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

Summary

Living systems must constantly work against equilibrium to survive, a property that can be measured through temporal asymmetry in brain signals. Using statistical physics, researchers analyzed reversibility in functional magnetic resonance imaging data from patients with disorders of consciousness. They found that decreased asymmetry and reduced non-stationarity in brain signals characterize impaired consciousness states, consistent with previous findings in sleep and anesthesia. The work aims to identify biomarkers for patient improvement and classification, and to deepen mechanistic understanding of consciousness disorders.

Study at a glance

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.