The fate of old memories after medial temporal lobe damage

Abstract

Damage to the hippocampal region and related medial temporal lobe structures (perirhinal, entorhinal, and parahippocampal cortices) impairs new learning (anterograde amnesia) as well as memory for information that was acquired before the damage occurred (retrograde amnesia). We assessed retrograde amnesia with the Autobiographical Memory Interview (AMI) and with a news events test in six patients with damage limited primarily to the hippocampal region (H group) and two patients with large medial temporal lobe lesions (MTL group). On the news event test, the H group exhibited temporally limited retrograde amnesia covering approximately 5 years. On the same test, the MTL group exhibited an extensive retrograde amnesia covering decades. Nevertheless, performance was relatively spared for very remote time periods. On the AMI, all patients had intact remote autobiographical memory. Because our patients with hippocampal lesions, as well as our patients with large MTL lesions, performed normally on the AMI, patients who perform poorly on the same test presumably have damage beyond the hippocampus and related structures in the medial temporal lobe. The findings emphasize the difference in the extent of retrograde amnesia associated with hippocampal lesions and large MTL lesions.

Figure 1.

Performance on the Autobiographical Memory Interview. A, Scores on items that assessed factual knowledge about a person's own past (maximum score, 21). B, Scores on items that assessed memory for autobiographical events (maximum score, 9). Error bars indicate SEM.

Figure 2.

Recall performance on a test of news events that occurred from 1951 to 2005. The scores for six patients with damage limited primarily to the hippocampal region and 13 controls have been aligned relative to the onset of amnesia (see Materials and Methods) so that performance can be shown for the time period after the onset of amnesia and for 5 year intervals preceding the onset of amnesia (retrograde amnesia). The data point at −5 represents 1–5 years before amnesia, the point at −10 represents 6–10 years before amnesia, and so on. Error bars indicate SEM.

Figure 3.

Recall performance on a test of news events that occurred from 1938 to 2005 (E.P.) and from 1951 to 2005 (G.P.). The scores for the two patients with large medial temporal lobe lesions and seven controls have been aligned relative to the onset of amnesia (see Materials and Methods) so that performance can be shown for the time period after the onset of amnesia and for 5 year intervals preceding the onset of amnesia (retrograde amnesia). The data point at −5 represents 1–5 years before amnesia, the point at −10 represents 6–10 years before amnesia, and so on. Error bars indicate SEM.