Alpha Amplitude Research Articles

Differences in Brain Waves and Blood Pressure by Listening to Quran-e-Kareem and Music

Background: Quranic recitation and music do not share any features in terms of content besides the use of melodies, but it is a common belief, that both have positive effect on reducing blood pressure and anxiety level of patients. This research investigates and compares the effects of listening to Quranic recitation and soft music on human brain waves especially Alpha and Beta waves by electroencephalogram (EEG) using Power-Lab.Material and Methods: A clinical trial was carried out in the Physiology Department of Islamabad Medical and Dental College. There were 22 participants, divided into two groups (A and B) with 11 participants in each group. Group A included students with ages 20-25 years and Group B comprised of teaching faculty between 40-60 years. All the study participants were Urdu-speaking, Pakistani Muslims having normal hearing. Sample selection was based on non-random convenient sampling. Paired T-test was used to compare means of Alpha and Beta waves amplitude, with p value < 0.05 considered as statistically significant.Results: Listening to Quranic recitation results in greater amplitude of Alpha waves in both younger and older age groups (p=0.01). The cross comparisons of systolic blood pressure at rest and after music for Group A showed significant results (p=0.04) indicating that soft music increases systolic blood pressure in younger people. Diastolic blood pressure comparison proves that it decreases by Tilawat in older age-groups (p<0.05).Conclusion: EEG showed that Quran generates comparatively higher amplitudes of Alpha than Beta waves, which reflects the calmness and relaxation of the participants while listening to Quranic recitation. Furthermore, there was a mild reduction in diastolic blood pressure in older subjects after listening to Quranic recitation.

ИЗМЕНЕНИЕ ПАТТЕРНА ЭЛЕКТРОЭНЦЕФАЛОГРАММЫ У ПРАВШЕЙ И ЛЕВШЕЙ ПРИ ВООБРАЖЕНИИ ДВИЖЕНИЙ

The objective of the paper is to analyze changes in electroencephalogram (EEG) pattern in right- and left-handers during imaginary movements of leading and non-leading legs. Materials and Methods. The authors examined 40 right-handers and 20 left-handers, whose motor domination profile was determined by standard tests. EEGs were recorded at rest and during imaginary rotational movements of the right and left legs. NVX 36 digital DC EEG neurovisor, “10–20” system, was used for this perpose. The authors also analyzed the amplitude of the EEG rhythms (standard frequency ranges), evaluated changes in hemispheric asymmetry coefficients of frontal and central alpha and beta1 rhythms as EEG correlates of imaginary activity. Results. Imaginary movements caused a decrease in the amplitude of alpha, beta1, theta and delta rhythms on EEG in all trial subjects. The intensity of observed changes in right- and left-handers differed in symmetrical leads. As for frontal and central alpha and beta1 rhythms, which marked changes in the EEG pattern during imaginary movements, right-handers demonstrated that their depression level in symmetric cortical areas depended significantly on the imaginary movements of leading and non-leading legs and dominated in left or right hemispheres, respectively. For left-handers, changes in alpha and beta1 waves during imaginary movements of leading and non-leading legs did not differ significantly and in both cases dominated in the right hemisphere. Conclusion. Thus, the intra- and inter-hemispheric dynamics of the EEG pattern, while forming the concept and program of complex motor leg actions in left-handers, is alternative in comparison to right-handers. Keywords: EEG, alpha rhythm, beta1 rhythm, imaginary leg movements, hemispheric asymmetry, right-handers, left-handers.

Cortical distance, not cancellation, dominates inter-subject EEG gamma rhythm amplitude

The neurophysiological response to visual stimulation in both humans and animals is characterized by an increase in high frequency amplitude peaking in the gamma range (40–100Hz) and a suppression of low frequency amplitude peaking in the alpha range (10–16Hz). Due to the large number of studies linking amplitude and peak frequency to perception and neurological disorders, there is great interest in understanding the basis of inter-subject variability in gamma and alpha responses. To address this, we measured gamma and alpha amplitude and peak frequency of response to visual stimulation in 42 healthy humans. Using FMRI to delineate active cortical tissue in the same subjects, we correlated these neurophysiological metrics with two structural metrics: distance from active cortex to electrode, and dipole cancellation over active cortex. We find that distance strongly predicted inter-subject gamma amplitude, but had little effect on alpha amplitude, while cancellation had little effect on gamma or alpha amplitude. Neither alpha peak frequency nor gamma peak frequency correlated with our structural metrics. These results suggest that inter-subject variability in gamma amplitude may reflect gross morphology rather than neurophysiological variability, and should be interpreted with caution, while peak frequency may serve as a more sensitive metric of differences in neuronal activity across subjects.

