Gamma entrainment through sensory stimulation has the potential to reduce the pathology of Alzheimer’s disease in mouse models. However, clinical trials in Alzheimer’s disease (AD) patients have yielded inconsistent results, necessitating further investigation. This single-center pre-post intervention study aims to explore the influence of white matter microstructural integrity on gamma rhythm propagation from the visual cortex to AD-affected regions in 31 cognitively normal volunteers aged ≥ 65. Gamma rhythm propagation induced by optimal FLS was measured. Diffusion tensor imaging was employed to assess the integrity of white matter tracts of interest. After excluding 5 participants with a deficit in steady-state visually evoked potentials, 26 participants were included in the final analysis. In the linear regression analyses, gamma entrainment was identified as a significant predictor of gamma propagation (p < 0.001). Furthermore, the study identified white matter microstructural integrity as a significant predictor of gamma propagation by flickering light stimulation (p < 0.05), which was specific to tracts that connect occipital and temporal or frontal regions. These findings indicate that, despite robust entrainment of gamma rhythms in the visual cortex, their propagation to other regions may be impaired if the microstructural integrity of the white matter tracts connecting the visual cortex to other areas is compromised. Consequently, our findings have expanded our understanding of the prerequisites for effective gamma entrainment and suggest that future clinical trials utilizing visual stimulation for gamma entrainment should consider white matter tract microstructural integrity for candidate selection and outcome analysis.

Bilateral thermal capsulotomy with magnetic resonance-guided focused ultrasound (MRgFUS-capsulotomy) is a promising treatment option for treatment-refractory obsessive-compulsive disorder (OCD). Herein, we investi-gated the effects of bilateral thermal capsulotomy with MRgFUS on neural oscillations in treatment-refractory OCD patients. Eight patients underwent resting-state MEG with repeated recordings before and 1 and 6 months after MRgFUS-capsulotomy, and the oscillatory power and phase coherence over the entire cortical sensor area were measured. After MRgFUS-capsulotomy, the high beta band power in the fronto-central and temporal areas decreased at 1 month and remained stable for 6 months. Cortical connectivity of the high beta band gradually decreased over the entire cortical area during the following 6 months. At 1 month, improvement in anxiety and depression symptoms was significantly correlated with changes in high beta band power in both the frontotemporal and temporal areas. The treatment effect of MRgFUS-capsulotomy may be attributed to the cortical high beta band. Our results provide an advanced understanding of the neural mechanisms underlying MRgFUS-capsulotomy and other neuromodulatory interventions for treatment-refractory OCD.

BackgroundObsessive-compulsive disorder (OCD) is related to working memory impairment. Since patients with OCD have difficulty controlling their obsessive thoughts, removal of irrelevant information might be important in the pathophysiology of OCD. However, little is known about brain activity during the removal of information from working memory in patients with OCD. Our goal was to explore potential deficits in inhibitory function related to working memory processes in patients with OCD.MethodsSixteen OCD patients and 20 healthy controls (HCs) were recruited. We compared in prefrontal alpha and beta band activity derived from magnetoencephalography (MEG) between patients with OCD and HCs during multiple phases of information processing associated with working memory, especially in post-trial period of the visuospatial working memory task (the delayed matching-to-sample task), which is presumed to be related to the information removal process of working memory.ResultsPrefrontal post-trial beta power change (presumed to occur at high levels during the post-trial period) exhibited significant reductions in patients with OCD compared to HCs. In addition, the post-trial beta power change was negatively correlated with Obsessive-Compulsive Inventory-Revised total scores in patients with OCD.ConclusionsThese findings suggest that impairment in the removal of information from working memory might be a key mechanism underlying the inability of OCD patients to rid themselves of their obsessions.

