MEMORY PERFORMANCE FOLLOWING UNILATERAL ELECTRICAL-STIMULATION OF THE HIPPOCAMPUS IN A CHILD WITH RIGHT TEMPORAL-LOBE EPILEPSY

Verbal and visual memory performance was evaluated during unilateral stimulation of the hippocampus in an 11-year-old child with complex partial epilepsy associated with a right mesial temporal lobe focus. Memory was assessed during left and right hippocampal stimulation as well as preoperatively and 6-months postoperatively following anterior temporal lobe resection including removal of the anterior portion of the hippocampus. Stimulation of the left hippocampus resulted in a mild to moderate decrement in both verbal and visual memory performance as compared with a right hippocampal stimulation. In addition, stable or improved performance on memory assessment as well as general neuropsychological evaluation was noted 6 months postoperatively. Taken together, these data suggest that, in this child with early seizure onset (8 months of age), visual learning/memory functions shifted to the contralateral hippocampus and associated structures following damage to the right mesial temporal lobe structures. In addition, verbal learning/memory continues to be mediated by the left hippocampus, as expected. Thus, it appears that, as in the case of language lateralization, there may be a distinct subset of temporal lobe seizure patients (i.e., early seizure onset, high seizure frequency, chronic duration) in whom the brain has the capacity to shift material-specific memory functions to the contralateral mesial temporal lobe structures.