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Abstract :
[en] Living organisms are characterized by a high level of complexity, and their biological signals often exhibit long-term correlated fluctuations that are best described by fractal scaling indices over a wide range of time scales. Sleep is a well-suited state to study these fluctuations, being organized into structured oscillatory patterns. With ageing and in neurodegenerative diseases, sleep functions are degraded, and fractality was reported to be altered. However, the interplay between ageing and sleep on fractal regulation of brain activity remains unclear.
In this study, we investigated how age affects fractal regulation of both wake and sleep electroencephalography (EEG) signals acquired during one night of sleep in the lab in 454 young and older individuals (N=360, 18-32 y; N=94, 59-82 y). Fractal coefficients, at short or long timescales, were obtained with Detrended Fluctuations Analysis (DFA).
Our first analysis suggested that DFA coefficients are larger in sleep than in wake, which is coherent with the literature. Further analysis revealed a statistically significant age effect (p<0.001) on the long timescale-DFA coefficient across all sleep stages with older individuals showing reduced coefficient compared to younger individuals. Furthermore, in deeper sleep stages (N2, N3), this effect is stronger than in other stages.
These findings suggest an age-related complexity loss in brain signals, notably in slow wave sleep. Given the importance of sleep for different cognitive processes such as memory consolidation, decision-making and emotional processing, our future work will evaluate how fractal regulation of brain activity relates to cognitive status in both healthy and pathological ageing.
