Medial temporal lobe structures are needed to re-experience remote autobiographical memories: evidence from H.M. and W.R.

The nature and extent of retrograde amnesia in patients with medial temporal lobe (MTL) lesions is currently under debate. While some investigators propose a temporally limited role for the MTL in episodic and semantic memory, others claim that MTL structures are needed for episodic memories of one's entire lifetime, and that only semantic memory becomes independent of the MTL. To address this issue, we tested two amnesic patients, H.M. and W.R., with bilateral MTL lesions on a series of remote memory tests that together distinguished episodic memory from semantic memory performance. Notably, we used a new method to assess autobiographical memory that measured the degree of re-experiencing of personal happenings from the past. Both patients showed relatively spared semantic memory, but severe impairment on measures of autobiographical memory, with no temporal gradient. Our data support the view that MTL structures play a significant role in recalling specific personal episodes, not only from the recent past but from the distant past as well.