A Wearable EEG System for Closed-Loop Neuromodulation of High-Frequency Sleep-Related Oscillations (original) (raw)
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IEEE Transactions on Biomedical Engineering, 2022
Auditory stimulation of EEG slow waves (SW) during non-rapid eye movement (NREM) sleep has shown to improve cognitive function when it is delivered at the up-phase of SW. SW enhancement is particularly desirable in subjects with low-amplitude SW such as older adults or patients suffering from neurodegeneration such as Parkinson disease (PD). However, existing algorithms to estimate the up-phase suffer from a poor phase accuracy at low EEG amplitudes and when SW frequencies are not constant. We introduce two novel algorithms for real-time EEG phase estimation on autonomous wearable devices. The algorithms were based on a phase-locked loop (PLL) and, for the first time, a phase vocoder (PV). We compared these phase tracking algorithms with a simple amplitude threshold approach. The optimized algorithms were benchmarked for phase accuracy, the capacity to estimate phase at SW amplitudes between 20 and 60 µV, and SW frequencies above 1 Hz on 324 recordings from healthy older adults and PD patients. Furthermore, the algorithms were implemented on a wearable device and the computational efficiency and the performance was evaluated on simulated sleep EEG, as well as prospectively during a recording with a PD patient. All three algorithms delivered more than 70% of the stimulation triggers during the SW up-phase. The PV showed the highest capacity on targeting low-amplitude SW and SW with frequencies above 1 Hz. The testing on real-time hardware revealed that both PV and PLL have marginal impact on microcontroller load, while the efficiency of the PV was 4% lower than the PLL. Active auditory stimulation did not influence the phase tracking. This work demonstrated that phase-accurate auditory stimulation can be delivered during home-based sleep interventions with a wearable device also in populations with low-amplitude SW.
Phase-locked loop for precisely timed acoustic stimulation during sleep
Journal of Neuroscience Methods, 2016
h i g h l i g h t s • Brain-computer interface to enhance slow-wave sleep. • Acoustic stimulation that is effective and non-invasive. • EEG power and synchronization is increased in delta band. • Accurate phase locked algorithm to track phase of EEG during slow-wave sleep. • Intervention has potential to enhance benefits of slow-wave sleep (memory, metabolism, immune system, and cardio-vascular health).
Beyond Hypnograms: Assessing Sleep Stability Using Acoustic and Electrical Stimulation
Neuromodulation : journal of the International Neuromodulation Society, 2018
Conventional polysomnographic recordings reflect brain dynamics associated with sleep architecture. We hypothesized that noninvasive tools like transcranial alternating current stimulation (tACS) and acoustic stimulation (for generating event related potentials [ERPs]) would help to predict sleep stability and provide a window to actively assess brain activity during sleep. Twelve healthy male volunteers participated in the multiple whole-night polysomnography (PSG) recording protocol. Acoustic tones (100 msec duration) were presented throughout night to evaluate ERP during sleep. Furthermore, 30 sec tACS were presented during nonrapid eye movement (NREM) and rapid eye movement (REM) sleep on subsequent two nights without disturbing the subject's sleep. For ERP analysis, event-locked artifact-free epochs from each sleep stage were averaged separately. For tACS analysis, 30 sec prestimulus and poststimulus artifact-free EEG epochs were subjected to bootstrapping-based comparison ...
Sleep, 2021
The propagating pattern of sleep slow waves (high-amplitude oscillations < 4.5 Hz) serves as a blueprint of cortical excitability and brain connectivity. Phase-locked auditory stimulation is a promising tool for the modulation of ongoing brain activity during sleep; however, its underlying mechanisms remain unknown. Here, eighteen healthy young adults were measured with high-density electroencephalography in three experimental conditions; one with no stimulation, one with up- and one with down-phase stimulation; ten participants were included in the analysis. We show that up-phase auditory stimulation on a right prefrontal area locally enhances cortical involvement and promotes traveling by increasing the propagating distance and duration of targeted small-amplitude waves. On the contrary, down-phase stimulation proves more efficient at perturbing large-amplitude waves and interferes with ongoing traveling by disengaging cortical regions and interrupting high synchronicity in the...
