The closed-loop auditory stimulation technology developed for this study precisely times sounds to specific phases of brain wave oscillations, such as the waxing and waning phases. The sounds were administered at frequencies configured to either six or ten stimuli per second. This study marks the first instance of such stimulation being applied during the REM sleep period, a stage where brain activity resembles wakefulness while the body remains immobilized.
Dr. Valeria Jaramillo, Swiss National Science Foundation postdoctoral fellow at the Surrey Sleep Research Centre and School of Psychology at the University of Surrey, emphasizes the significance of brain oscillations in cognitive functions. According to Dr. Jaramillo, “Brain oscillations assist in the working of the brain and how it learns and retains information. Brain oscillations during REM sleep have been implicated in memory functions – however, their exact role remains largely unclear. In dementia, brain activity during REM sleep becomes slower, XXYPLACEHOLDER1YXX which is associated with a reduction in the ability to remember certain life events and retain information.”
The potential to stimulate brain waves with sound to increase their frequency offers a promising way to better understand the function of brain oscillations during REM sleep and to enhance this critical sleep stage in dementia patients. To investigate this further, the research team recruited 18 participants for overnight monitoring at the Surrey Sleep Research Centre. Throughout the night, their sleep was continuously monitored using electrodes placed on their scalps to record brain oscillations in real time. This method allowed the precise administration of auditory stimuli at targeted points within the oscillation cycles without waking the participants.
The research demonstrated that auditory stimuli could manipulate brain oscillations to become either faster or slower, depending on the phase of the cycle targeted. Professor Derk-Jan Dijk, Director of the Surrey Sleep Research Centre and UK Dementia Research Institute Group Leader, highlighted the potential implications of these findings, stating, “This could pave the way XXYPLACEHOLDER2YXX for a new approach on how to treat patients with dementia, as the technique is non-invasive and undertaken whilst they are asleep, lessening the disruption to their lives and enabling us to be more targeted in our approach.”
Dr. Ines Violante, Senior Lecturer in Psychological Neuroscience at the University of Surrey and senior author of the publication, noted the therapeutic promise of using sound stimulation to alter brain oscillations during sleep. “Using sound stimulation to change brain oscillations whilst a person sleeps shows therapeutic promise. There is currently no cure for dementia, only medication that can slow down disease progression or temporarily help a person with their symptoms, so it is important that we think innovatively to develop new treatment options. Sound stimulation, which is a non-invasive inexpensive technique, has the potential to do just this,” Dr. Violante remarked.
The study, titled “Closed-loop auditory stimulation targeting alpha and theta oscillations during REM sleep induces phase-dependent power and frequency changes,” sought to understand the modulation of alpha and theta XXYPLACEHOLDER3YXX oscillations—brain wave patterns that characterize the waking human electroencephalogram (EEG). These oscillations also occur during REM sleep, but their function in this context has remained elusive until now. The research involved recording high-density EEG data during an extended overnight sleep period in 18 healthy young adults. Auditory stimulation was administered using a pattern of alternating 6-second ON and 6-second OFF windows during both phasic and tonic REM sleep. During the ON windows, the auditory stimuli were phase-locked to four orthogonal phases of ongoing alpha or theta oscillations detected in a frontal electrode.
The results were revealing. The phases of ongoing alpha and theta oscillations were targeted with high precision during REM sleep, leading to phase-dependent changes in power and frequency at the target location. Specific effects were observed for the alpha trough and rising phases, inducing speeding up and slowing down, respectively, and for the theta trough conditions. Interestingly, CLAS-induced phase-dependent changes were noted across both phasic and tonic REM sleep substages, although auditory evoked potentials were XXYPLACEHOLDER4YXX significantly reduced in phasic compared to tonic REM sleep.
The study concludes that faster REM sleep rhythms can be modulated by closed-loop auditory stimulation in a phase-dependent manner. This discovery opens new research avenues to investigate the role of REM sleep oscillations in cognitive functions and suggests potential therapeutic interventions for improving brain activity during sleep in patients with dementia. As the research presents a novel, non-invasive, and cost-effective method, it highlights the promise of closed-loop auditory stimulation as a transformative tool in cognitive neuroscience and dementia treatment.