Summary: Insomnia is a prevalent and disabling condition whose treatment is not always effective. This pilot study explores the feasibility and effects of closed‐loop auditory stimulation (CLAS) as a potential non‐invasive intervention to improve sleep, its subjective quality, and memory consolidation in patients with insomnia. A total of 27 patients with chronic insomnia underwent a crossover, sham‐controlled study with 2 nights of either CLAS or sham stimulation. Polysomnography was used to record sleep parameters, while questionnaires and a word‐pair memory task were administered to assess subjective sleep quality and memory consolidation. The initial analyses included 17 patients who completed the study, met the inclusion criteria, and received CLAS. From those, 10 (58%) received only a small number of stimuli. In the remaining seven (41%) patients with sufficient CLAS, we evaluated the acute and whole‐night effect on sleep. CLAS led to a significant immediate increase in slow oscillation (0.5–1 Hz) amplitude and activity, and reduced delta (1–4 Hz) and sigma/sleep spindle (12–15 Hz) activity during slow‐wave sleep across the whole night. All these fundamental sleep rhythms are implicated in sleep‐dependent memory consolidation. Yet, CLAS did not change sleep‐dependent memory consolidation or sleep macrostructure characteristics, number of arousals, or subjective perception of sleep quality. Results showed CLAS to be feasible in patients with insomnia. However, a high variance in the efficacy of our automated stimulation approach suggests that further research is needed to optimise stimulation protocols to better unlock potential CLAS benefits for sleep structure and subjective sleep quality in such clinical settings.

Slow-wave synchronous acoustic stimulation is a promising research and therapeutic tool. It is essential to clearly understand the principles of the synchronization methods, to know their performances and limitations, and, most importantly, to have a clear picture of the effect of stimulation on slow-wave activity (SWA). This paper covers the mentioned and currently missing parts of knowledge that are essential for the appropriate development of the method itself and future applications. Artificially streamed real sleep EEG data were used to quantitatively compare the two currently used real-time methods: the phase-locking loop (PLL) and the fixed-step stimulus in our own implementation. The fixed-step stimulation method was concluded to be more reliable and practically applicable compared to the PLL method. The sleep experiment with chronic insomnia patients in our sleep laboratory was analyzed in order to precisely characterize the effect of sound stimulation during deep sleep. We found that there is a significant phase synchronization of delta waves, which were shown to be the most sensitive metric of the effect of acoustic stimulation compared to commonly used averaged signal and power analyses. This finding may change the understanding of the effect and function of the SWA stimulation described in the literature.

Simultaneous recordings of electroencephalogram (EEG) and functional magnetic resonance imaging (fMRI) are at the forefront of technologies of interest to physicians and scientists because they combine the benefits of both modalities—better time resolution (hdEEG) and space resolution (fMRI). However, EEG measurements in the scanner contain an electromagnetic field that is induced in leads as a result of gradient switching slight head movements and vibrations, and it is corrupted by changes in the measured potential because of the Hall phenomenon. The aim of this study is to design and test a methodology for inspecting hidden EEG structures with respect to artifacts. We propose a top-down strategy to obtain additional information that is not visible in a single recording. The time-domain independent component analysis algorithm was employed to obtain independent components and spatial weights. A nonlinear dimension reduction technique t-distributed stochastic neighbor embedding was used to create low-dimensional space, which was then partitioned using the density-based spatial clustering of applications with noise (DBSCAN). The relationships between the found data structure and the used criteria were investigated. As a result, we were able to extract information from the data structure regarding electrooculographic, electrocardiographic, electromyographic and gradient artifacts. This new methodology could facilitate the identification of artifacts and their residues from simultaneous EEG in fMRI.

Functional magnetic resonance imaging (fMRI) techniques and electroencephalography (EEG) were used to investigate sleep with a focus on impaired arousal mechanisms in disorders of arousal (DOAs). With a prevalence of 2–4% in adults, DOAs are significant disorders that are currently gaining attention among physicians. The paper describes a simultaneous EEG and fMRI experiment conducted in adult individuals with DOAs ($n=10$). Both EEG and fMRI data were validated by reproducing well established EEG and fMRI associations. A method for identification of both brain functional areas and EEG rhythms associated with DOAs in shallow sleep was designed. Significant differences between patients and controls were found in delta, theta, and alpha bands during awakening epochs. General linear models of the blood-oxygen-level-dependent signal have shown the secondary visual cortex and dorsal posterior cingulate cortex to be associated with alpha spectral power fluctuations, and the precuneus with delta spectral power fluctuations, specifically in patients and not in controls. Future EEG–fMRI sleep studies should also consider subject comfort as an important aspect in the experimental design.

Sense of agency (SoA) is the subjective experience of causing and controlling one's actions. Recent studies have linked SoA to gamma-band oscillations in the right inferior parietal lobule (IPL) and suggest that it can be modulated through external interventions using neurostimulation techniques. This study aims to provide evidence for a causal role of the right IPL in SoA using multiple noninvasive brain stimulation methods (NIBS), electroencephalography (EEG), and a feedback manipulation task. In two experiments, we investigated the effect of gamma band (60 Hz) transcranial alternating current stimulation (tACS), transcranial random noise stimulation (tRNS), low-frequency (1 Hz) repetitive transcranial magnetic stimulation (rTMS), and high-frequency (10 Hz, 20 Hz) rTMS over the right IPL. As anticipated, gamma band tACS and high-frequency rTMS had distinct effects on SoA. Gamma band tACS enhanced the detection of non-self agency, while high-frequency rTMS impaired this capacity and reduced the overall SoA. EEG spectral analysis confirmed the impact of stimulation on the right IPL and highlighted the role of beta band oscillations. Using the largest subject pool to date, our study provides causal evidence for the crucial role of the right IPL in processing SoA, particularly in detecting non-self agency arising from real-time sensorimotor mismatch comparison. Our findings suggest that external stimulation affects the comparator mechanism, rather than introducing prediction errors as previously proposed, and support the view that the right IPL is more closely associated with the implicit feeling of agency rather than with higher cognitive processes.