Functional imaging of sleep

Sleep has traditionally been monitored by electrophysiological means such as electroencephalography. Nuclear medicine tracer methods such as SPECT and PET have previously been used to successfully assess changes in cerebral blood flow and metabolism occurring during sleep and provide little spatial resolution. These have only been able to document a short period of time. Functional Magnetic Resonance Imaging (fMRI) has established itself as the method of choice for non-invasive imaging of brain functions and can now also be performed with continuous EEG recording. Technical problems had to be resolved before fMRI could be applied to sleep successfully: indeed patient motion and scanner noise were major parts of these concerns. However, with optimisation of fMRI technology a few reports concerning the use of fMRI in sleep have surfaced recently. One approach has been to use a silent MR sequence (BURST) which provides robust fMRI data with a BOLD signal. We found occipital activation and frontal deactivation during REM sleep. Thus fMRI now seems to be applicable to sleep also which should provide sleep researchers with a new method for investigation in vivo of sleep physiology and pathology. The question of data evaluation still needs to be elucidated, however.