Journal of Neuroscience, Vol 9, 828-839, Copyright © 1989 by Society for Neuroscience
The neurology of memory: quantitative assessment of retrograde amnesia in two groups of amnesic patients
LR Squire, F Haist and AP Shimamura
Veterans Administration Medical Center, University of California, San Diego, La Jolla 92093.
The phenomenon of retrograde amnesia has important implications for
understanding normal memory as well as its neural organization. Using 6
tests of remote memory, we evaluated the extent and severity of retrograde
amnesia in 2 groups of amnesic patients--7 patients with alcoholic
Korsakoff's syndrome and 5 other patients with amnesia (anoxia or ischemia,
N = 3; thalamic infarction, N = 1; unknown etiology, N = 1). Although there
were individual differences, Experiment 1 showed that the severity and
extent of retrograde amnesia was similar for the 2 groups. Retrograde
amnesia was temporally graded across a period of about 15 years and was not
detectable in more remote time periods. In Experiment 2, repeated testing
during a 3 year period showed that amnesic patients and control subjects
were similarly consistent in their responses. Amnesic patients did not
catch up to control subjects by eventually accumulating as many correct
answers as the control subjects. In Experiment 3, amnesic patients
performed normally on a test of very difficult general information
questions, which were based on material likely to have been learned long
ago. In all 3 experiments, the 2 groups of amnesic patients performed
similarly. The results support the following conclusions: (1) Extensive,
temporally graded retrograde amnesia, which has been observed frequently in
patients with Korsakoff's syndrome, occurs readily in other amnesic
patients as well, even when their memory impairment appears well
circumscribed; (2) patients with presumed damage to either the medial
temporal or the diencephalic brain structures linked to memory functions
can produce a similar kind of retrograde amnesia; (3) the impairment
reflects a loss of usable knowledge, not simply difficulty accessing an
intact memory store that can then be overcome given sufficient retrieval
opportunities; (4) very remote memory, at least for factual information,
can be intact in amnesia; (5) the structures damaged in amnesia support
memory storage, retrieval, or both during a lengthy period of
reorganization, after which representations in memory can become
independent of these structures.
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