Dense Retrograde Amnesia, Intact Learning Capability and Abnormal Forgetting Rate: A Consolidation Deficit?

Following a thoracic trauma, which caused brain hypoxia, a 24-year-old man presented with a dense retrograde amnesia for events, persons and environments that spanned his whole life before injury. Knowledge acquired at school or through the media were equally lost, with the exception of arithmetical skills and some geographical knowledge. No deficit was apparent in language, object recognition, motor skills and intellectual tests. Anterograde memory was marked by very efficient learning capacity, an almost perfect retention of information at delay interval of 4 hours and pathologically rapid forgetting at longer delays. Informal observations agreed with test performance in showing that he could relearn facts of the past and easily acquire new information, but tended to lose these memories if the information was not frequently rehearsed. PET showed a hypometabolism of the posterior temporal lobes. Though some points remain obscure, we propose that a consolidation deficit hypothesis provides the most sensible interpretation of this peculiar pattern of memory deficit.