With aging, optimal parameters of flickering light stimulation (FLS) for gamma entrainment may change in the eyes and brain. We investigated the optimal FLS parameters for gamma entrainment in 35 cognitively normal old adults by comparing event-related synchronization (ERS) and spectral Granger causality (sGC) of entrained gamma rhythms between different luminance intensities, colors, and flickering frequencies of FLSs. ERS entrained by 700 cd/m 2 FLS and 32 Hz or 34 Hz FLSs was stronger than that entrained by 400 cd/m 2 at Pz ( p < 0.01) and 38 Hz or 40 Hz FLSs, respectively, at both Pz ( p < 0.05) and Fz ( p < 0.01). Parieto-occipital-to-frontotemporal connectivities of gamma rhythm entrained by 700 cd/m 2 FLS and 32 Hz or 34 Hz FLSs were also stronger than those entrained by 400 cd/m 2 at Pz ( p < 0.01) and 38 Hz or 40 Hz FLSs, respectively ( p < 0.001). ERS and parieto-occipital-to-frontotemporal connectivities of entrained gamma rhythms did not show significant difference between white and red lights. Adverse effects were comparable between different parameters. In older adults, 700 cd/m 2 FLS at 32 Hz or 34 Hz can entrain a strong gamma rhythm in the whole brain with tolerable adverse effects.

Since patients with psychiatric disorders are diagnosed by the interview with clinical experts based on self-assessed symptom scales, a risk of misdiagnosis always exists due to human factors, such as the dissimulation of patients' clinical symptoms or miscommunication between patients and clinicians (Hirschefeld et al., 2003;Stensland et al., 2010). It is important for patients with psychiatric disorders to receive appropriate clinical treatments in a timely manner because a recovery rate decreases as the clinical treatment is delayed (Marín, 2016). For example, a recovery rate is approximately 60 % when patients with major depressive disorders are treated in an optimal time, but if not, the recovery rate decreases to about 17 % (Judith et al., 2017). However, misdiagnosis can cause treatment failure for patients with psychiatric disorders, leading to the aggravation of their psychiatric symptoms. Therefore, recent researchers have emphasized a necessity to develop assistant diagnosis systems to improve diagnosis accuracy. To this end, objective endophenotype biomarkers reflecting neuropathological traits of psychiatric disorders have been developed using two types of neuroimaging modalities: structural imaging tools (e.g., magnetic resonance imaging (MRI) and computed tomography (CT))

Objective: Itch is an unpleasant sensation associated with an urge to scratch and is a major health care issue associated with atopic dermatitis (AD). Contagious itch, i.e., subjective feelings of itchiness induced by watching others’ scratching behavior, is common in patients with AD. Using electroencephalography, we examined alpha (8–13 Hz) oscillations in sensorimotor areas associated with the desire to scratch in patients with AD. Methods: Thirty-six patients with AD and 34 healthy controls (HCs) participated in this study. They evaluated their itch levels after watching short videos of a model scratching or tapping parts of his body. Neural oscillations were recorded from nine electrodes, including those placed over sensorimotor areas. Time–frequency analysis was used to compare mu rhythm suppression over the sensorimotor areas in response to these videos between patients with AD and HCs. Results: The behavioral test showed that the visual stimuli induced increased feelings of itchiness in patients with AD relative to HCs under the tapping and scratching conditions. The time–frequency analysis revealed that mu rhythm suppression in response to scratching images was significantly prominent in patients with AD, but not in HCs. Conclusion: Patients with AD exhibited increased susceptibility to contagious itch. This phenomenon might be related to enhanced mu rhythm suppression in sensorimotor areas of the brain in these patients. Our findings provide new insight into the neurophysiological basis of itch sensations in patients with AD.

Neurocinematics is an emerging discipline in neuroscience, which aims to provide new filmmaking techniques by analyzing the brain activities of a group of audiences. Several neurocinematics studies attempted to track temporal changes in mental states during movie screening; however, it is still needed to develop efficient and robust electroencephalography (EEG) features for tracking brain states precisely over a long period. This study proposes a novel method for estimating emotional arousal changes in a group of individuals during movie screening by employing steady-state visual evoked potential (SSVEP), which is a widely used EEG response elicited by the presentation of periodic visual stimuli. Previous studies have reported that the emotional arousal of each individual modulates the strength of SSVEP responses. Based on this phenomenon, movie clips were superimposed on a background, eliciting an SSVEP response with a specific frequency. Two emotionally arousing movie clips were presented to six healthy male participants, while EEG signals were recorded from the occipital channels. We then investigated whether the movie scenes that elicited higher SSVEP responses coincided well with those rated as the most impressive scenes by 37 viewers in a separate experimental session. Our results showed that the SSVEP response averaged across six participants could accurately predict the overall impressiveness of each movie, evaluated with a much larger group of individuals.

