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Cognitive control allows to flexibly guide behaviour in a complex and ever-changing environment. It is supported by theta band (4-7 Hz) neural oscillations that coordinate distant neural populations. However, little is known about the precise neural mechanisms permitting such flexible control. Most research has focused on theta amplitude, showing that it increases when control is needed, but a second essential aspect of theta oscillations, their peak frequency, has mostly been overlooked. Here, using computational modelling and behavioural and electrophysiological recordings, in three independent datasets, we show that theta oscillations adaptively shift towards optimal frequency depending on task demands. We provide evidence that theta frequency balances reliable set-up of task representation and gating of task-relevant sensory and motor information and that this frequency shift predicts behavioural performance. Our study presents a mechanism supporting flexible control and calls for a reevaluation of the mechanistic role of theta oscillations in adaptive behaviour. Senoussi et al. present modelling, behavioural and neural evidence that frontal theta oscillations (4-7 Hz) shift their peak frequency in response to task demands to support flexible task implementation.

We studied the effect of optical stimulation (10 Hz) on the effectiveness of mnestic activity in the n-back task in healthy subjects (n=32). EEG was recorded at all stages of the examination. The absolute values of the spectral power of the 10 Hz frequency (μV2) of the alpha range were calculated. According to the results of the test without optical stimulation, the examinees were divided into groups with high (group 1) and low (group 2) task performance. In the initial state, the spectral power of 10 Hz was significantly higher in group 1 subjects. Under conditions of screen flickering, the results became poorer in group 1 and better in group 2 in comparison with the results under normal conditions. These changes were accompanied by an increase in the spectral power of 10 Hz only in group 2 subjects. These findings can provide the basis for the development of practical recommendations for improving the mnestic functions in patients with consideration for the individual characteristics of their initial EEG.

Background Cue-reactivity is the array of responses that smokers exhibit when exposed to conditioned and contextual stimuli previously associated to substance use. The difficulty to experimentally recreate the complexity of smokers’ spatial experience and context requires more ecological models. Virtual reality (VR) creates a state of immersion close to reality allowing controlled assessments of behavioral responses. To date, no studies investigated brain activation associated to smoking cue-reactivity in VR using electroencephalography (EEG). Aims To investigate whether a VR cue-reactivity paradigm (a) may increase smoking craving, (b) is feasible with EEG recording, and (c) induces craving levels associated to EEG desynchronization. Methods Smokers (N = 20) and non-smokers (N = 20) were exposed to neutral and smoking-related VR scenarios, without and with smoking conditioned stimuli, respectively. EEG was recorded from occipital and parietal leads throughout the sessions to assess alpha band desynchronization. Smoking and food craving and presence visual analogue scales (VAS) were assessed during the session. Results To be smoker, but not non-smoker, significantly influenced smoking craving VAS induced by smoking cue VR but not by neutral VR. No significant food craving changes was observed during the VR sessions. The new finding was that EEG alpha band power in posterior leads was significantly increased by the smoking context scenario only in smokers, and that the degree of smoking (i.e., heavy vs. light) was significantly associated to this neurophysiological measure. Conclusions This study demonstrated, for the first time, the feasibility of EEG recording in a VR setting, suggesting that EEG desynchronization may be a neurophysiological marker of smoking cue-reactivity.

Our recent study demonstrated that prefrontal transcranial photobiomodulation (tPBM) with 1064-nm laser enables significant changes in EEG rhythms, but these changes might result from the laser-induced heat rather than tPBM. This study hypothesized that tPBM-induced and heat-induced alterations in EEG power topography were significantly distinct. We performed two sets of measurements from two separate groups of healthy humans under tPBM (n = 46) and thermal stimulation (thermo_stim; n = 11) conditions. Each group participated in the study twice under true and respective sham stimulation with concurrent recordings of 64-channel EEG before, during, and after 8-min tPBM at 1064 nm or thermo_stim with temperature of 33–41 °C, respectively. After data preprocessing, EEG power spectral densities (PSD) per channel per subject were quantified and normalized by respective baseline PSD to remove the power-law effect. At the group level for each group, percent changes of EEG powers per channel were statistically compared between (1) tPBM vs light-stimulation sham, (2) thermo_stim vs heat-stimulation sham, and (3) tPBM vs thermo_stim after sham exclusion at five frequency bands using the non-parametric permutation tests. By performing the false discovery rate correction for multi-channel comparisons, we showed by EEG power change topographies that (1) tPBM significantly increased EEG alpha and beta powers, (2) the thermal stimulation created opposite effects on EEG power topographic patterns, and (3) tPBM and thermal stimulations induced significantly different topographies of changes in EEG alpha and beta power. Overall, this study provided evidence to support our hypothesis, showing that the laser-induced heat on the human forehead is not a mechanistic source causing increases in EEG power during and after tPBM.

