Retrograde amnesia

In humans, the phenomenon of temporally graded retrograde amnesia has been described in the clinic and the laboratory for more than 100 years. In the 1990s, retrograde amnesia began to be studied prospectively in experimental animals. We identified 13 published studies in which animals were given eq uivalent training at two or more separate times before damage to the fornix or hippocampal formation. Eleven of these studies found temporally graded retrograde amnesia, with the extent of amnesia ranging from several days to a month or two. We consider these studies and also suggest why temporally graded retrograde amnesia has sometimes not been observed. Although the evi dence in favor of temporally graded retrograde amnesia is substantial, the inference from this work, that memory is reorganized as time passes, is rat her vague and depends on mechanisms yet to be identified. It is therefore e ncouraging that many opportunities exist for moving beyond purely descripti ve studies to studies that involve treatments or manipulations directed tow ard yielding information about mechanisms. Published 2001 Wiley-Liss, Inc.d agger