In Newsdesk (August, 2005),1 new evidence for the neuroanatomy of remote memory was reported. On the basis of the findings of the US team lead by Larry Squire,2 remote autobiographical memory was suggested to be independent of the medial temporal lobe but dependent on the neocortex. By contrast with previous hypotheses, this new proposal predicts that after damage to the medial temporal lobe only recent autobiographical memories should be impaired in neurological patients, whereas loss of both recent and old autobiographical memories implies additional damage in the neocortex. However, there is evidence not included in the Newsdesk article, that is problematic for this new prediction.Two patients, NT and VC, were previously reported to have lesions restricted to the medial temporal lobe and exhibited loss of remote memories extending for decades. Patient NT presented with extensive and ungraded retrograde amnesia after a right temporal lobectomy.3 This patient had substantial difficulty recalling autobiographical memories dating to childhood. The neuropathological investigations revealed clear-cut sclerosis of the unresected left hippocampus, but all other cortical areas, including the previously removed right temporal lobe, were normal. Thus, it is tempting to conclude that her severe remote memory loss was a consequence of her bilateral hippocampus damage.Detailed cognitive testing of the severely amnesic patient VC reinforces this conclusion.  and  On all retrograde memory tests, including the standard autobiographical memory interview, his results were equally poor over all periods tested: he had no autobiographical recollection from any period of his life. Qualitative MRI, MRI volumetry, voxel based morphometry, spectroscopy, and functional MRI showed that the primary abnormality was located in the hippocampus bilaterally. Only MRI volumetry identified a slight decrease of the left parahippocampal volume, but functional neuroimaging showed that this region was active in VC during memory retrieval. Therefore, investigations of VC suggest that the hippocampus is crucial for remembering one's personal past. This finding is consistent with those from other lesion and neuroimaging studies.6The discrepancy in findings between patients such as NT and VC and those reported by Squire's team may depend on important differences in the patients' severity of amnesia. For example, Bayley and colleagues2 draw attention to the test results of patients (EP and GP) with selective damage to the temporal medial lobe who obtained maximum scores on the childhood portion of the autobiographical memory interview (9/9), by contrast with the very impaired score of VC (1/9). However, EP and GP's performance on other standard memory tests was only mildly impaired, whereas on similar tests VC barely could score any points.We suggest, therefore, that questions regarding the neuroanatomy of remote memory, and particularly the role of the medial lobe and hippocampus, are far from resolved. Further studies of amnesic patients with well-documented and restricted lesions are needed to ascertain the critical anatomical structures affected in remote memory.
|Numero di pagine||2|
|Stato di pubblicazione||Published - 2005|
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