Design and Implementation of an Asynchronous BCI System With Alpha Rhythm and SSVEP

Objective : The aim of this work was to build an asynchronous brain-computer interface (BCI) system based on steady-state visual evoked potentials (SSVEPs) that outputs continuous, stable and smooth control commands in the up, down, left and right directions. Real-time feedback is presented on the computer screen to enhance collaborative participation in the human-computer interaction. Methods : Four stimulus sources flickering at different frequencies were sequentially fixed around the computer monitor to allow for subjects to complete control tasks by gazing at different stimulus sources. The subjects autonomously switched between the idle and working states by controlling the alpha amplitude. A sliding window voting discrimination (SWVD) strategy was incorporated into the canonical correlation analysis (CCA) algorithm for asynchronous classification. Results : Experiments were performed with 18 subjects using both the synchronous and asynchronous paradigms. The average accuracy was 95.42±3.35% with a data length of 3 s for synchronous operation; in addition, most subjects were able to successfully control a target to move precisely and smoothly with a 1 s sliding window during asynchronous operation. Conclusion : The proposed design scheme is feasible for our online asynchronous BCI system. Significance : By applying the SWVD strategy and optimizing the experimental paradigm, the classical CCA algorithm was successfully applied for continuous control in an asynchronous BCI system. With the developed system, obvious improvements in the information transmission rate (ITR) and sensitivity were achieved, which will be beneficial for the development of practical BCI systems.

Long-range temporal correlations in the brain distinguish conscious wakefulness from induced unconsciousness

Rhythmic neuronal synchronization across large-scale networks is thought to play a key role in the regulation of conscious states. Changes in neuronal oscillation amplitude across states of consciousness have been widely reported, but little is known about possible changes in the temporal dynamics of these oscillations. The temporal structure of brain oscillations may provide novel insights into the neural mechanisms underlying consciousness. To address this question, we examined long-range temporal correlations (LRTC) of EEG oscillation amplitudes recorded during both wakefulness and anesthetic-induced unconsciousness. Importantly, the time-varying EEG oscillation envelopes were assessed over the course of a sevoflurane sedation protocol during which the participants alternated between states of consciousness and unconsciousness. Both spectral power and LRTC in oscillation amplitude were computed across multiple frequency bands. State-dependent differences in these features were assessed using non-parametric tests and supervised machine learning. We found that periods of unconsciousness were associated with increases in LRTC in beta (15–30Hz) amplitude over frontocentral channels and with a suppression of alpha (8–13Hz) amplitude over occipitoparietal electrodes. Moreover, classifiers trained to predict states of consciousness on single epochs demonstrated that the combination of beta LRTC with alpha amplitude provided the highest classification accuracy (above 80%). These results suggest that loss of consciousness is accompanied by an augmentation of temporal persistence in neuronal oscillation amplitude, which may reflect an increase in regularity and a decrease in network repertoire compared to the brain's activity during resting-state consciousness.

ОСОБЕННОСТИ БИОЭЛЕКТРИЧЕСКОЙ АКТИВНОСТИ ГОЛОВНОГО МОЗГА СТУДЕНТОК ВЫПУСКНОГО КУРСА В ЗАВИСИМОСТИ ОТ ИХ УРОВНЯ ТРЕВОЖНОСТИ

Aim. This article deals with the assessment of the bioelectric activity of the brain in finalyear female students depending on their anxiety level. Materials and methods. The study involved 32 final-year female students in the intersession period and 24 female students in the session period. The amplitude, frequency and EEG rhythm index were established using EEG spectral analysis. We also used the coherent analysis of EEG to reveal connections between different areas of the brain. Results. Higher situational anxiety is characterized by the increased coherence and decreased amplitude of alpha and theta rhythm. The analysis of EEG frequencies demonstrated the differences between the intersession and session periods only for a theta range. Theta activity dominated in female students with lower personal anxiety. In the session period in comparison with the intersession period we registered the highest values of theta rhythm in the frontal lobes in female students with high personal anxiety. Increased coherence was registered mainly in fronto-central and centro-temporal areas of the right hemisphere. In participants with low situational anxiety we established decreased coherence in the left temporal area for alpha rhythm and in the right fronto-central and left fronto-temporal areas for beta rhythm. In the intersession period in girls with low situational anxiety we registered decreased coherence in the left parieto-occipital, left fronto-parietal and right fronto-temporal areas for a beta range and in the right fronto-parietal area for theta rhythm. The most significant theta activity was registered in students with moderate personal anxiety in upper-frontal, central, left parietal, left occipital and right lower frontal areas. Conclusions. For the majority of female students low situational and high personal anxiety were typical for intersession and session periods. Girls with low situational anxiety were characterized by an increase in the amplitude of alpha rhythm during the intersession period and by an increase in theta rhythm in the session period.

