![]() Specifically, we looked for regions that exhibited gradually decreasing activity as participants recalled memories from 1–12 years ago and a constant level of activity during recall of more remote memories (from 13–30 years ago). We used the same test materials (News Events Test) that had revealed temporally limited retrograde amnesia in memory-impaired patients with hippocampal lesions ( Manns et al., 2003 Bayley et al., 2006), and we looked for brain regions in which activity during recall of 1- to 30-year-old memories conformed to the function suggested by the findings from patients. ![]() Guided by the findings from patients, we have assessed brain activity while participants recalled semantic memories from seven different time periods covering the past 30 years. Yet other studies found no difference in the activity in these structures during recollection of recent and remote semantic memories ( Maguire et al., 2001 Maguire and Frith, 2003 Bernard et al., 2004). Some studies, in keeping with the findings from memory-impaired patients, found more activity in hippocampus or entorhinal cortex during recollection of recent semantic memories than during the recollection of remote semantic memories ( Haist et al., 2001 Douville et al., 2005 Takashima et al., 2006). ![]() ![]() For example, in a semantic memory test involving news events that occurred 1–30 years before the onset of amnesia, memory for remote events was intact (11–30 years before amnesia), but memory for events that occurred recently was impaired in a graded manner (1–10 years before amnesia) ( Manns et al., 2003 Bayley et al., 2006).Ī number of brain imaging studies have also investigated how recent and remote semantic memory are represented in the healthy brain, but findings from these studies are mixed. Memory-impaired patients with circumscribed, bilateral lesions of the hippocampus exhibit both impaired new learning (anterograde amnesia) and temporally graded retrograde amnesia covering a period of a few years before the onset of memory impairment ( Kapur and Brooks, 1999 Manns et al., 2003). Subsequently, it became possible to relate these observations to neuroanatomy and especially to the functions of the hippocampus. The results support the idea that medial temporal lobe structures play a time-limited role in semantic memory.Įarly descriptions of memory impairment emphasized that the recent past is typically more vulnerable to disruption than the remote past ( Ribot, 1881 Russell and Nathan, 1946). Last, activity in a different group of regions (perirhinal cortex, parahippocampal cortex, and inferior temporal gyrus) was associated with how well the test questions were subsequently remembered. The findings for all of these regions were unrelated to the richness of the memories, to how well test questions were remembered later (encoding for subsequent memory), nor to how frequently semantic memories were accompanied by personal, episodic recollections. Regions in the frontal lobe, temporal lobe, and parietal lobe exhibited the opposite pattern. Regions in the medial temporal lobe exhibited a decrease in brain activity in relation to the age of the memory (hippocampus, temporopolar cortex, and amygdala). Guided by earlier findings from patients with damage limited to the hippocampus who were given the same test material, we looked for regions that exhibited gradually decreasing activity as participants recalled memories from 1–12 years ago and a constant level of activity during recall of more remote memories. We measured brain activity using event-related fMRI as participants recalled answers to 160 questions about news events that had occurred during the past 30 years.
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