1/7/2024 0 Comments Example of social amnesia![]() One implication of this finding for studies of retrograde amnesia is that combined hippocampus and subiculum lesions may be more disruptive than lesions limited to the hippocampus itself. Interestingly, studies of anterograde amnesia for the same task suggest that, to impair memory function, hippocampal lesions must be combined with lesions of the subiculum ( Alvarez et al., 2001). In both of these cases, the retrograde amnesia covered a period of ∼1–5 d. In studies of retrograde amnesia for a socially acquired food preference, TGRA was observed after lesions of the dorsal hippocampus ( Winocur, 1990) and also after larger lesions that damaged virtually all of the dorsal and ventral hippocampus but spared the subiculum ( Winocur et al., 2001). Subsequently, when the subject rat is presented with a choice between two odorous foods, the subject rat expresses a memory for this association by choosing the same food odor that was present on the demonstrator's breath. During this social interaction, the subject rat makes an association between the food odor and constituents of the demonstrator's breath ( Galef and Wigmore, 1983). This task involves a “demonstrator” rat that is fed an odorous food and is then allowed to interact with a “subject” rat. These ideas have been explored in rats using a learning paradigm based on the social transmission of a food preference. This idea predicts that TGRA will not be observed when hippocampal lesions are complete (e.g., recent and remote memories will be similarly impaired). ![]() TGRA occurs because a partial lesion of the hippocampus is more likely to spare a remote memory than a memory acquired recently ( Nadel and Moscovitch, 1997). In this view, older memories have a more redundant and spatially distributed representation within the hippocampus than recent memories. Over time and through a process of reorganization, the connections among the cortical regions are progressively strengthened until the cortical memory can be reactivated and retrieved independently of the hippocampus ( Squire and Alvarez, 1995).Īn alternative suggestion is that memories that are initially hippocampus dependent remain dependent on the hippocampus. Initially, the hippocampus serves to bind these cortical regions and to allow memory to be reactivated for retrieval. One account of the phenomenon suggests that memory is stored in the same neocortical structures that were involved in processing the relevant information during learning. This pattern of findings suggests that the hippocampus (and related structures) is necessary for memory storage and retrieval for only a limited time after learning. That is, animals with hippocampal damage, entorhinal damage, or fornix section typically have impaired memory for material learned just before surgery, but material learned more remotely is spared (for exceptions, see Sutherland et al., 2001). Temporally graded retrograde amnesia is the most common finding. Studies in experimental animals have the advantage that retrograde amnesia can be studied prospectively, the locus and extent of brain lesions can be determined accurately, and the timing and strength of original learning can be precisely controlled.Ī number of studies have been reported in which animals have been given equivalent amounts of training at two or more different times before damage to the hippocampal formation or the fornix ( Ramos, 1998 Squire et al., 2001). Studies of human amnesia have illuminated this phenomenon ( Hodges, 1994 Squire and Alvarez, 1995), but such studies necessarily rely on retrospective methods and imperfect tests. Temporally graded retrograde amnesia (TGRA) refers to a phenomenon of premorbid memory loss whereby information acquired recently is more impaired than information acquired more remotely. The results show the importance of the hippocampus and related structures for nonspatial memory and also demonstrate the temporary role of these structures in long-term memory. ![]() Hippocampal lesions that included the subiculum produced marked anterograde amnesia and a 1–30 d temporally graded retrograde amnesia. Normal rats exhibited memory of the acquired food preference for at least 3 months after learning. In experiment 3, large lesions of the hippocampus that included the subiculum were made 1, 10, or 30 d after learning to determine the nature and extent of retrograde amnesia. In experiment 2, we determined the anterograde amnesic effects of large lesions of the hippocampus that included the subiculum. Experiment 1 asked how long an acquired food preference could be remembered. We studied the importance of the hippocampus and subiculum for anterograde and retrograde memory in the rat using social transmission of food preference, a nonspatial memory task.
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