Alpha-wave frequency characteristics in health and insomnia during sleep
Journal of sleep research, 2016
Appearances of alpha waves in the sleep electrencephalogram indicate physiological, brief states of awakening that lie in between wakefulness and sleep. These microstates may also cause the loss in sleep quality experienced by individuals suffering from insomnia. To distinguish such pathological awakenings from physiological ones, differences in alpha-wave characteristics between transient awakening and wakefulness observed before the onset of sleep were studied. In polysomnographic datasets of sleep-healthy participants (n = 18) and patients with insomnia (n = 10), alpha waves were extracted from the relaxed, wake state before sleep onset, wake after sleep-onset periods and arousals of sleep. In these, alpha frequency and variability were determined as the median and standard deviation of inverse peak-to-peak intervals. Before sleep onset, patients with insomnia showed a decreased alpha variability compared with healthy participants (P < 0.05). After sleep onset, both groups sho...
At-home sleep monitoring using generic ear-EEG
Frontiers in Neuroscience
IntroductionA device comprising two generic earpieces with embedded dry electrodes for ear-centered electroencephalography (ear-EEG) was developed. The objective was to provide ear-EEG based sleep monitoring to a wide range of the population without tailoring the device to the individual.MethodsTo validate the device ten healthy subjects were recruited for a 12-night sleep study. The study was divided into two parts; part A comprised two nights with both ear-EEG and polysomnography (PSG), and part B comprised 10 nights using only ear-EEG. In addition to the electrophysiological measurements, subjects filled out a questionnaire after each night of sleep.ResultsThe subjects reported that the ear-EEG system was easy to use, and that the comfort was better in part B. The performance of the system was validated by comparing automatic sleep scoring based on ear-EEG with PSG-based sleep scoring performed by a professional trained sleep scorer. Cohen’s kappa was used to assess the agreement...
IEEE sensors letters, 2019
Present-day sleep research in humans is largely dependent on complex and costly laboratory setups, which require controlled supervision. As it is highly desirable to study sleep and to monitor sleep interventions in a realistic setting at home, new mobile approaches with equivalent performance to lab-based systems are needed. We present here the development and evaluation of a mobile system for sleep-biosignal monitoring and real-time intervention for ambulatory sleep research. We evaluated the system for electroencephalogram (EEG) signal quality and compared it to an established sleep EEG recording system. The real-time EEG signal processing performance was evaluated by implementing a closedloop auditory deep-sleep stimulation algorithm, and we calculated the precision of slow wave (SW) phase targeting during 93 nights. The obtained EEG signals contained similar power spectrograms and high correlations in the delta (0.98) and sigma (0.99) bands when compared to the reference system. The SW phase targeting [mean 44.6°, standard deviation (SD) 46.8°] was comparable to previously published, lab-based approaches. We have, thus, demonstrated that our device is suitable for performing unobtrusive, multinight monitoring and intervention at home.
Nature and Science of Sleep, 2020
In non-rapid eye movement (NREM) stage 3 sleep (N3), phase-locked pink noise auditory stimulation can amplify slow oscillatory activity (0.5-1 Hz). Open-loop pink noise auditory stimulation can amplify slow oscillatory and delta frequency activity (0.5-4 Hz). We assessed the ability of pink noise and other sounds to elicit delta power, slow oscillatory power, and N3 sleep. Participants and Methods: Participants (n = 8) underwent four consecutive inpatient nights in a within-participants design, starting with a habituation night. A registered polysomnographic technologist live-scored sleep stage and administered stimuli on randomized counterbalanced Enhancing and Disruptive nights, with a preceding Habituation night (night 1) and an intervening Sham night (night 3). A variety of non-phase-locked pink noise stimuli were used on Enhancing night during NREM; on Disruptive night, environmental sounds were used throughout sleep to induce frequent auditory-evoked arousals. Results: Total sleep time did not differ between conditions. Percentage of N3 was higher in the Enhancing condition, and lower in the Disruptive condition, versus Sham. Standard 0.8 Hz pink noise elicited low-frequency power more effectively than other pink noise, but was not the most effective stimulus. Both pink noise on the "Enhancing" night and sounds intended to Disrupt sleep administered on the "Disruptive" night increased momentary delta and slow-wave activity (ie, during stimulation versus the immediate pre-stimulation period). Disruptive auditory stimulation degraded sleep with frequent arousals and increased next-day vigilance lapses versus Sham despite preserved sleep duration and momentary increases in delta and slow-wave activity. Conclusion: These findings emphasize sound features of interest in ecologically valid, translational auditory intervention to increase restorative sleep. Preserving sleep continuity should be a primary consideration if auditory stimulation is used to enhance slow-wave activity.