Eye movements during REM sleep and imagination of visual scenes.

It has been hypothesized that rapid eye movements (REMs) during sleep reflect the process of looking around in dreams. We questioned whether REMs differ from eye movements in wakefulness while imagining previously seen visual stimuli (dots, static images, videos). After looking at these stimuli individuals were asked to remember and imagine them. Subsequently, their REMs were recorded at the sleep laboratory. Kinematic parameters of REMs were similar to saccadic eye movements to remembered stimuli with closed eyes, irrespective of the stimulus type. In contrast, peak velocity of eye movements with open eyes was similar to REMs when semantic, but not nonsemantic, contents were imagined. Thus, REMs may be related to exploratory saccadic behaviour in the awake to remember visual stimuli.