Tailoring Human Sleep: selective alteration through Brainstem Arousal Circuit Stimulation

Abstract

AbstractBrainstem nuclei, such as the pedunculopontine nucleus, send activating projections to cortex, modulating states of sleep, wakefulness and arousal levels. Surgical modulation of subcortical activity using deep brain stimulation (DBS) is utilised in the management of pain and movement disorders. DBS of brainstem arousal circuits in a state-dependent manner could offer an attractive alternative in severe pharmacoresistant cases of hypersomnia and in disorders of consciousness, where behavioural activation is desired.We wanted to investigate if we can selectively induce wakefulness and/or alter sleep state through DBS of the PPN region (PPNR). To this end, we used the opportunity of implanted PPNR electrodes in stimulation-naïve patients with multiple systems atrophy. PPNR activity was recorded during both slow wave sleep (SWS) and quiet wakefulness with simultaneous cortical EEG, in order to identify differences in brainstem oscillatory patterns during different states of excitability. PPNR DBS in two gamma frequency protocols (40Hz and 100Hz) was delivered during SWS of the same sleep stage and with comparable pre-trial levels of slow wave activity.Additionally, SHAM trials were used as a control where no stimulation was applied. We examined changes in cortical oscillatory power, changes in functional connectivity (coherence and causality) from pre- to post-stimulation and phase-locking of cortical oscillations with DBS frequencies and their sub-harmonics during stimulation. We also evaluated connectivity changes induced by DBS and corresponding differences in circuit dynamics between SWS and wakefulness.Beta and gamma PPNR oscillatory power increased when wake was compared to sleep. We saw clear PPNR power modulation by the phase of EEG slow wave, with significant increase in gamma compared to beta power during the ‘excitable’ part of the slow-wave cycle. Gamma PPNR DBS induced transitions to wakefulness and REM, while it truncated sleep time compared to baseline. The 40Hz stimulation protocol was more efficient in reducing slow wave activity and increasing cortical beta power, compared to PPNR DBS at 100Hz. Furthermore, intrinsic cortical rhythms phase-locked with 40 Hz PPNR DBS to a significantly higher degree compared to the 100Hz protocol, with regional differences in phase-locking, suggesting a complex biological phenomenon. Finally, functional connectivity changes induced by PPNR DBS were consistent with differences in circuit dynamics between SWS and wakefulness. Overall, these results highlight the possibility of using DBS of brainstem arousal circuits to promote arousal and wakefulness, which opens new perspectives for using closed-loop approaches to modulate vigilance states in humans for therapeutic benefit.