Despite accumulating evidence for a reconsolidation process in animals, support in humans, especially for episodic memory, is limited. Using a within-subjects manipulation, we found that a single application of electroconvulsive therapy following memory reactivation in patients with unipolar depression disrupted reactivated, but not non-reactivated, memories for an emotional episode in a time-dependent manner. Our results provide evidence for reconsolidation of emotional episodic memories in humans.
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- Supplementary Figure 1: Study design. (33 KB)
Patients were assigned to one of three groups (A, B, C). During a first study session all groups were shown two emotional slide-show stories. During a second session memory for one of the two stories was reactivated. Immediately after memory reactivation patient in groups A and B received ECT. In patients of group B memory was tested immediately upon recovery from ECT (Test, blue). In patients of groups A and C memory was tested one day after reactivation (Test, red and orange respectively).
- Supplementary Figure 2: Stimulus material (569 KB)
Patients were presented with two slide shows that form arousing episodic stories of negative valence. Top: the original “Cahill Story”, bottom: the newly developed story. Both stories consist of 11 slides and each slide is accompanied by an auditory narrative.
- Supplementary Figure 3: Memory reactivation scores (25 KB)
All groups showed evidence of memory reactivation, i.e., memory performance at reactivation was above chance level as indexed by the memory reactivation score (one-sample t-test across all groups, (t(36) = 7.53, P < 0.001), and groups did not differ in memory reactivation scores (y-axis; Kruskal-Wallis for group (A,B,C), H(2) = 1.77, P = 0.412; group A (red) mean: 3.08, s.e.m.: 0.35; group B (blue): mean: 2.62, s.e.m.: 0.96; group C (orange) mean: 3.23; s.e.m.: 1.24). Therefore, the observed between-group differences in reactivated memories are not due to differences in strength of memory reactivation, and adequate memory reactivation principally allows the initiation of a reconsolidation process. Dashed line indicates chance level (25%), error bars depict s.e.m.
- Supplementary Figure 4: DSST results (30 KB)
DSST scores in minutes (y-axis). A group (A, B, C) x time point (study, test) repeated measures ANOVA on DSST scores revealed no main effect of time point (F1, 33 = 1.72, P = 0.199), group (F2, 33 = 0.69, P = 0.509) or group x time point interaction (F2, 33 = 1.64, P = 0.209). Thus, General cognitive functioning does not differ between groups. Hence, group differences in memory performance are unlikely to be due to group differences in general cognitive functioning. Error bars depict s.e.m.
- Supplementary Figure 5: Story phase results (33 KB)
Memory scores (y-axis) per phase for group A. Emotional narratives accompanied both slide-stories learnt by patients. Each story can be separated into three phases (x-axis) of which the middle is considered most emotional and results in enhanced memory when compared to the same images accompanied by a neutral narrative. Testing for a reactivation (reactivated story (solid bars), non-reactivated story (open-bars)) x phase (1,2,3) effect within group A revealed a main effect of reactivation (F1, 12 = 8.75 P = 0.012), but no main effect of phase (F2, 24 = 0.48, P = 0.624), or reactivation x phase interaction (F2, 24 = 2.40, P = 0.112). Thus we observe no interaction between relative emotionality of the studies material and the disturbance of reactivated memory. Error bars depict s.e.m.
- Supplementary Figure 6: Memory performance is associated with illness and ECT parameters (67 KB)
We assessed whether screening scores or elements of ECT treatment were related to memory performance. Top: Cumulative illness rating scale scores (CIRS, y-axis) correlated with memory performance (x-axis) over all groups (Pearson r = –0.32, N = 38, P = 0.047), thus the lower the comorbid physical problems or illnesses the better memory performance. Middle: Limiting the analyses to group A and group B, we tested whether ECT treatment parameters were related to memory performance. An independent t-test showed that memory impairment was greater for bifrontotemporal electrode placement compared to right unilateral stimulation (t(24) = 2.28, P = 0.032, right unilateral mean: 36.27, s.e.m: 2.45; bifrontotemporal mean: 28.91, s.e.m.: 1.96). Bottom: Given that bilateral stimulation leads to more memory impairment, we specifically tested for a modulation of reconsolidation by electrode placement in group A. No effect was observed (P > 0.05), but this null finding may reflect the size of our sample (unilateral N=4, bilateral N=9). The reconsolidation impairment observed in group A was still evident when controlling for electrode placement. The relation between electrode placement and memory performance suggests that the observed memory impairments are a result of the electrical stimulation and/or the convulsion itself and not other elements of the ECT treatment such as the anaesthesia. Error bars depict s.e.m.
- Supplementary Text and Figures (2,034 KB)
Supplementary Figures 1–6, Supplementary Tables 1 and 2