A cognitive process occurring during sleep revealed by rapid eye movements

Rapid eye movements during REM sleep reveal the direction and amplitude of gaze shifts in the virtual environment of dreams. By recording head direction cells in the thalamus of mice, researchers found that these eye movements encode the animal's virtual heading as it navigates its dream world. The findings indicate that eye movements during REM sleep are not random brainstem activity but instead reflect the cognitive processes of the sleeping brain, providing a window into dream content.

Study at a glance

Abstract

Since the discovery of rapid eye movement (REM) sleep, the nature of the eye movements that characterize this sleep phase has remained elusive. Do they reveal gaze shifts in the virtual environment of dreams or simply reflect random brainstem activity? We harnessed the head direction (HD) system of the mouse thalamus, a neuronal population whose activity reports, in awake mice, their actual HD as they explore their environment and, in sleeping mice, their virtual HD. We discovered that the direction and amplitude of rapid eye movements during REM sleep reveal the direction and amplitude of the ongoing changes in virtual HD. Thus, rapid eye movements disclose gaze shifts in the virtual world of REM sleep, thereby providing a window into the cognitive processes of the sleeping brain. Description The meaning of rapid eye movement Sleep includes phases characterized by rapid eye movement (REM) that were known to be associated with dreaming. But are these eye movements related to the contents of consciousness in that sleep state? Senzai and Scanziani recorded head direction cells in the anterior dorsal nucleus of the thalamus in mice during wake and sleep (see the Perspective by De Zeeuw and Canto). The direction and amplitude of rapid eye movements encoded the direction and amplitude of the heading of mice in their virtual environment during REM sleep. It was possible to predict the actual heading in the real and virtual world of the mice during wake and REM sleep, respectively, using saccadic eye movements. —PRS Rapid eye movements during REM sleep represent gaze shifts in the virtual world of the sleeping brain.