Functional MRI of sleep spindles and K-complexes

Abstract

Objective Sleep 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. Methods EEGs 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. Result fMRI 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. Conclusions fMRI 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. Significance Identification of these active regions contributes to the understanding of sleep networks and the physiology of awareness and memory during sleep.

Sleep Neuroimaging and Models of Consciousness

“…Combined EEG-fMRI studies show that the BOLD correlates of K-complexes comprise multimodal sensory areas as well as key regions in the DMN (e.g., the precuneus) (Caporro et al, 2012; Jahnke et al, 2012) (the resulting activation patterns are shown in Figure 1B), which is consistent with the latter proposed function (brief periods of a “wakefulness-like” brain state).…”

Sleep spindle alterations in patients with Parkinson's disease

“…The three oldest male control subjects have negligible SS densities. These observations suggest that reduced SS density is not specific for PD, in agreement with the fact that many conditions such as cognitive function, memory consolidation, pharmacological interventions and pre-PSG conditions have been reported to influence SS density (De Gennaro and Ferrara, 2003;Caporro et al, 2012). Further analysis including more PD and iRBD patients, together with a more in-depth investigation of cognitive decline and disease severity would be needed to evaluate the relation of abnormalities in SS development in the disease process, and the use of SS as a prognostic marker.…”

An intra-K-complex oscillation with independent and labile frequency and topography in NREM sleep

“…Earlier reports by Peter Halasz and colleagues that KCs express a double nature (Janus-face) (Colrain, 2005; Halász and Bodizs, 2013) are supported by recent fMRI evidence of sensory areas involvement in KCs (Caporro et al, 2012; Jahnke et al, 2012) and even the spontaneous KCs wear at their initial segment the traces of multisensory processing (Riedner et al, 2011). It is thus suggested that “K-complex embodies an arousal with subsequent sleep guarding counteraction that might on one hand serve monitoring of the environment with basic information processing and on the other hand protect continuity of sleep and thus its restoring effect” (Jahnke et al, 2012).…”