What is your brain doing while your mind is wandering? This study used a within-subjects experience-sampling design to test whether episodes of mind-wandering during a demanding cognitive task are associated with increases in EEG alpha power. Alpha refers to cyclic oscillations in EEG activity at 8-12 Hz, and has been previously correlated with internally rather than externally directed cognition. Participants completed a speeded performance task with more than 800 trials while EEG was recorded. Intermittent experience-sampling probes asked participants to indicate whether their mind was wandering or on-task. Participants reported mind-wandering in response to approximately half of the probes. EEG alpha power was significantly higher preceding probes to which participants reported mind-wandering, compared with probes to which participants reported being on task. These findings imply that dynamic changes in alpha power may prove a valuable tool in studying momentary fluctuations in mind-wandering.

The objective of the study is to analyze electroencephalograms (EEGs) of patients with schizophrenia using power spectral density. The proposed method measures various absolute powers that are related to the amount of information contained in the frequency components. 57 schizophrenia subjects and 24 normal subjects were included the study. EEG recordings were obtained under resting, hyperventilation and post-hyperventilation with eyes closed conditions. The absolute total power for 10 s epochs of EEGs was calculated using Welch’s method. The delta, theta, alpha, and beta bands were extracted from EEGs using a finite impulse response band pass filter and the power was determined. The differences in the absolute powers of the beta band and alpha bands were significant between the two groups (p

Mindfulness meditation (MM) and EEG-alpha neurofeedback (NFB) have both been shown to improve attentional performance and increase full 8–12-Hz EEG alpha amplitude, but no studies have compared MM and NFB on their effects for modulating EEG alpha or attentional control. Sixty-one university students were randomized to a 15-min single-session MM (n = 24), NFB (n = 17), or sham-NFB (SHAM; n = 20) intervention and were compared on EEG alpha full and sub-band amplitudes during completion of a single 15-min session of either intervention across 5 successive 3-min epochs, as well as during performance of the Stroop test. MM and NFB participants demonstrated higher global full-band alpha amplitude when compared with SHAM participants during the final intervention epoch, whereas no group differences were observed for sub-band amplitudes. In the absence of group differences in behavioral performance, MM participants exhibited a lower ERD of the upper alpha-band within frontal cortex 200–400 ms post-stimulus on the Stroop task, an effect that correlated with upper alpha amplitudes demonstrated during the intervention. Future research directions are discussed.

Previous studies on insight problem solving using Chinese logogriphs as insight problems only investigated the time- and phase-locked changes of electrocortical responses triggered by Chinese logogriphs, but did not focus on what kind of brain state facilitates individuals to solve insight problems. To investigate this, we focused on participants' alpha activities (8-12 Hz) that closely correlates with insight problem solving and defocused attention while they were solving Chinese logogriphs. Results indicated that in the time window of 800-1400 ms after the presentation of target logogriphs, alpha power over parieto-central electrodes decreased relative to the reference interval in both the successful and unsuccessful logogriphs solving conditions. However, alpha power increased at parieto-occipital electrode sites in successful conditions compared with that in unsuccessful condition. The decrease in alpha activity in both conditions may reflect the cognitive demands in solving the target logogriphs. Furthermore, difference in alpha power between the successful and unsuccessful conditions at parieto-occipital electrode sites is associated with the process of heuristic information. Alpha synchronization observed in the successful condition compared to the unsuccessful condition might reflect a state of defocused attention that facilitates insight problem solving.

