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For tests of autobiographical knowledge, it is often not possible to verify the accuracy of the recollections, and there are also difficult issues concerning how best to score the content of what is remembered. For tests of factual knowledge (e.g., public events tests), individuals vary widely in how much they know about the subject matter, independent of the influence of amnesia. In a few other cases of medial temporal lobe lesions, detailed neurohistological information is presented, but only clinical impressions are available about the RA ( Victor et al., 1961 Penfield and Mathieson, 1974 Victor and Agamanolis, 1990).Īnother major difficulty is that the study of past memory in amnesic patients relies necessarily on retrospective methods and imperfect tests. Neurohistological data from postmortem examination, in conjunction with quantitative neuropsychological data about RA, are available for only four patients with lesions restricted bilaterally to the medial temporal lobe. In some instances, useful anatomical information has been obtained from magnetic resonance imaging (MRI), although the amount of available detail varies greatly across studies.
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Yet anatomical data could be fundamental to understanding similarities and differences in the behavioral findings. A major factor is that, even when quantitative neuropsychological testing is performed, adequate neuropathological information about the patients is not always available. There are several reasons why these issues have been slow to resolve. Alternatively, RA has been described as affecting autobiographical memory across a patient’s entire lifetime and affecting fact memory to a much lesser degree ( Nadel and Moscovitch, 1997). With respect to what kind of memory impairment occurs, RA sometimes has been described as affecting both fact (semantic) memory and autobiographical (episodic) memory similarly ( Verfaellie et al., 1995 Rempel-Clower et al., 1996). Alternatively, RA has been described as usually temporally graded, sparing remote memory ( Marslen-Wilson and Teuber, 1975 Squire and Alvarez, 1995). For example, RA has been described as typically extensive and ungraded, affecting recent and very remote memories alike ( Sanders and Warrington, 1971 Warrington, 1996). Yet the facts themselves are not agreed on. An understanding of RA should have considerable implications for understanding the organization of normal memory as well as the function of the damaged brain structures. The condition is commonly observed after medial temporal lobe or diencephalic pathology, and it has fascinated psychologists, biologists, and clinicians for over 100 years ( Ribot, 1881). Retrograde amnesia (RA) refers to loss of memory for information acquired before the onset of amnesia.
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The results suggest that whether retrograde amnesia is temporally limited or very extensive depends on whether the damage is restricted to the hippocampal formation or also involves additional temporal cortex. The two patients with more extensive temporal lobe damage had severe anterograde amnesia and extensive retrograde memory loss for both facts and events. Content analysis could not distinguish the autobiographical recollections of the patients from the recollections of control subjects. The two patients with hippocampal formation lesions had moderately severe anterograde amnesia and limited retrograde amnesia for facts and events that affected, at most, the decade preceding the onset of amnesia. Two patients with presumed hippocampal formation lesions and two patients with more extensive temporal lobe damage, all of whom became amnesic in a known year, were given tests of anterograde and retrograde memory function.