Respiratory, cardiac, EEG, BOLD signals and functional connectivity over multiple microsleep episodes

A temporal sequence of thalamic activity unfolds at transitions in behavioral arousal state

“…Consistent with prior studies, we found an overall increase in thalamic activity and a decrease in cortical activity (Fig. 2a ), locked to arousal 50 , 51 , 68 . However, examining the time courses in each region revealed distinct temporal dynamics: after a slight rise in both regions, the thalamus exhibited a striking increase in activity before arousal.…”

“…Using the same nighttime scanning procedure and behavioral task, we recorded 97 behavioral arousals from 13 subjects (mean = 7.46 per subject, std = 5.55, min = 1, max = 21, Supplementary Table 2 ). We extracted thalamic nuclei by segmenting them anatomically in individual subject space, allowing us to identify specific nuclei within each individual 68 . To minimize signal blurring across nuclei, we used a conservative definition and analyzed only the thalamic nuclei which had a 90% probability or higher of filling at least one functional voxel in all subjects 70 , yielding nine nuclei of interest (Fig.…”

An orderly sequence of autonomic and neural events at transient arousal changes

“…S6) relative to that of the autonomic arousal (evidenced from the joint drop in PPG-amplitude and increase in HR and RV) are consistent with the sympathetic mechanism described previously (Özbay et al, 2019). A similar autonomic-fMRI relationship was observed in a recent study of microsleeps defined by periodic eye closure (Soon et al, 2021). Judging from the PPV-amplitude changes, as well as the relatively short (~10s) delay between RV and fMRI changes that was consistent with the peak delay of respiratory response function (RRF) during resting state but shorter than the ~16s delay of the RRF induced by cued deep breathing (Birn et al, 2008b;, sympathetic vasoconstriction may be the main contributor to the late, widespread signal reductions in the fMRI cascade.…”

“…In fact, the SST has previously been linked to transient (~10 seconds) modulations of brain arousal state (Liu et al, 2018(Liu et al, , 2015. Previous rsfMRI studies of spontaneous eye closure also found multiphasic signal behavior, with changes in the thalamus appearing to differ (Chang et al, 2016) and precede (Soon et al, 2021) most of cortical grey matter. Arousal transitions and their associated fMRI signal cascade may also have contributed in previous reports of spatiotemporal rsfMRI structures, such as quasi-periodic patterns (QPP) (Majeed et al, 2011) and cross-hierarchy propagations (Gu et al, 2021), both of which showed sequential fMRI co-(de)activations at different brain regions.…”

“…For example, during light sleep, autonomic arousal was found to accompany EEG K-complex activity and fMRI signal changes (Özbay et al, 2019). Microsleep episodes detected during the resting-state fMRI scans were also associated with both EEG and physiological modulations (Soon et al, 2021). These joint neuronal and autonomic changes at arousal transitions may contribute to the rsfMRI correlations with EEG and autonomic signals, which display a similar pattern of sensory/motor dominance (Chang and Glover, 2009; Goldman et al, 2002; Shmueli et al, 2007) and also appear highly dependent on brain arousal state (Falahpour et al, 2018; Özbay et al, 2019; Yuan et al, 2013).…”