FIGURE 1. Temporal variations in access to memory sources.

Temporal plots of memory sources of a dramatic event shown in a film appearing in dreams conform to a U-shape. This is consistent with the notion that dreams draw upon memories at different stages of consolidation and from different regions of the brain. A decreasing gradient of access to memories of a given event across the first three nights (recent residues) may correspond to hippocampally mediated memories, whereas an increasing gradient of access to memories from days 5–7 (delayed residues) may correspond to neocortically mediated memories. a, Repeated measures design. Exposure to a distressing film about ceremonial sacrifice of a water buffalo produces a U-shaped curve of incorporation likelihood scores across the week for high, but not low, incorporators (data from ref. 41). b, Incorporation likelihood scores across the week for nine subjects in the film study who were 'high incorporators', that is, whose dreams were assigned at least one score of 10 on the 0–10 incorporation scale. The U-shaped pattern is apparent in individual subjects' scores. Empty columns indicate that no dream was recalled. c, Randomized between-groups design. A U-shaped curve in dream–event correspondence ratings is also observed when subjects randomized to seven different groups search for memory sources from only one of the seven days before their dream and rate their confidence in these sources as high; that is, 5 or greater on a 0–9 scale (data from ref. 18).