We investigated the temporospatial dynamics of the power of the phase-linked component and the total power of EEG alpha oscillations on presentation of an illusory outline (Kanizsa square) and a control nonillusory image to 16 healthy adult subjects. Alpha oscillations were identified using wavelets; statistical assessments of the dynamics of alpha power were studied by analysis of variance, along with a new nonparametric multifactorial analysis method. Presentation of visual stimuli was found to be accompanied by early increases in the total power of alpha oscillations, which were more marked on perception of the illusory outline as compared with the control stimulus (the “illusion effect”). This early short phase of the alpha response arose mainly because of the phase-linked component, and was followed by a longer-lasting phase of depression of the total power of alpha oscillations (“alpha rhythm blockade”), which was nonspecific in relation to the type of stimulus. Both phases of the alpha response were most marked in the parietal-temporal-occipital areas of the right hemisphere. We propose that the first increase in alpha oscillations reflects modulation of the activity of neuron ensembles involved in processing the overall patterns, while alpha rhythm blockade is associated with orientation processes.

This article reports on a study to identify electroencephalography (EEG) signals with potential to provide new BCI channels through mental motor imagery (MMI). Leg motion was assessed to see if left and right leg MMI could be discriminated in the EEG. The study also explored simultaneous observation of leg movement as a means to enhance MMI evoked EEG signals. The results demonstrate that MMI of the left and right leg produce a contralateral preponderance of EEG alpha band desynchronization, which can be spatially discriminated. This suggests that lower extremity MMI could provide signals for additional BCI channels. The study also shows that movement imitation enhances alpha band desynchronization during MMI, and might provide a useful aid in the identification and training of BCI signals.

In a task switching design, we investigated the question whether long-range theta coupling primarily reflects top-down control processes. Switch and stay trials did not differ with respect to memory load or global working memory (WM) demands. The results revealed significantly stronger theta coupling (in a range of 4-7 Hz) between prefrontal and posterior regions during switch as compared to stay trials. Power differences, reflecting more local effects, were largest in the upper alpha band (10-13 Hz) and over posterior brain areas, possibly reflecting long-term memory activation. The conclusion of the present study is that long-range coherent oscillatory activity in the theta band reflects top-down activation rather than global WM functions.

Skin resistance and EEG alpha were recorded concurrently during alpha biofeedback, in which the participant attempted to control alpha, and during skin resistance biofeedback, in which the participant attempted to control skin resistance. Alpha production changed significantly (p less than .001) during alpha biofeedback, indicating successful self-regulation of alpha, but did not change significantly during skin resistance biofeedback. Similarly, skin resistance changed significantly (p less than .001) during skin resistance biofeedback but did not change significantly during alpha biofeedback. The results show independent control of alpha and skin resistance, and may reflect independent self-regulation of cognitive and somatic tension-relaxation systems.

The problem of defining EEG alpha activity, and of detecting and measuring it, is outlined. Some advantages of a threshold method are presented and compared with an amplitude-integration method. Characteristics of percent-time scoring, based upon observable alpha spindles in the waking EEG, are discussed. A probability distribution of percent-time alpha as a function of detection threshold is derived and compared with empirical data.

The effect of the experimenter’s expectations about experimental outcomes on two physiological variables (EMG and EEG) were investigated in an experiment involving a tendon tap stimulus used to elicit a phasic stretch reflex. Experimenter’s and subject’s perceived locus of control scores were incorporated into the design to test their relevance as a mediating variable. Immediately after the presentation of the tendon tap stimulus, subject’s EEG alpha measures were found to be more biased in the direction of the experimenter’s expectations when experimenters and subjects were similar in their scores on the perceived locus of control scale. Biasing effects on EEG alpha measures in the direction of experimenter’s expectations were found early in the experimental session where subjects or their experimenters scored as internally controlled. The EMG measures increased or decreased in the direction of the experimenter’s expectations when subjects were internally controlled but there was a reversal of the direction of the experimenter’s expectations with subjects who scored as externally controlled so that no significant experimenter expectancy effect was observed.

Twenty-four human volunteers were given one 30-min EEG alpha biofeedback training session within an active placebo setting. Ten dependent measures computed from serial 3-min period distributions showed no difference between contingent and yoke conditions or between 9-11 and 8-13 Hz feedback. Most subjects showed entrainment of the alpha rhythm toward a stable frequency over trials. Five additional subjects given five daily 30-min sessions of 9.5-10.5 Hz feedback showed a repetition of this same effect. Over a period of 4 months, one grand mal epileptic gradually entrained a bimodal period distribution toward a unimodal one centered at 10 Hz. This effect was paralleled by a significant drop in seizure rate. These results were interpreted in terms of electrophysiological homeostasis.

