Tracking behavioral and neural fluctuations in disorders of consciousness through actigraphy

Patients with disorders of consciousness (DoC) may suffer from fluctuations in vigilance impacting their ability to demonstrate behavioral signs of consciousness. This poses challenges for clinical diagnostic assessments, which must be repeated several times to be reliable, while the necessity for repeated neuroimaging is yet unexplored. Actigraphy may help tracking behavioral fluctuations and therefore informing on optimal time windows for clinical evaluation. This cross-sectional study quantifies the influence of these activity fluctuations on behavior- and neuroimaging-based diagnosis among DoC patients. Using data-driven rhythm decomposition of singular spectrum analysis, rhythms can be extracted without a-priori definition of periodicity. This allows the extraction of circadian (24 h) and ultradian (< 24 h) components in rest-activity. We show that DoC patients exhibit much more variability in the periods of their most prominent rhythm than controls (i.e., the proportion of ultradian to circadian rhythms is more in favor of ultradian). The explained variance of these rhythms may be an even more accurate measure, allowing to identify patients recovering from a DoC. Furthermore, a simulated analysis on retrospective data showed that using actigraphy to determine the optimal timing of clinical assessments would have reduced the number of required evaluations, and the misdiagnosis rate of a single assessment would have been reduced from 39.9% to 33.5%. Moreover, the phase of the most prominent rhythm during clinical assessment is predictive of the diagnosis. This contrasts with fluorodeoxyglucose positron emission tomography (FDG-PET), where metabolism in areas and networks related to (motor-) rhythm generation and consciousness (i.e., basal ganglia, brainstem, cerebellum, thalamus, default mode network, frontoparietal network and sensorimotor network) does not vary with the phase of the most prominent rhythm captured by actigraphy. Together, actigraphy provides individualized information on vigilance fluctuations, which can direct clinical assessments in the future.