Although light flickering at 40 Hz reduced Alzheimer’s disease (AD) pathologies in mice by entraining gamma waves, it failed to reduce cerebral amyloid burden in a study on six patients with AD or mild cognitive impairment. We investigated the optimal color, intensity, and frequency of the flickering light stimulus for entraining gamma waves in young adults. We compared the event-related synchronization (ERS) values of entrained gamma waves between four different light colors (white, red, green, and blue) in the first experiment and four different luminance intensities in the second experiment. In both experiments, we compared the ERS values of entrained gamma waves between 10 different flickering frequencies from 32 to 50 Hz. We also examined the severity of six adverse effects in both experiments. We compared the propagation of gamma waves in the visual cortex to other brain regions between different luminance intensities and flickering frequencies. We found that red light entrained gamma waves most effectively, followed by white light. Lights of higher luminance intensities (700 and 400 cd/m 2 ) entrained stronger gamma waves than those of lower luminance intensities (100 and 10 cd/m 2 ). Lights flickering at 34–38 Hz entrained stronger and more widely spread beyond the visual cortex than those flickering at 40–50 Hz. Light of 700 cd/m 2 resulted in more moderate-to-severe adverse effects than those of other luminance intensities. In humans, 400 cd/m 2 white light flickering at 34–38 Hz was most optimal for gamma entrainment.

Steady-state visually evoked potential based brain-computer interface (SSVEP-BCI) is one of the most researched type of BCI that uses neuronal response generated gazing at a visual stimulus flickering in distinct frequencies. However, some population called ‘SSVEP illiteracy’ who does not respond to a given flickering visual stimuli is one of the major drawbacks of the system. Up to date, researchers has attempt to overcome its drawback by developing more effective stimuli that enhances the SSVEP response itself or by introducing more sophisticated classifiers to apprehend the user’s intention. In a recent study, transcranial direct current stimulation (tDCS) on visual cortex was found to increase the SSVEP response. However, the enhanced response was found only on persons with low signal to noise ratio(SNR) rate, which can be effective only to limited number participants. In this study, we have investigated whether transcranial alternating current stimulation (tACS) enhances SSVEP responses for specific frequencies. Total twelve different flickering visual stimuli were used to induce SSVEP response, and the tACS stimulation was given with the frequency with the lowest SSVEP response. Total eight participants (4 males, 4 females, age : 26.25 ± 0.97) were recruited for this experiment, and electroencephalogram was measured from the parieto-occipital lobe where the participants’ SSVEP responses are generated. tACS was administered through a battery-driven current stimulator (Neuroelectrics starstim R32, Barcelona, Spain) where the anodal electrodes were placed at O1, Oz, O2, Pz and the cathodal electrode was placed at Cz. In this study, we found that frequency-specific tACS increases the SSVEP response of the stimulation frequency while non-stimulating frequencies had no significant differences. This study confirms that the frequency-specific tACS stimulation can effectively enhance the SSVEP responses which possibly might lead to increasing SSVEP based BCI performance and overcome SSVEP illiteracy. Keywords: steady-state visual evoked potential, transcranial alternating current stimulation, illiteracy, electroencephalogram

Sensory stimulation with 40 Hz flickering light could entrain gamma oscillations leading to decreased amyloid β burden. However, the optimum parameters of a light source to promote brain gamma activity in humans have not suggested yet. We performed the study to investigate the optimal intensity and frequency of the flickering light stimulus (FLS) in young adults.We measured electroencephalography (EEG) during the FLS presented. We compared the event-related synchronization (ERS) values of entrained gamma waves between four different luminance intensities (10, 100, 400, and 700 cd/m2 ) at 10 different flickering frequencies from 32Hz to 50Hz with an interval of 2Hz. Each frequency condition was comprised of 10 times repetition of 2-sec with inter-stimulus interval (ISI). We also examined the severity of six adverse effects in both experiments. Using the Granger causality, we compared the propagation of gamma waves in visual cortex to other brain regions between different luminance intensities and flickering frequencies.Entrained gamma activity started after the FLS onset, lasted during the FLS, and diminished after the FLS offset which was observed most highly at parietal area and steadily decreased from the parietal to the frontal area. Lights of higher luminance intensities (700cd/m2 and 400cd/m2) entrained stronger and more widely spread gamma waves than those of lower luminance intensities (100cd/m2 and 10cd/m2). Lights flickering at 34Hz ∼ 38Hz entrained stronger and more widely spread beyond visual cortex than those flickering at 40Hz ∼ 50Hz.Optimal frequency of FLS for entraining brain gamma activity in human may be different from those in animals. Higher luminance with lower gamma frequency stimulus are effective to propagate the gamma activity to the frontal area.

