FUNCTIONAL AND STRUCTURAL NEUROIMAGING CORRELATES OF SELECTIVE RETROGRADE-AMNESIA - A CASE-STUDY WITH MRI AND PET

The neuroanatomical and neurophysiological systems underlying episodic memory functioning were assessed in a case of retrograde amnesia with out anterograde amnesia following traumatic brain injury (TBT). MRI sh owed evidence of a focal right inferior frontal injury affecting both cortical tissue and frontal-subcortical pathways, including the uncina te fasciculus, a frontal-temporal band of fibers previously hypothesiz ed to be involved in retrieval of personal episodic memories. On an (H 2O)-O-15 PET activation paradigm that reliably elicits right frontal a ctivation on retrieval and left frontal activation on encoding, the in dex case did not show increased right frontal activation on retrieval. The normal pattern of right frontal activation was observed in a matc hed TBI control subject without retrograde amnesia. Both the index cas e and the matched control showed additional posterior activations whic h suggested TBI-related disinhibition, compensation, or both. Taken to gether, the neuroimaging findings converge to suggest a right frontal- temporal system mediating retrieval of episodic memories.