Several brain regions and physiological processes have been proposed to constitute the neural correlates of consciousness. In this Review, Koch and colleagues discuss studies that distinguish the neural correlates of consciousness from other neural processes that precede, accompany or follow it, and suggest that the neural correlates of consciousness are localized to posterior cortical regions.

Neural correlates of consciousness: progress and problems

Regional Slow Waves and Spindles in Human Sleep

Decoding Wakefulness Levels from Typical fMRI Resting-State Data Reveals Reliable Drifts between Wakefulness and Sleep

Graph theoretical analysis of functional magnetic resonance imaging (fMRI) time series has revealed a small-world organization of slow-frequency blood oxygen level-dependent (BOLD) signal fluctuations during wakeful resting. In this study, we used graph theoretical measures to explore how physiological changes during sleep are reflected in functional connectivity and small-world network properties of a large-scale, low-frequency functional brain network. Twenty-five young and healthy participants fell asleep during a 26.7 min fMRI scan with simultaneous polysomnography. A maximum overlap discrete wavelet transformation was applied to fMRI time series extracted from 90 cortical and subcortical regions in normalized space after residualization of the raw signal against unspecific sources of signal fluctuations; functional connectivity analysis focused on the slow-frequency BOLD signal fluctuations between 0.03 and 0.06 Hz. We observed that in the transition from wakefulness to light sleep, thalamocortical connectivity was sharply reduced, whereas corticocortical connectivity increased; corticocortical connectivity subsequently broke down in slow-wave sleep. Local clustering values were closest to random values in light sleep, whereas slow-wave sleep was characterized by the highest clustering ratio (gamma). Our findings support the hypothesis that changes in consciousness in the descent to sleep are subserved by reduced thalamocortical connectivity at sleep onset and a breakdown of general connectivity in slow-wave sleep, with both processes limiting the capacity of the brain to integrate information across functional modules.

https://www.jneurosci.org/content/jneuro/30/34/11379.full.pdf

Development of a Large-Scale Functional Brain Network during Human Non-Rapid Eye Movement Sleep

https://stacks.cdc.gov/view/cdc/30150/cdc_30150_DS1.pdf

State-Dependent Architecture of Thalamic Reticular Subnetworks

Thalamic and cortical activities are assumed to be time-locked throughout all vigilance states. Using simultaneous intracortical and intrathalamic recordings, we demonstrate here that the thalamic deactivation occurring at sleep onset most often precedes that of the cortex by several minutes, whereas reactivation of both structures during awakening is synchronized. Delays between thalamus and cortex deactivations can vary from one subject to another when a similar cortical region is considered. In addition, heterogeneity in activity levels throughout the cortical mantle is larger than previously thought during the descent into sleep. Thus, asynchronous thalamo-cortical deactivation while falling asleep probably explains the production of hypnagogic hallucinations by a still-activated cortex and the common self-overestimation of the time needed to fall asleep.

https://www.pnas.org/content/pnas/107/8/3829.full.pdf

Thalamic deactivation at sleep onset precedes that of the cerebral cortex in humans

Study objectives: Using spectral edge frequency (SEF 95 ) and dimension of activation (DA), a new tool derived from the dimension of correlation, we assessed the activation of thalamus and cortex in the different vigilance states. Patients: Results were gathered from intracerebral recordings performed in 12 drug-resistant epileptic patients during video-stereoelectroencephalographic (SEEG) monitoring. Results: In the cortex, we observed a progressive decrease of DA from wake to sleep, with minimal DA values characterizing the deep slow wave sleep (dSWS) stage. During paradoxical sleep (PS), cortical level of activity returned to DA values similar to those obtained during wakefulness. In the thalamus, DA values during wakefulness were higher than the values observed during light SWS (lSWS), deep SWS (dSWS) and PS; there were no significant differences between the 3 sleep stages. Similar variations were observed with SEF 95 . Conclusion: DA analysis proved reliable for quantification of cortical activity, in agreement with data issued from classical vigilance states scoring and spectral analysis. At the thalamic level, only 2 levels of activity within a sleep wake cycle were observed, pointing to dissociated levels of activation between the thalamus and the neocortex during lSWS and PS.

/pdf/human-thalamic-and-cortical-activities-assessed-by-dimension-1psk7979nt.pdf

Human thalamic and cortical activities assessed by dimension of activation and spectral edge frequency during sleep wake cycles.

Procede d'analyse d'un signal d'eeg-fractoimageur

The invention concerns a method for analysing one signal or several simultaneous signals, comprising steps which consist in converting into digital samples the successive values of the signal(s); forming in a discretized space of dimension d a scatter diagram of n dots each of which has d co-ordinates taken regularly among the successive samples of the signal(s); partitioning the space of dimension d into hypercubes; and computing the distances between the dots inside each hypercube.

Method for analyzing an EEG signal

The invention concerns a method for analysing one signal or several simultaneous signals, comprising steps which consist in converting into digital samples the successive values of the signal(s); forming in a discretized space of dimension d a scatter diagram of n dots each of which has d co-ordinates taken regularly among the successive samples of the signal(s); defining a single line passing through all the dots of the space, said line being such that dots close in the space are close in rank on the line; and in operating upon the ranks of the dots on said line to supply data representing the analysed signal(s), such as the correlation dimension.

Philippe Guillemant

Papers

Thalamic deactivation at sleep onset precedes that of the cerebral cortex in humans

Human thalamic and cortical activities assessed by dimension of activation and spectral edge frequency during sleep wake cycles.

Procede d'analyse d'un signal d'eeg-fractoimageur

Method for analyzing an EEG signal

Method for analysing a phase-spacing-eeg