Temporal stability of posterior EEG alpha over twelve years

ObjectiveWe previously identified posterior EEG alpha as a potential biomarker for antidepressant treatment response. To meet the definition of a trait biomarker or endophenotype, it should be independent of the course of depression. Accordingly, this report evaluated the temporal stability of posterior EEG alpha at rest. MethodsResting EEG was recorded from 70 participants (29 male; 46 adults), during testing sessions separated by 12 ± 1.1 years. EEG alpha was identified, separated and quantified using reference-free methods that combine current source density (CSD) with principal components analysis (PCA). Measures of overall (eyes closed-plus-open) and net (eyes closed-minus-open) posterior alpha amplitude and asymmetry were compared across testing sessions. ResultsOverall alpha was stable for the full sample (Spearman-Brown [rSB] = .834, Pearson's r = .718), and showed excellent reliability for adults (rSB = .918; r = 0.848). Net alpha showed acceptable reliability for adults (rSB = .750; r = .600). Hemispheric asymmetries (right-minus-left hemisphere) of posterior overall alpha showed significant correlations, but revealed acceptable reliability only for adults (rSB = .728; r = .573). Findings were highly comparable between 29 male and 41 female participants. ConclusionsOverall posterior EEG alpha amplitude is reliable over long time intervals in adults. SignificanceThe temporal stability of posterior EEG alpha oscillations at rest over long time intervals is indicative of an individual trait.

The peculiarities of brain bioelectrical activity in infants who suffered from stress due to military conflict depending on type of feeding

The aim of the research is to study the peculiarities of brain electrical activity in infants who suffered from stress due to military conflict and who were on different types of feeding.
 An electroencephalographic study was conducted in 68 infants who were in the military conflict zone and formed the main group. These infants were divided into 2 subgroups. Subgroup Ia included 36 infants who were breastfeeding. Subgroup Ib included 32 infants who were on artificial feeding. EEG was also made to 88 children who made up a control group and were outside the zone of military conflict. Of these, 47 children were breastfed, who entered the subgroup IIa and 41 children were on artificial feeding, included in subgroup IIb.
 The study was carried out with the help of a hardware-software complex for recording and processing electroencephalograms and evoked potentials DX-NT 32.
 The most pronounced physiological changes in brain bioelectrical activity were detected in the group of children undergoing stress of war and being on artificial feeding, which were manifested by lower parameters of the amplitude, frequency and time index of alpha and beta rhythms, increased amplitude, frequency and time index of delta and theta rhythms.

The role of thromboelastography in predicting hemorrhage risk in patients with leukemia.

This study aimed to compare the efficacy of thromboelastography (TEG) and conventional coagulation methods in predicting hemorrhage risk in patients with leukemia.A total of 226 patients diagnosed with leukemia were included and divided into bleeding and nonbleeding groups. All patients had their blood samples taken for TEG test to measure the reaction time (R time), alpha (α angle), and maximum amplitude (MA) as well as measure platelet count (PLT), prothrombin time, and activated partial thromboplastin time. Patients were followed up for bleeding episodes.The multivariate analysis showed that PLT [odds ratio (OR) = 0.993] and MA (OR = 0.921) have better association with bleeding risk. Receiver operating characteristic (ROC) analysis showed that the combination of PLT and MA (AUC = 0.824) was better for hemorrhage risk prediction than PLT [area under the curve (AUC) = 0.730] and MA (AUC = 0.819) alone.The combination of TEG and conventional coagulation methods could help in assessing the risk of hemorrhage in patients with leukemia.

On the Efficiency of Individualized Theta/Beta Ratio Neurofeedback Combined with Forehead EMG Training in ADHD Children.

