Stimulation of the human medial temporal lobe between learning and recall selectively enhances forgetting.

BACKGROUND Direct electrical stimulation applied to the human medial temporal lobe (MTL) typically disrupts performance on memory tasks, however, the mechanism underlying this effect is not known. OBJECTIVE To study the effects of MTL stimulation on memory performance. METHODS We studied the effects of MTL stimulation on memory in five patients undergoing invasive electrocorticographic monitoring during various phases of a memory task (encoding, distractor, recall). RESULTS We found that MTL stimulation disrupted memory performance in a timing-dependent manner; we observed greater forgetting when applying stimulation during the delay between encoding and recall, compared to when it was applied during encoding or recall. CONCLUSIONS The results suggest that recall is most dependent on the MTL between learning and retrieval.