Memory and the Medial Temporal Lobe

The next article in our series is a report published in 1957 by Scoville and Milner¹ describing the effects of bilateral medial temporal lobe resection on memory function. One of the subjects in the report, H. M., is considered the index case of amnesia resulting from temporal lobe injury.²

H. M. suffered with frequent generalized seizures that were not adequately controlled by anticonvulsant therapy. The surgery was a radical experiment that was felt to be justified by the patient's incapacitation and lack of response to available treatment. H. M.'s bilateral medial temporal lobe resection included the hippocampal formation and adjacent structures including most of the amygdaloid complex and entorhinal cortex.³

The effect of the surgery on his memory was dramatic and immediately evident. Formal neuropsychological testing demonstrated dense amnesia for all events following the surgery and intact memory for events that occurred prior to 19 months preceding surgery.

Scoville and Milner concluded that the hippocampus was crucial for the formation of memory to recent events, and they had the prudence to consider that adjacent structures such as the amygdala might also be involved. Amnesia from ischemic injury limited only to the hippocampus has also been found to impair acquisition of new memory, but not to the severe degree experienced by H. M.²