Background: Neurofeedback training (NFT) to decrease the theta/beta ratio (TBR) has been used for treating hyperactivity and impulsivity in attention deficit hyperactivity disorder (ADHD); however, often with low efficiency. Individual variance in EEG profile can confound NFT, because it may lead to influencing non-relevant activity, if ignored. More importantly, it may lead to influencing ADHD-related activities adversely, which may even result in worsening ADHD symptoms. Electromyogenic (EMG) signal resulted from forehead muscles can also explain the low efficiency of the NFT in ADHD from both practical and psychological point-of-view. The first aim of this study was to determine EEG and EMG biomarkers most related to the main ADHD characteristics, such as impulsivity and hyperactivity. The second aim was to confirm our hypothesis that the efficiency of the TBR NFT can be increased by individual adjustment of the frequency bands and simultaneous training on forehead muscle tension.Methods: We recruited 94 children diagnosed with ADHD (ADHD) and 23 healthy controls (HC). All participants were male and aged between six and nine. Impulsivity and attention were assessed with Go/no-Go task and delayed gratification task, respectively; and 19-channel EEG and forehead EMG were recorded. Then, the ADHD group was randomly subdivided into (1) standard, (2) individualized, (3) individualized+EMG, and (4) sham NFT (control) groups. The groups were compared based on TBR and EEG alpha activity, as well as hyperactivity and impulsivity three times: pre-NFT, post-NFT and 6 months after the NFT (follow-up).Results: ADHD children were characterized with decreased individual alpha peak frequency, alpha bandwidth and alpha amplitude suppression magnitude, as well as with increased alpha1/alpha2 (a1/a2) ratio and scalp muscle tension when c (η2 ≥ 0.212). All contingent TBR NFT groups exhibited significant NFT-related decrease in TBR not evident in the control group. Moreover, we detected a higher overall alpha activity in the individualized but not in the standard NFT group. Mixed MANOVA considering between-subject factor GROUP and within-subject factor TIME showed that the individualized+EMG group exhibited the highest level of clinical improvement, which was associated with increase in the individual alpha activity at the 6 months follow-up when comparing with the other approaches (post hoc t = 3.456, p = 0.011).Conclusions: This study identified various (adjusted) alpha activity metrics as biomarkers with close relationship with ADHD symptoms, and demonstrated that TBR NFT individually adjusted for variances in alpha activity is more successful and clinically more efficient than standard, non-individualized NFT. Moreover, these training effects of the individualized TBR NFT lasted longer when combined with EMG.

EEG Responses to Shamanic Drumming. Does the Suggestion of Trance State Moderate the Strength of Frequency Components?

One of the techniques used to induce trance state in shamanic ceremonies is monotonous drumming. According to previous EEG research, certain patterns of drumming cause an increase in power of alpha and theta frequencies of the listener. Present study aimed to determine, if suggestion to experience trance state could increase the relative alpha and theta amplitude and the intensity of experienced state. A group of twenty-four subjects participated in the study. Suggestion to experience trance state decreased alpha frequency power during the drumming condition. No other significant effects of suggestion or drumming were found.

Different responses of spontaneous and stimulus-related alpha activity to ambient luminance changes.

Alpha oscillations are particularly important in determining our percepts and have been implicated in fundamental brain functions. Oscillatory activity can be spontaneous or stimulus-related. Furthermore, stimulus-related responses can be phase- or non-phase-locked to the stimulus. Non-phase-locked (induced) activity can be identified as the average amplitude changes in response to a stimulation, while phase-locked activity can be measured via reverse-correlation techniques (echo function). However, the mechanisms and the functional roles of these oscillations are far from clear. Here, we investigated the effect of ambient luminance changes, known to dramatically modulate neural oscillations, on spontaneous and stimulus-related alpha. We investigated the effect of ambient luminance on EEG alpha during spontaneous human brain activity at rest (experiment 1) and during visual stimulation (experiment 2). Results show that spontaneous alpha amplitude increased by decreasing ambient luminance, while alpha frequency remained unaffected. In the second experiment, we found that under low-luminance viewing, the stimulus-related alpha amplitude was lower, and its frequency was slightly faster. These effects were evident in the phase-locked part of the alpha response (echo function), but weaker or absent in the induced (non-phase-locked) alpha responses. Finally, we explored the possible behavioural correlates of these modulations in a monocular critical flicker frequency task (experiment 3), finding that dark adaptation in the left eye decreased the temporal threshold of the right eye. Overall, we found that ambient luminance changes impact differently on spontaneous and stimulus-related alpha expression. We suggest that stimulus-related alpha activity is crucial in determining human temporal segmentation abilities.

