Different brain reactivity during phasic and tonic REM sleep: A simultaneous FMRI and EEG study

Studies using functional magnetic resonance imaging (fMRI) have recently described changes of brain activity upon stimulation in NREM sleep. Making use of the novel approach of combined EEG and fMRI investigations in sleep, the objective of the present study was to explore regional activation patterns upon acoustic stimulation in REM sleep.

REM sleep scans could be obtained in eight of eleven subjects. Activation maps strongly differed between scans containing mainly tonic REM sleep and those dominated by phasic activity like rapid eye movements. Deactivation in the thalamus was seen only in phasic REM scans, along with synchronized deactivation of large cortical areas. In contrast, task-dependent activation patterns in tonic REM sleep were often similar to wakefulness. This first fMRI study on information processing in stage REM shows a difference in brain reactivity between tonic and phasic REM sleep.