Retrograde amnesia and consolidation: anatomical and lesion considerations.

The four papers in this issue of Hippocampus dealing with retrograde amnesia, together with relevant animal studies in the literature, are reviewed from the perspective of the anatomical location of the lesion and extent of damage to the brain. In order to evaluate the underlying damage in these and related prospective experimental studies, it is necessary to consider both the lesion techniques that were used as well as the care with which the resulting damage was determined. Both temporally graded and flat, ungraded retrograde amnesia have been reported, as well a lack of effects, following damage to structures in the medial temporal area. Most research has centered around damage to the hippocampus, but differences in selectivity of the lesions and behavioral testing procedures preclude any definite conclusions regarding the precise nature of the involvement of this structure. With a greater appreciation for the importance of the locus and extent of the damage, together with the kind of information being processed, it should be possible to obtain a better understanding of the neural substrates underlying retrograde amnesia.