Toward the better sleep: Sleep-related brain activity modulation through non-invasive brain stimulation

Abstract

Sleep is an essential part of the human lifespan, and it takes one of the third of the whole life. The development of social media and technical materials makes people keep awakened until late at night. As a result, the lack of sleep is pervasive all around the world. Brain imaging techniques were introduced to understand the mechanism of sleep, and researchers tried to improve the quality of sleep or its effect via pharmacological intervention or stimuli before or during sleep. Sleep-related memory consolidation is one of the popular research items for sleep researchers. There are studies that have investigated the effect of acoustic stimuli or electrical stimuli during the SWS. However, there have been few studies that investigated the effect of acoustic stimulation during sleep spindle activity. In this study, we examined the neurophysiological effect of acoustic stimulation after sleep spindle activity. After detecting the sleep spindle, we delivered pink noise and surmised that acoustic stimulation after sleep spindle detection might preserve delta activity during ongoing sleep. To accomplish such a targeted-manner of stimuli delivery, we built a real-time closed-loop feedback system for sleep EEG. With a successful introduction of such a system, we observed suppression of the sleep spindle activity during the acoustic stimulation period and evoked SW and theta band activity immediately after tone onset. Previous studies were arguing the role of sleep spindle as sleep protection from sensory information processing. When we consider normal sleep without any acoustic feedback after spindle detection, it is assumed that acoustic stimulation temporarily stabilizes and deepens ongoing sleep. Furthermore, we observed sleep-related procedural memory consolidation improvement after the nap with spindle-targeted acoustic stimulation. Spindle density does not affect by acoustic stimuli. Therefore such improvement may result in spindle-slow oscillation pair modulated by pink noise stimulation after spindle detection. In the last chapter, we proposed future directions for sleep research with closed-loop feedback systems, which provide some insight into closed-loop feedback systems.