MEMORY IMPAIRMENT IN PATIENTS WITH STEREOTAXIC LESIONS TO THE HIPPOCAMPUS AND AMYGDALA

The study aimed at testing: (1) whether stereotaxic damage to the hipp ocampus and amygdala results ina memory deficit, (2) whether the memor y functions subserved by the hippocampus are lateralized and (3) wheth er time limited storage of sensory information is impaired after focal hippocampal and amygdalar lesions. Seven patients with unilateral ste reotaxic damage to the anterior part of hippocampus and unilateral or bilateral damage to the medial part of amygdala and 11 control subject s with no brain damage participated in the research. They were present ed with memory tests that required either remembering a spatial arrang ement of simultaneously presented verbal vs nonverbal stimuli or a tem poral order of sequentially presented items. Moreover, a sensory infor mation storage test was used. The results indicate that even small dam age limited to the anterior part of the hippocampus and medial part of the amygdala results in a mild memory deficit. Memory impairment was not related to the side of hippocampal lesion. This suggests that memo ry function subserved by the hippocampus is not lateralized. Different ial effects of left and right lobectomies found in previous studies we re, thus, probably due to the damage to temporal cortex. The results s howed, however, that sensory information storage limited to 3 s is not impaired after focal damage to the hippocampus and amygdala. A clear lateralization effect showing right hemisphere advantage in that funct ion was found.