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Nearly half the nation’s military members report less than five hours of sleep per night, an alarming statistic that highlights the need for effective fatigue countermeasures to ensure the well-being and operational efficiency of the armed forces. It’s more than simply spending more time in bed; emerging approaches focus on improving the quality of sleep.

Researchers at the ����ֱ�� Applied Physics Laboratory (APL) in Laurel, Maryland, are developing a smart tool that employs a brain-like artificial neural network to monitor an individual’s sleep in real time. It also delivers stimuli, like sounds or changes in temperature, at precisely the optimal moments to enhance the quality of the user’s sleep.

This groundbreaking effort, one of many at APL focused on sleep deprivation, aims to optimize the stages of sleep that are crucial for overall health and cognitive prowess.

Auditory Stimulation and Temperature Change

Recent research has shed light on the role of EEG “slow waves” — a hallmark of deep non-rapid-eye-movement sleep — in facilitating restorative sleep. Scientists have discovered that auditory stimuli, meticulously timed to synchronize with the brain’s natural rhythms, can evoke these slow waves, boosting their activity by up to 20%. (This phenomenon has been linked to the activation of the glymphatic system, the brain’s waste-clearance mechanism.)

However, effectively synchronizing external stimuli requires precise timing, said APL’s Will Coon, a sleep scientist and neural signals engineer who serves as principal investigator for this effort.

“The effectiveness of this phase-locked stimulation relies on precisely matching the auditory cues with the brain’s internal slow-wave rhythms, and only during certain stages of sleep,” Coon explained. “If the timing isn’t just right, even if the stimuli are limited to the non-rapid-eye-movement sleep stage, their impact won’t be realized.”

This challenge highlights the need for automated systems, Coon said, that can spot slow waves, study how they behave and figure out the perfect times to play those sounds in real time, often within half a second from spotting the slow wave.

Using advanced algorithms designed for analyzing sleep patterns, along with a small device similar in size to an Apple Watch, Coon and his team can pinpoint the exact sleep stage an individual is experiencing at any time, and know to look for slow waves only when the sleeper is in the right sleep stage. The system can then detect slow waves from ongoing brain activity, predict when subsequent slow waves should occur, and provide carefully timed sound cues to enhance slow-wave activity and improve brain functions associated with the restorative aspects of sleep.

Even more exciting, Coon said, is where the team is going next: a groundbreaking method pioneered at APL that could enhance the duration of this restorative sleep stage using changes in temperature. Prior research has shown that properly timed cooling during sleep can increase slow-wave activity. However, without knowing the sleeper’s current sleep stage, timing the cooling is guesswork at best. APL’s real-time sleep stage decoder overcomes this limitation by keeping temperature changes tightly aligned with the sleeper’s own natural sleep cycle, which transitions through various sleep stages multiple times each night, typically every 80 to 120 minutes.

“Controlling the change in temperature of the sleeper can have an even bigger effect than using sound alone, even when only a delay timer is used instead of the sleeper’s own sleep-cycle patterns,” Coon said. “We’re talking about less than half a degree Celsius, so not much of a swing. Controlling the cooling with our system has the potential to increase this effect even more. If you can get more slow-wave sleep or more deep sleep, you might be able to get a full night’s rest in less time.”

Top of Mind

The team has also developed a custom sensor extension designed to measure brain activity at the vertex — the top of the head. While frontal sensors are sufficient for sleep staging and slow-wave stimulation, certain cognitive processes tied to learning, memory and cognitive function occur near the central sulcus, a prominent groove on the surface of the brain. The potential to measure these processes opens doors for targeted memory enhancement through properly timed stimulus delivery.

The system’s structure is versatile because it can work with different types of stimuli, such as sounds, temperature, electrical impulses, visuals or physical sensations. It’s compact and easily attaches to a headband.

“One of the big barriers for people that use sleep devices is the need to put something on your head,” explained Griffin Milsap, a senior neuroscientist at APL and co-investigator on the project. “There are a lot of ways to track sleep these days, including accelerometers on your wrist and heart rate monitors that give you some idea of what sleep is doing. But if you really want to see what’s happening in sleep, you do need something on your head, and the smaller we can make that device, the better.”

Enhancing Sleep Automatically

The team is tackling the limitations of slow-wave stimulation methods that rely on rudimentary algorithms or human experts to recognize sleep states.

“Our device takes the burden off human intervention, and maximizes accuracy by introducing an automated algorithm that can distinguish sleep stages through the analysis of EEG brain waves,” Milsap explained. “This ensures that the delivery of sounds that are timed to align perfectly with the brain’s natural slow-wave rhythms occur precisely during the right sleep stages to enhance slow-wave activity.”

Coupling the sleep stage decoder with slow-wave detection constitutes a holistic solution capable of independently initiating slow-wave stimulation, he added.

Sleep’s Transformative Possibilities

While the team’s main goal is to make an affordable and highly effective sleep aid, its device could also unlock a range of transformative possibilities, including treating traumatic brain injuries and enhancing the cognitive abilities of warfighters, according to Coon.

“By harnessing the power to stimulate slow waves that may, in turn, rejuvenate the glymphatic system, we open doors to restoring vital brain functions damaged by injury or the onset of neurodegenerative diseases such as Alzheimer’s,” he said. “This technology’s potential in memory modulation, particularly in the context of conditions like post-traumatic stress disorder, hints at a future when we can intervene in memory consolidation processes to prevent the enduring effects of trauma.”

APL’s sleep engineering studies — funded over the last three years by Independent Research and Development grants from APL’s Research and Exploratory Development Department and Global Health Mission Area — are paving the way for large-scale efforts to deepen understanding of the underlying physiology and enabling the deployment of systems in the field.

“The prospect of reducing the required sleep duration by warfighters could be a game-changer in our relentless pursuit of enhancing their capabilities,” Coon said.

​”We are right on the cusp of what I think is going to be a Cambrian explosion of new ways to interact with the sleeping brain,” he added. “It’s been understudied for most of human history. We only started to formalize definitions of human sleep stages about 75 years ago, and now we’re finding all kinds of new ways to stimulate and enhance sleep to improve health and performance — we’ve moved from measuring to controlling, in a sense. Technology has caught up.”​