Neuropsychology of remote and recent autobiographical memory

The central question addressed by the present work concerned the roles of the hippocampus and related medial temporal lobe (MTL) structures during retrieval of remote and recent autobiographical memories. Consolidation theories suggest that all memories become independent of the MTL as they age, while Multiple Trace Theory (MTT) proposes that this is true only of semantic memories, and that episodic memories remain MTL-dependent for as long as they exist. Neuroimaging of healthy persons revealed hippocampal activations during retrieval of remote and recent memories and that the extent of activation is dependent on the extent of subjective re-experiencing. Additionally, remote memories were associated with more distributed activations along the rostrocaudal axis of the hippocampus, which may be related to the observation that partial damage of the hippocampus causes greater loss of recent memories.;Converging evidence for the role of MTL structures in retrieval of remote episodic memories was obtained through neuroimaging of patients with unilateral temporal excisions due to temporal lobe epilepsy (TLE). The extent of retrograde memory loss in these patients was associated with the extent of excision and with activation of the remaining MTL tissue. Patients with intact remote autobiographical memory activated their remaining MTL tissue to the same extent as normal controls, whereas patients who were unable to recall context-rich personal memories showed no MTL activation or activations limited to the parahippocampal cortex. Finally, behavioural studies of patients with MTL lesions demonstrated dissociations between semantic/generic and episodic autobiographical memory. Patients with lesions restricted to the MTL were able to retrieve personal semantic/generic details from the past but showed severe deficits in retrieval of episodic details. This was true of free recall, cued recall and detail-recognition. When extensive loss of other MTL structures was present, recognition of generic and semantic personal details was also affected. Collectively, the present series of experiments supports the assertion that the hippocampal complex is involved in retrieval of context-rich memories for as long as they exist, as proposed by MTT. It also provides insight into the possible roles of extra-hippocampal structures within and outside of the MTL in supporting generic vs. episodic remote memories.