Amnesia as an impairment of detail generation and binding: evidence from personal, fictional, and semantic narratives in K.C.

Autobiographical episodic recall involves active simultaneous generation and binding of various elements that were present during the initial experience. Deficits in this reconstructive process may account for some aspects of retrograde amnesia (RA) for personally experienced events. Constructive and reconstructive processes may involve similar mechanisms. If so, patients with extensive anterograde amnesia (AA) and RA should show deficits in non-recollective cognitive domains, such as imagining events that had never been experienced and recounting non-personal narratives, that presumably rely on constructive and re-constructive processes, respectively. To test these possibilities, patient K.C., who has severe AA and RA for personal episodes, was asked to generate fictional events and to recall and recognize details of well-known fairy tales and bible stories. K.C.'s performance on both tasks was better than expected given his severely impaired autobiographical episodic memory (AM), but significantly worse than that of control participants. K.C. was able to create a skeletal outline for both types of narratives, providing sufficient information to convey their gist, but the narratives were fragmented and lacking in detail. This deficit cannot be explained as resulting entirely from deficient stored semantic knowledge, because K.C. was able to discriminate between true and false details of non-personal semantic narratives on a recognition test, which he cannot do for personal events [Gilboa, A., Winocur, G., Rosenbaum, R.S., Poreh, A., Gao, F., Black, S.E., Westmacott, R., & Moscovitch, M. (2006a). Hippocampal contributions to recollection in retrograde and anterograde amnesia. Hippocampus, 16, 966-980]. Thus, retrograde AM impairment may be viewed as both a loss of information as well as a deficit in reconstructive processes that hamper or prevent the binding of information to generate a cohesive, detail-rich memory.