Lost for words or loss of memories? Autobiographical memory in semantic dementia

摘要

Recent reports have suggested that patients with semantic dementia show a loss of early (remote) auto-biographical memories with pronounced sparing of recent memories (Graham Hodges, 1997; Snowden, Griffiths, & Neary, 1996), i.e., a "reversed" temporal gradient or "Ribot effect". At first sight, these findings suggest that the deficits in "semantic" dementia go beyond the semantic domain, involving aspects of autobiographical (episodic) memory. It has also been proposed that there is a "step-like" function with personal memories preserved for 18 months to 2 years in the immediate past. This view is consistent with the theory that the hippocampal complex/medial temporal lobe (relatively intact in semantic dementia) plays a time-limited role in the acquisition and storage of memories, while the temporal neocortex (damaged in semantic dementia) is required for long-term storage and retrieval. In this study we ask whether (a) previous tests have underestimated the integrity of remote memory in semantic dementia as a result of not allowing for these patients' comprehension and language production difficulties, and (b) whether a recency effect, if obtained, is genuinely step-like or more graded. We used a cued autobiographical memory interview with semantic dementia patient, IH, to examine the effect of providing increasingly specific lexical cues to probe salient events throughout his lifespan. Results demonstrated that the provision of specific cues enabled IH to access and express memories from his childhood and early adulthood as well as from more recent times. There was a gentle recency effect only for intermediate levels of cueing, indicating that recent memories were easier to retrieve and/or express in the absence of specific cues, but this effect was graded, with no evidence of a step-like cut-off at 18 months or 2 years before testing. In brief, our findings are consistent with the view that the deficits in semantic dementia are predominantly or exclusively semantic, rather than involving the storage of autobiographical memories per se.