Does sleep restore the topology of functional brain networks?

Abstract

Previous studies have shown that healthy anatomical as well as functional brain networks have small-world properties and become less optimal with brain disease. During sleep, the functional brain network becomes more small-world-like. Here we test the hypothesis that the functional brain network during wakefulness becomes less optimal after sleep deprivation (SD). Electroencephalography (EEG) was recorded five times a day after a night of SD and after a night of normal sleep in eight young healthy subjects, both during eyes-closed and eyes-open resting state. Overall synchronization was determined with the synchronization likelihood (SL) and the phase lag index (PLI). From these coupling strength matrices the normalized clustering coefficient C (a measurement of local clustering) and path length L (a measurement of global integration) were computed. Both measures were normalized by dividing them by their corresponding C-s and L-s values of random control networks. SD reduced alpha band C/C-s and L/L-s and theta band C/C-s during eyes-closed resting state. In contrast, SD increased gamma-band C/C-s and L/L-s during eyes-open resting state. Functional relevance of these changes in network properties was suggested by their association with sleep deprivation-induced performance deficits on a sustained attention simple reaction time task. The findings indicate that SD results in a more random network of alpha-coupling and a more ordered network of gamma-coupling. The present study shows that SD induces frequency-specific changes in the functional network topology of the brain, supporting the idea that sleep plays a role in the maintenance of an optimal functional network.

Assessing cortical synchronization during transcranial direct current stimulation: A graph-theoretical analysis

“…In any case, the disagreement between the two measures must be interpreted also as a caution signal towards the reliability of short connections modulation, and in this sense combining different measures is recommended. Previously, a combined phase-lag and SL study showed a large overlap between the two indices (Koenis et al, 2013), supporting the idea that SL is unlikely to be affected by volume conduction. Further studies are necessary to clarify the possibility of volume conduction effects on SL as well as to compare SL and phase lag indices.…”

The role of sleep electroencephalography in patients with new onset epilepsy

“…One explanation may be the increased variability in cortical excitability during sleep [28], which may originate from an altered functional network organization following sleep deprivation [29]. A mechanism, such as increased synchronization during sleep and after sleep deprivation, may also be a reflection of increased cortical excitability [30,31].…”

Opportunities and methodological challenges in EEG and MEG resting state functional brain network research

“…The state 'drowsiness' is often avoided in resting state research, because alertness or wakefulness is reduced during a drowsiness state and may vary and influence measurements greatly. However, recognizing drowsiness in resting state recordings can be difficult and requires a systematic approach (Koenis et al , 2013, van Diessen et al , 2014. Each state of vigilance has specific characteristics that contribute to differences in spectral power (Niedermeyer et al , 1987, Cantero et al , 1999 and functional connectivity (Kuhnert et al , 2010.…”