Behavioral measurement of interhemispheric interactions during multiple episodes of falling asleep

Studies of hemispheric asymmetry in humans during sleep and falling asleep give contradictory results—there is evidence of the dominance of both the right and left hemispheres when falling asleep. Such a discrepancy in the results may be due to both the high heterogeneity of asymmetry patterns and the difficulty of ensuring homogeneous experimental conditions in neurophysiological testing. 102 healthy participants repeatedly performed a monotonous bimanual psychomotor test at home. 227 trials were selected for analysis. We extracted sequences of microsleep episodes, indicating which hand executed motor activity last before falling asleep, and calculated various complexity measures (Shannon entropy, ordinary/normalized Lempel–Ziv complexity, ordinary/conditional permutation entropy, Petrosyan dimension). After clustering the data, the extracted clusters were pairwise compared according to the indicators of the psychomotor test (total tap number, number of sleep episodes, total sleep duration, inter-tap interval). We obtained four clusters based on the complexity measures estimates. They are characterized by similar psychomotor characteristics of the research participants. The third cluster is of the greatest interest, characterized by the absence of “global” asymmetry (i.e., without a clearly expressed dominance of one of the hands), high drowsiness level and the existence of temporary hand dominances for relatively short time intervals. The results indicate against the existence of a pronounced hemispheric asymmetry when falling asleep, while at the same time testifying to the existence of short-term hand dominance episodes, possibly due to the local dynamics of functional connectivity during the wake–sleep transition. © The Author(s), under exclusive licence to EDP Sciences, Springer-Verlag GmbH Germany, part of Springer Nature 2023.