Functional MRI of sleep spindles and K-complexes

ObjectiveSleep spindles and K-complexes are EEG hallmarks of non-REM sleep. However, the brain regions generating these discharges and the functional connections of their generators to other regions are not fully known. We investigated the neuroanatomical correlates of spindles and K-complexes using simultaneous EEG and fMRI.MethodsEEGs recorded during EEG-fMRI studies of 7 individuals were used for fMRI analysis. Higher-level group analyses were performed, and images were thresholded at Z ⩾ 2.3.ResultsfMRI of 106 spindles and 60 K-complexes was analyzed. Spindles corresponded to increased signal in thalami and posterior cingulate, and right precuneus, putamen, paracentral cortex, and temporal lobe. K-complexes corresponded to increased signal in thalami, superior temporal lobes, paracentral gyri, and medial regions of the occipital, parietal and frontal lobes. Neither corresponded to regions of decreased signal.ConclusionsfMRI of both spindles and K-complexes depicts signal subjacent to the vertex, which likely indicates each discharges’ source. The thalamic signal is consistent with thalamic involvement in sleep homeostasis. The limbic region’s signal is consistent with roles in memory consolidation. Unlike the spindle, the K-complex corresponds to extensive signal in primary sensory cortices.SignificanceIdentification of these active regions contributes to the understanding of sleep networks and the physiology of awareness and memory during sleep.

► Sleep spindles and K-complexes are features specific to non-REM sleep that may be related to sleep homeostasis and memory consolidation.
► The full extent of brain regions active during their occurrences is not known.
► Simultaneous EEG and functional MRI identified activity in the thalamus and temporal lobe for both discharges and additional regions in sensory cortex for the K-complex.