Temporal memory in human amnesic subjects and rats with specific brain lesions

Abstract

Temporal processing was assessed in a group of alcoholic Korsakoff subjects, post viral encephalitic subjects, alcoholic control and normal control subjects. Subjects were tested on their ability to reproduce and estimate intervals of time ranging from 3 to 96 seconds. Also, a computerised analogue of the fixed interval procedure used with animals was designed and used to test subjects' estimations of intervals of 15 and 30 seconds. Memory for temporal order was also assessed using an object recency task which also incorporated a recognition memory test. It was found that Korsakoff subjects were impaired at all intervals both in the temporal estimation tests and the fixed interval procedure compared to the alcoholic control subjects, whereas the post-encephalitic subjects performed similarly to the normal control group. Both amnesic groups, however, were severely impaired on the test of temporal order memory. The results suggested that these two aspects of temporal processing were unrelated and that neither was related to severity of amnesia. There was no evidence to support the view that amnesic subjects' temporal order deficits are a result of frontal lobe dysfunction, but the temporal duration judgments correlated significantly with tests of cognitive estimation suggesting a contribution of frontal lobe function to estimation of temporal duration. Temporal order memory was assessed in rats with either radiofrequency lesions of the fornix or aspiration lesions of medial prefrontal cortex using a delayed non-matching to sample procedure. Neither lesion group was impaired on this test of recency memory although both were impaired on a spatial non-matching task. These results are discussed in relation to previous animal studies and their implications for human amnesia.