This study investigated deficits of spatial working memory in college students with attention-deficit/hyperactivity disorder (ADHD) traits using event-related potentials (ERPs) and the spatial 2-back task. We also computed sensory-level activity using EEG data and investigated theta and alpha neural oscillations, phase-locking values (PLV), and brain networks. Based on the scores from the Adult ADHD Self-Report Scale (ASRS) and Conners' Adult ADHD Rating Scales (CAARS), an ADHD-trait group (n = 40) and a normal control group (n = 41) were selected. Participants were required to respond to whether the presented stimulus was at the same location as that presented two trials earlier. The ADHD-trait group showed significantly slower response times than the control group in the spatial 2-back task. In terms of spectrum, the ADHD-trait group showed significantly reduced theta power than the control group. In contrast, the ADHD-trait group exhibited an increased alpha power compared to the control group with the 250-1000 ms interval after stimulus onset. In terms of the PLV, the ADHD-trait group showed significantly weaker theta phase synchrony and fewer connection numbers in frontal-occipital areas than the control group. In terms of the theta brain network, the ADHD-trait group showed a significantly lower clustering coefficient and longer characteristic path length than the control group for the theta band. The present results indicate that college students with ADHD traits have deficits in spatial working memory and that these abnormal activities in neural oscillation, functional connectivity, and the network may contribute to spatial working memory deficits.

Background: It has been frequently reported that non-negligible numbers of individuals have steady-state visual evoked potential (SSVEP) responses of low signal-to-noise-ratio (SNR) to specific stimulation frequencies, which makes detection of the SSVEP difficult especially in brain-computer interface applications. We investigated whether SSVEP can be modulated by anodal transcranial direct-current stimulation (tDCS) of the visual cortex. Methods: Each participant participated in two 20-min experiments-an actual tDCS experiment and a sham tDCS experiment-that were conducted on different days. Two representative electroencephalogram (EEG) features used for the SSVEP detection, SNR and amplitude, were tested for pre- and post-tDCS conditions to observe the effect of the anodal tDCS. Results: The EEG features were significantly enhanced by the anodal tDCS for the electrodes with low pre-tDCS SNR values, whereas the effect was not significant for electrodes with relatively higher SNR values. Conclusion: Anodal tDCS of the visual cortex may be effective in enhancing the SNR and amplitude of the SSVEP response especially for individuals with low-SNR SSVEP.

Background: Abnormalities in the 40-Hz auditory steady-state response (ASSR) of the gamma range have been reported in schizophrenia (SZ) and are regarded as important pathophysiological features. Many of the previous studies reported diminished gamma oscillations in SZ, although some studies reported increased spontaneous gamma oscillations. Furthermore, brain morphological correlates of the gamma band ASSR deficits have rarely examined. We investigated different measures of the 40-Hz ASSR and their association with brain volumes and psychological measures of SZ. Methods: The 40-Hz ASSR was measured for 80 dB click sounds (1 ms, 500-ms trains at 40-Hz, with 3050 to 3500 inter-train interval) using electroencephalography with 64 electrodes in 33 patients with SZ (male: 16, female: 17 (age range: 21-60)) and 30 healthy controls (HCs) (male: 13, female: 17 (age range: 23-64)). Four gamma oscillation measures (evoked power, spontaneous oscillations (baseline and total power), and inter-trial phase coherence (ITC)) were assessed. The source activities of the ASSR were also analyzed. Brain volumes were assessed using high-resolution magnetic resonance imaging and voxel-based morphometry and superior temporal gyrus (STG) volume measures were obtained. Results: Patients with SZ had larger total and evoked powers and higher ITC than HCs. Both groups showed significantly different association between mean evoked power and right STG volume. In HCs but not SZ, mean evoked power showed significant positive correlation with right STG volume. In addition, the two groups showed significantly different association between verbal fluency and mean evoked power. High evoked power was significantly correlated with poor verbal fluency in SZ. Conclusions: The current study found increased gamma oscillation in SZ and suggests significant involvement of the STG in gamma oscillations.

