MESIAL TEMPORAL SPIKES INTERFERE WITH WORKING-MEMORY

The hippocampus and other mesial temporal structures support long-term memory and also are common foci for epilepsy. Recently it was shown t hat these brain structures may subserve the short-term storage and reh earsal processes called working memory in humans. We determined the ac curacy of verbal and visuospatial working memory in the presence and i n the absence of mesial temporal spikes in eight patients who had bila teral depth electrodes implanted to evaluate intractable epilepsy. Six of eight patients had declines in working memory performance during m esial temporal spiking, with the greatest disruption in spatial and ve rbal recall coincident with left hippocampal spikes (p = 0.019). Overa ll accuracy of working memory far all patients declined an average of 6% on spike trials. The two patients who did not have decreased accura cy during spike trials also had the best overall working memory perfor mance. Mesial temporal spikes were not detected on extracranial record ings and yet may be associated with declines in working memory in some patients with epilepsy.