEROGRADE AMNESIA
Certain lesions in the temporal cortex (specifically, in the hippocampus and nearby subcortical regions) produce a memory disorder called anterograde amnesia (anterograde means "in forward direction"). Patients with this disorder often have little trouble remembering events prior to the injury; their difficulty, instead, is in learning anything new. This kind of amnesia can occur as a result of various brain lesions. For example, it occurs in certain chronic alcoholics who suffer from Korsakoff's syndrome (named after the Russian physician who first described it). Anterograde amnesia is also one of the symptoms of Alzheimer's disease.
RETROGRADE AMNESIA
An opposite set of deficits occurs in retrograde amnesia (retrograde means "in a backward direction"), in which the patient suffers a loss of memory for some period prior to the brain injury. A brief period of retrograde amnesia always follows electroconvulsive therapy, a treatment for severe depression or mania that involves brief electric shocks applied to the head. Patients receiving this therapy have no memories of their treatments or the events directly preceding. Longer periods of retrograde amnesia, lasting weeks or even years, can result from brain tumors, diseases, or strokes.