Excessive cognitive load is a one of the major cause of human error that can lead to catastrophic disasters, i.e. air traffic accidents. Therefore, maintaining proper amount of cognitive workload is important to prevent unwanted errors caused by mental burden. This study aims (1) to compare the electrophysiological differences of the brain reacting on different amount of workload, and (2) to classify different workload. Ten healthy subjects were recruited for the study. Thirty-two channels was used to record electroencephalogram (EEG) while the participants were engaging to 1- and 3-back memory task. The results showed a significant difference of P300 latency in Pz electrode, where the source activation of right insular was decreased in right insular as the cognitive workload increased. Furthermore, the workload differences was able to distinguished with 5% error using only sensor-space features.

Abstract Background The 40-Hz auditory steady-state response (ASSR) probing gamma-band oscillations may reflect N-methyl-D-aspartate receptor (NMDAR) dysfunction in patients with schizophrenia (SZ). Diminished gamma oscillations are reported in SZ, although increased spontaneous gamma oscillations are also reported. We investigated the 40-Hz ASSR and its association with brain volumes and clinical symptoms of SZ. Methods The 40-Hz ASSR was measured using electroencephalography in 33 patients with SZ and 30 healthy controls (HCs). Four gamma oscillation components (evoked power, spontaneous oscillations (baseline and total power), and inter-trial phase coherence (ITC)) were assessed. Brain volumes were assessed using high-resolution magnetic resonance imaging and voxel-based morphometry. Results Patients with SZ had larger evoked and total powers and higher ITC than HCs. In HCs, evoked power showed significant positive correlations with bilateral superior temporal gyrus (STG) volume. In SZ, the effect of positive symptoms on the path from evoked power to left STG volume was significantly moderated. In SZ with elevated positive symptoms, large evoked power predicted small left STG volume, whereas large evoked power predicted large left STG volume in those with low positive symptoms. Increased baseline power was associated with a smaller left middle frontal gyrus (MFG) volume in SZ, whereas increased ITC correlated with larger MFG volume in HCs. Discussion Our results support the NMDAR hypofunction model of SZ, and suggest significant involvement of the STG and MFG in gamma oscillations.

Electroencephalogram (EEG) spectral analysis quantifies the amount of rhythmic (or oscillatory) activity of different frequency in EEGs. Based on numerous studies that reported significant relationship between the EEG spectrum and human behavior, cognitive state, or mental illnesses, EEG spectral analysis is now accepted as one of the principal analysis methods in the field of neuroscience. Despite the tremendous amount of research related to its usefulness, EEG spectral analysis still exhibits inconsistent results among studies. This might be partly because of the various methodological decisions the researchers have to make during EEG spectral analysis. Indeed, there is no standardized analysis procedure. In this chapter, we cover some background principles of spectral analysis and introduce important issues that researchers must consider during EEG spectral analysis.

We provide an open access multimodal brain-imaging dataset of simultaneous electroencephalography (EEG) and near-infrared spectroscopy (NIRS) recordings. Twenty-six healthy participants performed three cognitive tasks: 1) n-back (0-, 2- and 3-back), 2) discrimination/selection response task (DSR) and 3) word generation (WG) tasks. The data provided includes: 1) measured data, 2) demographic data, and 3) basic analysis results. For n-back (dataset A) and DSR tasks (dataset B), event-related potential (ERP) analysis was performed, and spatiotemporal characteristics and classification results for ‘target’ versus ‘non-target’ (dataset A) and symbol ‘O’ versus symbol ‘X’ (dataset B) are provided. Time-frequency analysis was performed to show the EEG spectral power to differentiate the task-relevant activations. Spatiotemporal characteristics of hemodynamic responses are also shown. For the WG task (dataset C), the EEG spectral power and spatiotemporal characteristics of hemodynamic responses are analyzed, and the potential merit of hybrid EEG-NIRS BCIs was validated with respect to classification accuracy. We expect that the dataset provided will facilitate performance evaluation and comparison of many neuroimaging analysis techniques.

