How do we look while dreaming: binocular coordination of eye movements during REM sleep

In everyday life while shifting our gaze to objects of interest, our eyes are highly conjugated (Hering’s law, 1868). It is unknown whether binocular control is active during human REM sleep. Monkey REM sleep eye movements could be observed that did not follow Hering’s law. Recent human electrophysiological and functional imaging studies indicate active processing of dreamed images during REM sleep. Two different hypotheses exist: REMs (i) are indicators of spontaneous eye muscle contractions or (ii) reflect scanning dreamed images. We studied eye movements in REM sleep in six subjects using scleral search coils. Sleep EEG was recorded by a recording system which can be used in magnetic fields. Sleep stages were scored online; right within the third sleep phase we inserted scleral search coils in each eye and recorded eye movements within the next sleep period (for about two hours). Data show that the eyes move mainly conjugated during fast phases of REMs, but may diverge vertically and horizontally in sleep stages with slow roving eye movement. These results suggest that during N1 sleep, binocular coordination of roving eye movements is predominantly deactivated, probably due to missing parietal control. On the other hand during REM sleep, binocular control of rapid conjugate eye movements in the midbrain seems to stay awake.