Current controversies concerning outcomes of EEG alpha feedback training are at least in part due to methodological differences among different studies. The aim of this paper is to provide future and present researchers in this field with an analysis of methods used in most of the studies published from 1968 to 1976, and to comment on those methodological issues we think most important. These include alpha assessment, training schedules, and uni- versus bidirectional training. This analysis is accomplished in part by a series of tables listing 45 studies and the detailed methodologies used. It is believed that the probabilities of successful feedback enhancement of alpha can be substantially improved by incorporating the following suggestions: (a) employing at least four training sessions, (b) the use of continuous rather than dichotomous feedback, supplemented by periodic quantitative scores of progress, and (c) using training trials of at least 10 minutes' duration.

A total of 68 subjects participated in two experiments that tested the effect of exposure to comedy upon amount of discordant right-left occipital EEG alpha. Data from both showed less discordant alpha in the “laughers” and more in the “nonlaughers” at the end of exposure to a filmed comedy, as contrasted by no such group difference before treatment. Experiment 2 clarified that the production of discordant alpha in the right hemisphere was significant to this group difference, that this effect was specific to comedy treatment (nondiscriminative effects of exposure to a neutral film), and that a reversed group difference in amount of discordant right hemisphere alpha occurred after instructed hypoventilation (nondiscriminative effect of hyperventilation; counterbalanced order of all four treatments). The results were discussed in relation to (a) recent findings on right-left hemisphere characteristics of depressed individuals, (b) the significance of motivational states, (c) a link between cerebral blood flow and EEG indicators of activation, (d) ventilatory effects upon cortical activation, (e) personality differences inherent in tolerance for CO2-blood concentration, and (f) recent findings on corticothalamic connections.

The study examined whether complete omission of a tone stimulus following its repeated presentation would elicit an electrodermal orienting response and whether the factors of stimulus significance and subject lability influenced the probability and magnitude of any response to omission. A statistically significant increase in response on omission trials over that in control periods without stimulation preceding omission was observed. The omission effect was more likely to occur with labile subjects, those showing high levels of nonspecific electrodermal activity, than with stabiles; stimulus significance was not found to exert any systematic effect. Contrary to expectation, a measure of EEG alpha activity included in the study failed to show the omission effect. The failure was attributed to problems of measurement. Incidental findings of the study refute an arousal interpretation of electrodermal lability.

Success or failure of EEG feedback training for alpha enhancement can depend on how alpha activity is quantified and fed back. Alpha-enhancement failures usually employ a percent time(%) technique; successes typically use amplitude integration(e). To dramatize the differences between percent and integration techniques, we derived both measures simultaneously from left occipital(O 1 ) and left central(C 3 ) sites for 16 male subjects who were given 5.6 hours of integrated alpha feedback from the midline occipital(Oz ) site. At both the O 1 and C 3 sites the integrated and percent measures were not equivalent and not linearly related. Statistically significant differences in the(integrated, percent) correlation coefficients(z-transformed) were observed under the different recording conditions: alpha enhancement, alpha enhancement, alpha suppression, and baselines. Theoretical discussion of integration and percent techniques is given and the adoption of amplitude integration measures and feedback stimuli is strongly advocated.

Six normal adults looked at 12 color transparencies that were presented 30 times each in response to the occurrence of alpha in the occipital EEG and that were not presented when no-alpha occurred. The time delay between the occurrence of recorded EEG alpha and the feedback stimulus was systematically varied, as was the threshold value of alpha amplitude required for feedback stimulus to occur. As time delay increased, the replicative reliability of the temporal association between alpha and the visual stimulus decreased. The measures of the EEG response were: the mean durations of alpha and of no-alpha durations\((\bar X)\); an estimate of random “scatter” or variability in a single trial (Se); and the ratio of these\(({{\bar X} \mathord{\left/ {\vphantom {{\bar X} S}} \right. \kern-\nulldelimiterspace} S}_e )\), which is the reciprocal of the coefficient of variation. The latter ratio defines “control” of the EEG response. Control was greatest for the minimum feedback delay (.25 sec) and a feedback threshold of 25% of the maximum peak alpha amplitude recorded under a prior eyes-closed. “resting” condition. Control of the EEG decreased as time delays increased and at lower and higher feedback thresholds. It was proposed that the measurement of control\(({{\bar X} \mathord{\left/ {\vphantom {{\bar X} S}} \right. \kern-\nulldelimiterspace} S}_e )\) for various combinations of values of relevant experimental parameters could be used to select that combination which gave the best control. This “optimum” combination of values of parameters could be chosen for astandardized method.