Electroencephalography (EEG) and near-infrared spectroscopy (NIRS) are non-invasive neuroimaging methods that record the electrical and metabolic activity of the brain, respectively. Hybrid EEG-NIRS brain-computer interfaces (hBCIs) that use complementary EEG and NIRS information to enhance BCI performance have recently emerged to overcome the limitations of existing unimodal BCIs, such as vulnerability to motion artifacts for EEG-BCI or low temporal resolution for NIRS-BCI. However, with respect to NIRS-BCI, in order to fully induce a task-related brain activation, a relatively long trial length (≥10 s) is selected owing to the inherent hemodynamic delay that lowers the information transfer rate (ITR; bits/min). To alleviate the ITR degradation, we propose a more practical hBCI operated by intuitive mental tasks, such as mental arithmetic (MA) and word chain (WC) tasks, performed within a short trial length (5 s). In addition, the suitability of the WC as a BCI task was assessed, which has so far rarely been used in the BCI field. In this experiment, EEG and NIRS data were simultaneously recorded while participants performed MA and WC tasks without preliminary training and remained relaxed (baseline; BL). Each task was performed for 5 s, which was a shorter time than previous hBCI studies. Subsequently, a classification was performed to discriminate MA-related or WC-related brain activations from BL-related activations. By using hBCI in the offline/pseudo-online analyses, average classification accuracies of 90.0 ± 7.1/85.5 ± 8.1% and 85.8 ± 8.6/79.5 ± 13.4% for MA vs. BL and WC vs. BL, respectively, were achieved. These were significantly higher than those of the unimodal EEG- or NIRS-BCI in most cases. Given the short trial length and improved classification accuracy, the average ITRs were improved by more than 96.6% for MA vs. BL and 87.1% for WC vs. BL, respectively, compared to those reported in previous studies. The suitability of implementing a more practical hBCI based on intuitive mental tasks without preliminary training and with a shorter trial length was validated when compared to previous studies.

Recently, in order to overcome the disadvantages of unimodal brain-imaging modalities such as low signal-to-noise ratio and vulnerability to motion artifact and to improve system performance, a multimodal imaging system (so-called hybrid system) has been emerging as an attractive alternative. In the present study, to meet the increasing demand on a hybrid brain-imaging data, we introduce open access datasets of electroencephalography (EEG) and near-infrared spectroscopy (NIRS) simultaneously measured during various cognitive tasks. The datasets contain BCI data such as motor imagery (MI)-, and mental arithmetic (MA), and word generation (WG)-related brain signals, and cognitive task data such as n-back (NB)-, and discrimination/selection response (DSR)-related brain signals. We provide the reference results of these datasets, which were validated using analysis pipelines widely used in related research fields. In particular, it was confirmed from classification analysis that a hybrid EEG-NIRS system can yield better classification accuracy than each of unimodal brain-imaging systems.

Vigilance, sometimes referred to as sustained attention, is an important type of human attention as it is closely associated with cognitive activities required in various daily-life situations. Although many researchers have investigated which brain areas control the maintenance of vigilance, findings have been inconsistent. We hypothesized that this inconsistency might be due to the use of different experimental paradigms in the various studies. We found that most of the previous studies used paradigms that included specific cognitive tasks requiring a high cognitive load, which could complicate identification of brain areas associated only with vigilance. To minimize the influence of cognitive processes other than vigilance on the analysis results, we adopted the d2-test of attention, which is a well-known neuropsychological test of attention that does not require high cognitive load, and searched for brain areas at which EEG source activities were temporally correlated with fluctuation of vigilance over a prolonged period of time. EEG experiments conducted with 31 young adults showed that left prefrontal cortex activity was significantly correlated with vigilance variation in the delta, beta1, beta2, and gamma frequency bands, but not the theta and alpha frequency bands. Our study results suggest that the left prefrontal cortex plays a key role in vigilance modulation, and can therefore be used to monitor individual vigilance changes over time or serve as a potential target of noninvasive brain stimulation.