Sustained experience of emotion after loss of memory in patients with amnesia

Abstract

Can the experience of an emotion persist once the memory for what induced the emotion has been forgotten? We capitalized on a rare opportunity to study this question directly using a select group of patients with severe amnesia following circumscribed bilateral damage to the hippocampus. The amnesic patients underwent a sadness induction procedure (using affectively-laden film clips) to ascertain whether their experience of sadness would persist beyond their memory for the sadness-inducing films. The experiment showed that the patients continued to experience elevated levels of sadness well beyond the point in time at which they had lost factual memory for the film clips. A second experiment using a happiness induction procedure yielded similar results, suggesting that both positive and negative emotional experiences can persist independent of explicit memory for the inducing event. These findings provide direct evidence that a feeling of emotion can endure beyond the conscious recollection for the events that initially triggered the emotion.

Fig. 1.

Prototypical example of the severe bilateral hippocampal atrophy present in this cohort of amnesic patients. (Right) a coronal MRI image of patient Am4 and (Left) the homologous image from a healthy brain. The white arrows point to the region of the hippocampus.

Fig. 2.

Timeline of the experiment. Both inductions (sadness and happiness) followed the same timeline. The entire procedure lasted approximately 1 hour depending on the pace of the individual participant. The numbers shown represent the approximate time (in minutes) relative to the end of the film clips. T0, T1, T2, and T3 signify the four emotion measurements. The critical emotion measure for determining whether the emotional experience persisted beyond memory is the T2 emotion measure.

Fig. 3.

Recollection of film clips and postfilm emotion ratings following the sadness induction. (A) Total number of factual details recalled by each severe amnesic patient (Am1–Am5) along with the group mean for the normal comparison participants. (B) Average level of sadness reported by each group on a modified visual analog scale ranging from 0 (no emotion) to 100 (extreme emotion). Each score represents the change from baseline. All error bars represent the standard error of the mean. (C) Average negative and positive affect composite scores for each group. Each score represents the change from baseline using the percent of maximum possible (POMP).

Fig. 4.

Each participant's emotion ratings following the sadness induction for (A) level of sadness (VAS) and (B) total affect composite score. Each severe amnesic patient (Am1–Am5) is graphed alongside their matched normal comparison participant (NC1–NC5). Each score represents the change from baseline in POMP units. T1 is after induction, T2 is after memory, and T3 is the final rating.

Fig. 5.

Recollection of film clips and postfilm emotion ratings following the happiness induction. (A) Total number of factual details recalled by each severe amnesic patient (Am2-Am5) along with the group mean for the normal comparison participants. (B) Average level of amusement reported by each group on a modified visual analog scale ranging from 0 (no emotion) to 100 (extreme emotion). Each score represents the change from baseline. All error bars represent the standard error of the mean. (C) Average happiness and negative affect composite scores for each group. Each score represents the change from baseline using the percent of maximum possible (POMP).