Integrated EEG alpha was recorded from T 3 and T 4 . Larger Rα/Lα ratios were defined as right asymmetry, relatively smaller ratios as left asymmetry. In different phases of the study, participants attempted to identify the presence of the EEG asymmetries and to produce the EEG asymmetries during auditory biofeedback, and were tested on hemisphere-specialized cognitive tasks while attempting to produce the EEG asymmetries. Experiential descriptions of the EEG asymmetries were obtained throughout using a set of bipolar scales. Some participants were able to identify the presence of the EEG asymmetries (p

Two experiments examined the relationship between time domain patterns of EEG activity and self-reports for individuals exposed to different odorants. In the first experiment, spiced apple, eucalyptus, and lavender odors were evaluated. The three odorants produced consistently different patterns of EEG theta activity and self-reports. These results suggest that odor administration is a reliable variable in manipulating neurophysiological response systems and may be influential in affecting human performance and mood. In order to assess the sensitivity of EEG in the delineation of odor effects, a second experiment was conducted. EEG activity was recorded while subjects smelled five similar commercial odorous chemicals and an unscented base. Subjects completed questionnaires on odor character and mood following each presentation. Results of the experiment indicated little perceptual or mood difference produced by the odors. EEG alpha and theta activity in the left and right hemispheres, however, differed widely depending upon the odor presented and was dissociated from self-report. These results suggest the sensitivity of EEG techniques in odor experiments and indicate that the perceptual component of olfaction accounts for only a limited part of the central nervous system changes produced by smelling an odor.

A two-channel general-purpose EEG alpha-detection system is described, along with the associated computer hardware and software. A specific application for the study of the human orienting response using alpha-contingent visual stimulation is presented. Limitations are discussed.

Magnitude and duration of EEG alpha desynchronization were taken as indicators of the orienting response, and the relationship of these measures to intensity of visual stimulation was investigated. The two measures selected were found to vary with stimulus intensity, although each measure exhibited a different trend over stimulus intensity.

Level of arousal as indicated by the amplitude of the EEG alpha rhythm was continuously recorded from 40 Ss while their two flash thresholds were measured. A significant correlation (r=+.56) found between the two variables was interpreted as supporting the theory that 2FT is a measure of arousal. Additional evidence from other sources is considered, and a reason why the correlation is not higher is offered.

EEG activity and eye movements were recorded while Ss inspected a Ganzfeld or diffuse dark figures introduced into a Ganzfeld. Reports of deterioration of visual perception under all stimulus conditions were preceded by a period of reduced eye movement, but were not associated with a return of EEG alpha activity.

A CONJUGATE lateral eye movement has been observed in humans in association with the shift from external to internal direction of attention1. When asked a question requiring reflexion (for example, mental arithmetic) an individual normally shifts his eyes either to the right or the left as he begins to reflect on an answer. It has been suggested that the direction of this lateral eye movement is related to a characteristic deployment of attention; left movers show a greater tendency to focus attention on internal subjective experiences, right movers show a greater tendency to external focus of attention2. It has been found that subjects who tend to move their eyes to the left are more likely to be hypnotizable3. Hypnotizability has also been shown to be related to amount of EEG alpha activity during an eyes-closed resting condition4,5. The relationship of both lateral direction of eye movements and amount of EEG alpha activity to hypnotizability seems to indicate the need for a study of the relationship between amount of resting EEG alpha activity and the direction of reflective lateral eye movements. This study was designed to test the hypothesis that the tendency to move the eyes to the left is associated with more EEG alpha activity than is the tendency to move the eyes to the right.