Autobiographical memory, future imagining, and the medial temporal lobe

Significance We explored the role of the medial temporal lobe (MTL) in autobiographical remembering and future imagining. Patients with MTL damage and controls produced narratives in four time periods (past and future). Findings showed that anterograde amnesia (forgetfulness) can interfere with narrative construction. Under conditions that minimized the effect of anterograde amnesia, patients produced as many details as controls in five different content categories (spatial and nonspatial) and in all time periods except the recent past. The results suggest that remembering the remote past and imagining the future are independent of the MTL. Comparisons among studies suggest that differences in performance likely depend on differences in the locus and extent of brain damage. In two experiments, patients with damage to the medial temporal lobe (MTL) and healthy controls produced detailed autobiographical narratives as they remembered past events (recent and remote) and imagined future events (near and distant). All recent events occurred after the onset of memory impairment. The first experiment aimed to replicate the methods of Race et al. [Race E, Keane MM, Verfaellie M (2011) J Neurosci 31(28):10262–10269]. Transcripts from that study were kindly made available for independent analysis, which largely reproduced the findings from that study. Our patients produced marginally fewer episodic details than controls. Patients from the earlier study were more impaired than our patients. Patients in both groups had difficulty in returning to their narratives after going on tangents, suggesting that anterograde memory impairment may have interfered with narrative construction. In experiment 2, the experimenter used supportive questioning to help keep participants on task and reduce the burden on anterograde memory. This procedure increased the number of details produced by all participants and rescued the performance of our patients for the distant past. Neither of the two patient groups had any special difficulty in producing spatial details. The findings suggest that constructing narratives about the remote past and the future does not depend on MTL structures, except to the extent that anterograde amnesia affects performance. The results further suggest that different findings about the status of autobiographical memory likely depend on differences in the location and extent of brain damage in different patient groups.