Evidence of an active role of dreaming in emotional memory processing shows that we dream to forget

Abstract

Dreaming is a universal human behavior that has inspired searches for meaning across many disciplines including art, psychology, religion, and politics, yet its function remains poorly understood. Given the suggested role of sleep in emotional memory processing, we investigated whether reported overnight dreaming and dream content are associated with sleep-dependent changes in emotional memory and reactivity, and whether dreaming plays an active or passive role. Participants completed an emotional picture task before and after a full night of sleep and they recorded the presence and content of their dreams upon waking in the morning. The results replicated the emotional memory trade-off (negative images maintained at the cost of neutral memories), but only in those who reported dreaming (Dream-Recallers), and not in Non-Dream-Recallers. Results also replicated sleep-dependent reductions in emotional reactivity, but only in Dream-Recallers, not in Non-Dream-Recallers. Additionally, the more positive the dream report, the more positive the next-day emotional reactivity is compared to the night before. These findings implicate an active role for dreaming in overnight emotional memory processing and suggest a mechanistic framework whereby dreaming may enhance salient emotional experiences via the forgetting of less relevant information.

Figure 1

Study Protocol. At 8 PM, participants encoded images from the EPT, emotional picture task, followed by an immediate test. Next, participants slept either at home or in the lab depending on their method of testing being remote or in-person, respectively. Upon awaking, participants reported the presence and description of their dreams and completed a delayed EPT test.

Figure 2

Emotional picture task (EPT) schematic.

Figure 3

Comparing in-lab and remote participants’ memory performance at Test 1 (immediate), Test 2 (delayed), and overnight change (Test 2–Test 1) for (a) negative (Test 1 t₁₂₂ = 3.50, p < 0.01; Test 2 t₁₂₂ = 2.17, p < 0.03) and (b) neutral pictures (Test 1 t₁₂₂ = 2.75, p < 0.01; Test 2 t₁₂₂ = 3.11, p < 0.01). Despite the significant differences between in-lab versus remote memory performance at Test 1 and Test 2, the overnight change in memory, for both negative and neutral pictures, was not different between in-person and remote participants.

Figure 4

Emotional memory trade-off (d prime in overnight memory change) for negative and neutral pictures for Dream-Recallers and Non-Dream-Recallers. The trade-off effect is shown as negative images maintained at the cost of neutral memories. We found a significant interaction Dream Recalls and Picture Valence (F(1,95) = 4.29, p = 0.04). Post hoc tests using Bonferroni suggest Dream-Recallers had less forgetting for negative pictures (M = − 0.22 ± 0.83) compared to neutral (M = − 0.63 ± 0.88) (mean difference = 0.41, t₉₄ = 2.96, p = 0.02), a pattern not seen in Non-Dream-Recallers (mean difference = 0.04, t₉₄ = 0.30, p = 1).

Figure 5

Association between total sleep time (TST) and overnight change in d’ for negative images for (a) non-dream-recallers and (b) dream-recallers. (a) A positive correlation between TST and overnight d’ change for negative pictures indicates longer sleep duration is associated with better overnight memory consolidation for negative images in non-dream-recallers (r = 0.37, p = 0.005). (b) No significant correlation between TST and overnight d’ change was found for dream-recallers (r = 0.15, p = 0.32),

Figure 6

Emotional valence change for negative and neutral pictures for Dream-Recallers and Non-Dream-Recallers. Dream-Recallers showed a significant decrease in valence for negative pictures compared to non-Dream-Recallers (t₁₂₀ = 2.50, p = 0.01), but no difference for neutral pictures (t₁₂₀ = 0.43, p = 0.67). Both Dream-Recallers (t₅₀ = − 4.85, p < 0.001) and Non-Dream-Recallers (t₇₀ = − 3.52, p < 0.001) also showed greater decreases in valence for negative compared to neutral pictures.

Figure 7

Emotional arousal change for negative and neutral pictures for Dream-Recallers and Non-Dream-Recallers. Dream-Recallers showed a significant decrease in arousal for negative pictures compared to non-Dream-Recallers (t₁₂₀ = 2.40, p < 0.02), but no difference for neutral pictures (t₁₂₀ = 0.10, p = 0.92). Dream-Recallers also showed a significant decrease in arousal for negative compared to neutral pictures (t₅₀ = − 2.91, p < 0.005), a pattern no shown in Non-Dream-Recallers (t₇₀ = − 0.34, p = 0.73).

Figure 8

Association between dream mood and change in emotional valence. (a) A negative correlation between dream mood and overnight valence change for neutral pictures indicates more positive dreams are associated with more reduction in valence rating (rho = − 0.31, p = 0.03). (b) No significant correlation between dream mood and change in emotional valence was found for negative pictures (rho = − 0.08, p = 0.60).