The lack of temporal brain dynamics asymmetry as a signature of impaired consciousness states

Abstract

Life is a constant battle against equilibrium. From the cellular level to the macroscopic scale, living organisms as dissipative systems require the violation of their detailed balance, i.e. metabolic enzymatic reactions, in order to survive. We present a framework based on temporal asymmetry as a measure of non-equilibrium. By means of statistical physics, it was discovered that temporal asymmetries establish an arrow of time useful for assessing the reversibility in human brain time series. Previous studies in human and non-human primates have shown that decreased consciousness states such as sleep and anaesthesia result in brain dynamics closer to the equilibrium. Furthermore, there is growing interest in the analysis of brain symmetry based on neuroimaging recordings and since it is a non-invasive technique, it can be extended to different brain imaging modalities and applied at different temporo-spatial scales. In the present study, we provide a detailed description of our methodological approach, paying special attention to the theories that motivated this work. We test, for the first time, the reversibility analysis in human functional magnetic resonance imaging data in patients suffering from disorder of consciousness. We verify that the tendency of a decrease in the asymmetry of the brain signal together with the decrease in non-stationarity are key characteristics of impaired consciousness states. We expect that this work will open the way for assessing biomarkers for patients' improvement and classification, as well as motivating further research on the mechanistic understanding underlying states of impaired consciousness.

Navigating Pubertal Goldilocks: The Optimal Pace for Hierarchical Brain Organization

“…Harnessing the principles of thermodynamics, we quantified hierarchy by computing the level of irreversibility in brain signals during resting state conditions. Specifically, we captured the level of irreversibility through entropy production [ 51 , 53 , 56 , 57 , 85 ] as computed through a sophisticated clustering strategy. Note that resting states cover a rich range of the dynamical repertoire of the brain and thus those are ideal to characterize the most general and wide variety of interaction across the whole brain, i.e., the underlying hierarchical orchestration.…”

Dynamics of EEG Microstates Change Across the Spectrum of Disorders of Consciousness

“…Our results are aligned with previous observations which report higher entropy production with an increase in task cognitive demand 21 and a decrease in global states of unconsciousness 20 . Other analogous metrics have been proposed, where a breaking of temporal symmetry (analogous to the entropy production) is shown in healthy control compared to patients with a disorder of consciousness 37 .…”

Navigating Pubertal Goldilocks: The Optimal Pace for Hierarchical Brain Organization

“…Harnessing the principles of thermodynamics, we quantified hierarchy by computing the level of irreversibility in brain signals during resting state conditions. Specifically, we captured the level of irreversibility through entropy production 69,71,74,76,77 as computed through a sophisticated clustering strategy. Note that resting states cover a rich range of the dynamical repertoire of the brain and thus those are ideal to characterise the most general and wide variety of interaction across the whole brain, i.e., the underlying hierarchical orchestration.…”