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

- Verbal recall memory is impaired by dominant MTL stimulation.
- Stimulation during the interval between learning and recall most strongly disrupts recall.
- MTL stimulation does not alter arithmetic performance, demonstrating cognitive specificity of this effect.
- The well-known tendency to begin recall of short lists with the first word diminishes with MTL stimulation.
- Either enhanced contextual flushing or disruption of replay are the likely cognitive mechanisms explaining our results.

BackgroundDirect 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.ObjectiveTo study the effects of MTL stimulation on memory performance.MethodsWe 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).ResultsWe 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.ConclusionsThe results suggest that recall is most dependent on the MTL between learning and retrieval.