# Time irreversibility of resting brain activity in the healthy brain and pathology

## TL;DR

This study investigates the time-reversal symmetry of resting brain activity using EEG, revealing that healthy brains exhibit time-irreversibility which is reduced in pathological conditions, with implications for understanding brain dynamics.

## Contribution

It demonstrates that resting brain activity is generally time-irreversible and shows pathology-specific reductions in time asymmetry, advancing understanding of brain dynamics in health and disease.

## Key findings

- Resting brain activity is time-irreversible at long time scales.
- Pathology reduces the time asymmetry of brain activity.
- Experimental conditions modulate the degree of time irreversibility.

## Abstract

Characterising brain activity at rest is of paramount importance to our understanding both of general principles of brain functioning and of the way brain dynamics is affected in the presence of neurological or psychiatric pathologies. We measured the time-reversal symmetry of spontaneous electroencephalographic brain activity recorded from three groups of patients and their respective control group under two experimental conditions (eyes open and closed). We evaluated differences in time irreversibility in terms of possible underlying physical generating mechanisms. The results showed that resting brain activity is generically time-irreversible at sufficiently long time scales, and that brain pathology is generally associated with a reduction in time-asymmetry, albeit with pathology-specific patterns. The significance of these results and their possible dynamical aetiology are discussed. Some implications of the differential modulation of time asymmetry by pathology and experimental condition are examined.