SELECTIVE SPATIAL MEMORY IMPAIRMENT AFTER RIGHT UNILATERAL TEMPORAL LOBECTOMY

Deficits in performance of both spatial and visual tasks are common fo llowing tissue loss in the right temporal lobe. Since spatial and visu al attributes are frequently confounded in experimental tasks, we have studied patients following unilateral temporal lobectomy, in an attem pt to determine which aspect mediates the observed deficits. Spatial a nd visual memory performance was compared in normal controls (n = 16), left temporal (LTL; n = 19) and right temporal (RTL; n = 19) lobectom y patients, by presentation of eight abstract designs in a spatial arr ay for subsequent recall and recognition of the designs (visual memory ) and recall of their spatial position (spatial memory). By varying th e retention intervals for each group, all three groups were matched on both recall and recognition of the designs at sub-ceiling levels. In contrast, recall of the position of the designs (spatial memory), test ed at equivalent delays to those of the visual memory tests, revealed a deficit in the RTL patients compared to both controls and LTL patien ts (p < 0.05). Magnetic resonance imaging (MRI) was used to quantify t he extent of resection of the hippocampus and parahippocampal regions in the two patient groups and showed a significant correlation between hippocampal and parahippocampal removal and spatial memory in the RTL group only. These data support the notion of a disproportionately lar ge involvement of the right hippocampus and adjacent regions in spatia l memory. (C) 1998 Elsevier Science Ltd. All rights reserved.