Temporal irreversibility of neural dynamics as a signature of consciousness

Abstract

Even though the fundamental laws of physics are the same when the direction of time is inverted, dissipative systems evolve in the preferred temporal direction indicated by the thermodynamic arrow of time. The fundamental nature of this temporal asymmetry led us to hypothesize its presence in the neural activity evoked by conscious perception of the physical world, and thus its covariance with the level of conscious awareness. Inspired by recent developments in stochastic thermodynamics, we implemented a data-driven and model-free deep learning framework to decode the temporal inversion of electrocorticography signals acquired from non-human primates. Brain activity time series recorded during conscious wakefulness could be distinguished from their inverted counterparts with high accuracy, both using frequency and phase information. However, classification accuracy was reduced for data acquired during deep sleep and under ketamine-induced anesthesia; moreover, the predictions obtained from multiple independent neural networks were less consistent for sleep and anesthesia than for conscious wakefulness. Finally, the analysis of feature importance scores highlighted transitions between slow (≈20 Hz) and fast frequencies (> 40 Hz) as the main contributors to the temporal asymmetry observed during conscious wakefulness. Our results show that a preferred temporal direction is simultaneously manifest in the neural activity evoked by conscious mentation and in the phenomenology of the passage of time, establishing common ground to tackle the relationship between brain and subjective experience.

The time scales of irreversibility in spontaneous brain activity are altered in obsessive compulsive disorder

“…Even in very simple systems, different coarse-graining procedures can influence the information loss on the original system in different ways and lead to very different estimates on the entropy production (128,130,131). Despite these caveats, the quantification of irreversibility remains a useful way of characterizing the system's dynamical properties and the empirical evidence that time-reversal symmetry breaking is modulated by pathologies and even behavioral states corroborates this view (56)(57)(58)(59)(60).…”

“…Consistent with the role of nonlinearity and its inherently out-of-equilibrium nature, spontaneous brain activity has long been associated with marked time reversal symmetry breaking (55). The magnitude of irreversibility is characterized by temporal fluctuations and is modulated in a task-specific way (56,57), with greater values for task-related relative to resting brain activity (57), and wakefulness relative to in deep anesthesia (58). Irreversibility of resting brain activity has also been shown to be altered in various neurological and psychiatric pathologies, including epilepsy (56,59,60), attention deficit hyperactivity disorder (57), Alzheimer's disease (56), Parkinson's disease (56), bipolar disorder (57), and schizophrenia (56,57).…”

Algorithmic Approaches for Assessing Irreversibility in Time Series: Review and Comparison

“…Resting brain activity has been shown to be generically time irreversible, timereversal symmetry being modulated by opening or closing eyes [78], phase of sleep [80], and altered in a pathology-specific way in psychiatric and neurological disease [78]. Temporal irreversibility appears to be the hallmark of wakeful consciousness [81]. Indices of time asymmetry seem to be altered at various scales in brain pathology and may therefore be used as diagnostic tools [82].…”