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. 2016 Nov 22;113(47):13480-13485.
doi: 10.1073/pnas.1617025113. Epub 2016 Nov 7.

Learning and remembering real-world events after medial temporal lobe damage

Adam J O Dede  1   2 , Jennifer C Frascino  1   3 , John T Wixted  2 , Larry R Squire  4   2   3   5
Affiliations
Free PMC article

Learning and remembering real-world events after medial temporal lobe damage

Adam J O Dede et al. Proc Natl Acad Sci U S A. .
Free PMC article

Abstract

The hippocampus is important for autobiographical memory, but its role is unclear. In the study, patients with hippocampal damage and controls were taken on a 25-min walk on the University of California, San Diego, campus during which 11 planned events occurred. Memory was tested directly after the walk. In addition, a second group of controls took the same walk and were tested after 1 mo. Patients with hippocampal damage remembered fewer details than controls tested directly after the walk but remembered a similar number of details as controls tested after 1 mo. Notably, the details that were reported by patients had the characteristics of episodic recollection and included references to particular places and events. Patients exhibited no special difficulty remembering spatial details in comparison with nonspatial details. Last, whereas both control groups tended to recall the events of the walk in chronological order, the order in which patients recalled the events was unrelated to the order in which they occurred. The findings illuminate the role of the hippocampus in autobiographical memory and in the spatial and nonspatial aspects of episodic recollection.

Keywords: autobiographical memory; hippocampus; prospective memory.

Conflict of interest statement

The authors declare no conflict of interest.

Figures

Fig. 1.
Fig. 1.
Map of 11 events that occurred during a 25-min guided walk. 1: discard a cup. 2: find change in a vending machine. 3: view portraits of department chairs. 4: point out coffee cart. 5: find book on the second floor of the library. 6: receive bike lock from student. 7: lock up bike. 8: view statue. 9: buy banana in cafe. 10: stop to tie shoes. 11: drink from water fountain. Sidewalks are light gray. Buildings are dark gray. Arrows indicate the path taken during the walk.
Fig. 2.
Fig. 2.
Number of accurate details produced during a 6-min narrative description of events that occurred during a 25-min walk. (A) Details were assigned to one of four categories according to their content. (B) The number of details that were repeated during the narrative. CON-1, controls tested directly after the walk. CON-2, controls tested 1 mo after the walk. H, patients with hippocampal lesions. MTL, a patient with large medial temporal lobe lesions. Error bars show SEM.
Fig. 3.
Fig. 3.
The data points show when, on average, the events from the walk were described during the 6-min narratives. The two control groups tended to describe events in the order that they occurred. The order in which the patients described events was unrelated to the order in which the events occurred. Lines represent significant fits to the data. (A) The patients described only 9 of the 11 events, and no patient described events 10 and 11. Black squares: CON-1, controls tested directly after the walk. Open triangles: H, patients with hippocampal lesions plus MTL, a patient with large medial temporal lobe lesions. (B) CON-1 (black squares) together with controls tested 1 mo after the walk (CON-2, open circles). The CON-2 group described only 10 of the 11 events, and no CON-2 described event 1.
Fig. 4.
Fig. 4.
Number of accurate details produced in 1-min narratives when participants were asked about each event separately in response to a prompt. The data are arranged according to how well the CON-1 group remembered each event. CON-1, controls tested directly after the walk. CON-2, controls tested 1 mo after the walk. H, patients with hippocampal lesions. MTL, a patient with large medial temporal lobe lesions. Error bars show SEM.
Fig. 5.
Fig. 5.
Details recalled during 1-min narratives about each event in response to a prompt (also see Fig. 4). The events best remembered by CON-1 were also the events best remembered by the H and MTL patients. The numbers identify each event (Fig. 1). The scatter plot shows the mean number of accurate details per event produced by the patients as a function of the mean number of details produced by CON-1. For example, CON-1 recalled 7.1 details about event 4 (coffee cart) and 10.4 details about event 5 (library). The patients recalled 1.8 and 6.2 details about these same two events. CON-1, controls tested directly after the walk. H, patients with hippocampal lesions. MTL, a patient with large medial temporal lobe lesions.
Fig. 6.
Fig. 6.
Performance on a test of 40 two-alternative, forced-choice questions about the events from the walk. There were four types of questions, querying different types of information. CON-1, controls tested directly after the walk. CON-2, controls tested 1 mo after the walk. H, patients with hippocampal lesions. MTL, a patient with large medial temporal lobe lesions. Error bars show SEM. Horizontal line represents chance performance.
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