Lateralization of verbal memory and unilateral hippocampal sclerosis: evidence of task-specific effects

This study retrospectively investigated the effect of left (LHS) versus right (RHS) hippocampal sclerosis on verbal memory, measured by means of the Paired Associate Learning and Logical Memory subtests of the Wechsler Memory Scale (WMS) administered as part of a routine preoperative assessment. Patients were selected for the presence of unilateral hippocampal sclerosis by means of preoperative magnetic resonance imaging (MRI) and postoperative neuropathology. The LHS patients (n = 20) were significantly worse on paired associate learning than RHS patients (n = 18), the performance of RHS patients being consistent with normative standards. In contrast, no laterality effect was seen on the immediate and delayed recall of passages; the evidence suggests that both groups performed at a mildly impaired level. It was suggested that the laterality of verbal memory is conditional upon specific task demands in patients with damage to mesial temporal structures.