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Thalamo-cortical synchronization across the sleep-wake cycle: A combined fMRI/EEG study
Upon acoustic stimulation, negative BOLD fMRI responses of varying extent and intensity can be observed during sleep. In total, 7 subjects have been measured during nonREM sleep and 8 subjects during REM episodes. Negative BOLD responses during nonREM sleep, indicating neuronal deactivation, are likely to reflect a sleep protective mechanism. BOLD responses during REM sleep are qualitatively different between tonic REM sleep, when responses similar to wakefulness occur, and phasic REM sleep which goes along with prominent negative BOLD responses including thalamic deactivation. Functional connectivity maps which correlate thalamic and cortical fMRI responses show a strongly synchronized thalamo-cortical network in REM episods. This thalamocortical synchronization is far less pronounced during the other vigilance states. Combinig fMRI and EEG in sleep can provide new insights in alterations in brain reactivity and functional networks.