Remembering and forgetting of semantic knowledge in amnesia: a 16-year follow-up investigation of RFR

Abstract

We report our long-term follow-up investigations of RFR, a post-encephalitic case of very grave anterograde and retrograde amnesia. We also describe the results of quantitative neuroimaging of his brain injury that showed bilateral and severe reduction in the hippocampal formation and medial temporal structures with sparing of left lateral/posterior and right posterior temporal cortex. We established that RFR had a persistent severe anterograde and retrograde amnesia for personal and public events. His personal semantic knowledge was relatively spared for the retrograde period. There was a modest and global reduction in RFR's vocabulary for words acquired in adulthood before he became amnesic but there was no evidence of any retrograde gradient. His retrograde knowledge of people was also without any gradient. Remarkably, there had been no change in the extent of his semantic knowledge across a prolonged re-test interval indicating that the loss of semantic knowledge was stable and likely to have arisen at the time of his initial lesion. RFR also showed evidence of a limited but significant ability to acquire new word meanings and a more restricted capacity for learning about new celebrities. While he was able to demonstrate face and name familiarity for newly famous people, he was unable to provide much semantic detail. RFR's amnesia can be partially explained by contemporary theories that allow for parallel cortical and hippocampal memory systems but is difficult to reconcile in detail with any extant view.