Retrograde amnesia in patients with hippocampal, medial temporal, temporal lobe, or frontal pathology

There is considerable controversy concerning the theoretical basis of retrograde amnesia (R.A.). In the present paper, we compare medial temporal, medial plus lateral temporal, and frontal lesion patients on a new autobiographical memory task and measures of the more semantic aspects of memory (famous faces and news events). Only those patients with damage extending beyond the medial temporal cortex into the lateral temporal regions showed severe impairment on free recall remote memory tasks, and this held for both the autobiographical and the more semantic memory tests. However, on t-test analysis, the medial temporal group was impaired in retrieving recent autobiographical memories. Within the medial temporal group, those patients who had combined hippocampal and parahippocampal atrophy (H + ) on quantified MRI performed somewhat worse on the semantic tasks than those with atrophy confined to the hippocampi (H � ), but scores were very similar on autobiographical episodic recall. Correlational analyses with regional MRI volumes showed that lateral temporal volume was correlated significantly with performance on all three retrograde amnesia tests. The findings are discussed in terms of consolidation, reconsolidation, and multiple trace theory: We suggest that a widely distributed network of regions underlies the retrieval of past memories, and that the extent of lateral temporal damage appears to be critical to the emergence of a severe remote memory impairment. The neural bases of retrograde amnesia and long-term memory functions remain key issues in cognitive neuroscience. In particular, the time course of medial temporal lobe (MTL) involvement in the storage and retrieval of remote memories has not been resolved. The present study examines performance across a range of measures of remote memory in amnesic patients with focal medial temporal lobe pathology, more widespread temporal lobe damage, and frontal lobe damage. The purpose is to test theoretical predictions concerning the nature of retrograde amnesia. Despite a proliferation of studies on memory and its disorders over the last three to four decades, many of the critical issues are still widely debated (Kopelman 2002, 2006). There are two main theoretical positions currently discussed in the literature regarding the role of MTL structures in the retrieval of remote memories, each of which makes distinct predictions about how remote memory is affected by the physical location and extent of brain damage. According to the consolidation model (ZolaMorgan and Squire 1990; Squire 1992; Squire and Alvarez 1995), episodic (autobiographical events) and semantic memories are processed in the same way, initially dependent on the hippocampal formation, but over time they become represented in the neocortex, independently of medial temporal structures. In contrast, multiple trace theory (Nadel and Moscovitch 1997, 2001;