Evaluation of SmartSleep Technology for Improving the Efficiency and Restorative Quality of Sleep in Healthy Adults in Order to Mitigate Cognitive Performance Deficits Due to Sleep Restriction and Emergency Awakenings

[Ed. note May 2020: Report submitted by TRISH to Task Book in March 2020; covers reporting as of November 2019.]

Astronauts must maintain a high level of cognitive performance capability in spaceflight, which depends on their acquiring adequate daily sleep quantity and sleep quality while in space, and on their ability to respond quickly and effectively to emergency events that can occur when they are asleep. Studies have found reduced sleep duration and reduced sleep quality in spaceflight. Earth-based studies have shown that this degree of sleep loss can adversely affect waking cognitive performance. Sleep medications have been used in spaceflight to improve sleep quality and sleep duration, yet these medications compromise the cognitive performance capability of astronauts when an emergency awakening requires them to function effectively. Thus, there is a need for a technology that can improve sleep quality in space and biologically maximize the performance benefits of limited sleep duration, without unduly affecting the ability of astronauts to awaken abruptly due to an inflight emergency. Studies have found that acoustic enhancement of electroencephalogram (EEG) slow waves during sleep can increase subsequent cognitive performance. This approach to improving sleep quality and the cognitive benefits of sleep is now available as "SmartSleep," a new technology that enhances slow waves using inaudible acoustic stimulation during sleep. SmartSleep consists of a headband worn during sleep and a sleep app.

The project will utilize this technology in a controlled, double-blind, laboratory study of non-invasive brain stimulation in healthy normal astronaut-like adults, to evaluate whether slow wave sleep enhancement via the SmartSleep stimulus algorithms could benefit cognitive performance during sleep restriction, and/or decrease the severity and duration of sleep inertia after abrupt awakening from sleep. The project has three objectives:

Objective 1: Evaluate whether slow wave sleep enhancement via the SmartSleep stimulus algorithms benefits daytime cognitive performance during a period of chronic sleep restriction as commonly observed during spaceflight (Deliverable 1). We will assess cognitive performance with the Cognition test battery (developed for NASA by our laboratory) across a range of cognitive domains and across a number of high fidelity spatial cognition tasks and spaceflight-relevant operational tasks including Robotic On-Board Trainer (ROBoT); Six Degrees of Freedom Docking Simulator (6DF); and Lunar Landing Simulation.

Objective 2: Investigate whether SmartSleep slow-wave enhancement decreases performance decrements induced by sleep inertia after an emergent awakening (Deliverable 2).

Objective 3: Identify the best modality of SmartSleep acoustic stimulation in terms of slow-wave enhancement and cognitive performance among three different stimulation techniques: Continuous Fixed Interval (1 Hz, inter-tone interval stimulation), Block (5 seconds on versus 5 seconds off), and In-Phase Adjustable (constant stimulation with tones to be delivered during each upstate of the slow wave) [Deliverable 3].

The project objectives will be achieved through the following specific aims:

Specific Aim 1: Determine whether EEG slow-wave sleep can be enhanced via closed-loop auditory stimulation of EEG slow waves in healthy adult subjects using SmartSleep Headband technology, when sleep is restricted in duration to 5h per night over four consecutive nights.

Specific Aim 2: Determine whether post-sleep cognitive performance functions sensitive to sleep restriction can be enhanced when SmartSleep closed-loop auditory stimulation is used on sleep-restricted nights relative to a sham SmartSleep control condition.

Specific Aim 3: Identify the acoustic stimulation modality with maximal benefits for EEG slow-wave enhancement and daytime cognitive performance, when sleep is restricted in duration to 5h per night over 4 consecutive nights.

Specific Aim 4: Investigate systematic effects of consecutive nights of sleep restriction on EEG slow-wave enhancement, daytime cognitive performance, emotion recognition, and emotional valence, and stress reactivity.

Specific Aim 5: Assess potential adverse effects of SmartSleep utilization during sleep restriction, especially related to sleep inertia after emergent awakening. During the first year of the project, the project met the proposed timeline for data collection, with n=6 of a planned total n=12 participants completing the 7-day laboratory protocol (i.e., n=42 subject nights completed in the laboratory, out of a projected total of 84 nights).

A key finding from the first year was that participants wore the SmartSleep headband device without discomfort or adverse events and that the participants did not report hearing audio tones during wakefulness or sleep. Participants also successfully completed all neurocognitive and spaceflight-relevant operational tasks. Moreover, optimization of the SmartSleep algorithm progressed by correcting initial technology issues, which were identified through regular data quality control checks conducted by the project team. The findings and progress made during the first year of the project will facilitate high quality data collection in the second year of the project.

The research plan for the second year of the project includes the recruitment, enrollment, and completion of 7-day laboratory study protocol for the remaining n=6 participants. Statistical analysis of study findings will be conducted after completion of data collection according to the study design. Furthermore, study findings will be prepared for publication in a peer-reviewed journal.