Neural shutdown: Reduced broadband power observed during long-term isolation

Prolonged periods of social isolation and spatial confinement do not only represent an issue that needs to be faced by a few astronauts during space missions, but can affect all of us as recently shown during pandemic situations. The fundamental question, how the brain adapts to periods of sensory deprivation and re-adapts to normality, has only received little attention. During the SIRIUS-19 mission in the Institute of Biomedical Problems in Moscow operated by Russian and American and participation of the German and French space agencies, we used eyes closed and eyes open resting-state electroencephalographic (EEG) recordings to investigate how neural activity is altered during 122 days of isolation in a spatially confined, space-analogue environment. After disentangling oscillatory patterns from scale-free 1/f activity, we show that isolation leads to a reduction in broadband power and a flattening of the 1/f spectral slope. Beyond that, we observed a reduction in alpha peak frequency during isolation, but did not find strong evidence for isolation-induced changes that are of oscillatory nature. Critically, all effects reversed upon release from isolation. These findings suggest that isolation and concomitant sensory deprivation lead to a transient shutdown of the brain where the total neuronal firing rate is reduced and point towards an adaptive mechanism of the brain. It will be critical for future manned missions to further investigate whether this reduction in neuronal firing rate has any functional implications during behavioral tasks or whether this is only a phenomenon that can be observed during rest where the afferent drive is generally low.