Hippocampal involvement in spatial and working memory: A structural MRI analysis of patients with unilateral mesial temporal lobe sclerosis

Forty-seven patients with unilateral temporal lobe epilepsy (TLE) were inve stigated on the Nine-Box Maze. The task was designed to compare working mem ory and spatial mapping theories of the functions of the hippocampus and pr ovide measures of spatial, object, working, and reference memory. The resul ts extended our previous findings in a larger group of patients. Spatial me mory deficits across both working and reference memory conditions were foun d in patients with a right epileptogenic focus. There was no evidence of an object working memory deficit, but a nonlateralized impairment in object r eference memory was revealed, which is consistent with our previous finding s. The pattern of results was confirmed in a subgroup of 33 patients with u nilateral atrophy localized to the hippocampus and parahippocampal gyrus, a s verified by volumetric analysis of magnetic resonance images. In addition spatial memory errors significantly correlated with volumetric measures of mesial temporal lobe structures and not with measures of the remaining tem poral cortex. In contrast, object reference memory errors correlated with v olumetric measures of the temporal cortex and not with mesial temporal lobe structures. These findings support a specialized role for the right hippoc ampal region in spatial memory (C) 1999 Academic Press.