Taking off the training wheels: Measuring auditory P3 during outdoor cycling using an active wet EEG system

Mobile EEG allows the investigation of brain activity in increasingly complex environments. In this study, EEG equipment was adapted for use and transportation in a backpack while cycling. Participants performed an auditory oddball task while cycling outside and sitting in an isolated chamber inside the lab. Cycling increased EEG noise and marginally diminished alpha amplitude. However, this increased noise did not influence the ability to measure reliable event related potentials (ERP). The P3 was similar in topography, and morphology when outside on the bike, with a lower amplitude in the outside cycling condition. There was only a minor decrease in the statistical power to measure reliable ERP effects. Unexpectedly, when biking outside significantly decreased P2 and increased N1 amplitude were observed when evoked by both standards and targets compared with sitting in the lab. This may be due to attentional processes filtering the overlapping sounds between the tones used and similar environmental frequencies. This study established methods for mobile recording of ERP signals. Future directions include investigating auditory P2 filtering inside the laboratory.

Fluctuations in instantaneous frequency predict alpha amplitude during visual perception

Rhythmic neural activity in the alpha band (8–13 Hz) is thought to have an important role in the selective processing of visual information. Typically, modulations in alpha amplitude and instantaneous frequency are thought to reflect independent mechanisms impacting dissociable aspects of visual information processing. However, in complex systems with interacting oscillators such as the brain, amplitude and frequency are mathematically dependent. Here, we record electroencephalography in human subjects and show that both alpha amplitude and instantaneous frequency predict behavioral performance in the same visual discrimination task. Consistent with a model of coupled oscillators, we show that fluctuations in instantaneous frequency predict alpha amplitude on a single trial basis, empirically demonstrating that these metrics are not independent. This interdependence suggests that changes in amplitude and instantaneous frequency reflect a common change in the excitatory and inhibitory neural activity that regulates alpha oscillations and visual information processing.

Coupling of Oxy- and Deoxyhemoglobin concentrations with EEG rhythms during motor task

A relationship between the brain rhythmic activity and the hemodynamic response was studied using the simultaneous measurement of electroencephalogram (EEG) and the functional near-infrared spectroscopy (fNIRS) during a motor task (self-paced right finger movements) for 10 subjects. An EEG recording with a 32-electrode (10-10) system was made and the hemodynamic response was obtained using 8 optodes placed over the sensorimotor cortex on both hemispheres. During the task an increase in oxyhemoglobine (HbO) was accompanied by a decrease in deoxyhemoglobine (HbR) concentration and a decrease in amplitudes (desynchronisation) of alpha (8–13 Hz) and beta (13–30 Hz) EEG rhythms. These phenomena were prominent in the hemisphere contralateral to the moving finger. The delays between the hemodynamic and electrophysiological variables were on average 2.8 s. Highly significant (p < 0.0001) negative Pearson correlations were found between HbO and alpha (r2 = −0.69) and HbO and beta (r2 = −0.54) rhythms. Positive correlations r2 = 0.5 between these rhythms and HbR were found.

Central theta amplitude as a negative correlate of performance proficiency in a dynamic visuospatial task

Dynamic visuospatial tasks, requiring continuous engagement of attention over long time periods, have been little studied with the electroencephalogram. Specifically, the role of the theta band in these tasks is unclear, with task-related theta enhancements improving performance in some studies, and hindering it in others. In this study, 30 participants performed the Pong videogame as a dynamic visuospatial task to analyze the influence of theta and alpha amplitude as well as alpha asymmetry on performance. The theta band increased significantly at central-parietal regions and correlated negatively with performance, especially at anterior regions. The alpha band showed a significant decrease, greater at right over left parietal regions, but neither the amplitude nor the asymmetry ratio correlated with performance. With theta being an indicator of top-down cognitive control, it may be concluded that proficient performance in dynamic visuospatial tasks depends on a bottom-up guidance of attention with little top-down intervention.

Modulation of Somatosensory Alpha Rhythm by Transcranial Alternating Current Stimulation at Mu-Frequency.

Introduction: Transcranial alternating current stimulation (tACS) is emerging as an interventional tool to modulate different functions of the brain, potentially by interacting with intrinsic ongoing neuronal oscillations. Functionally different intrinsic alpha oscillations are found throughout the cortex. Yet it remains unclear whether tACS is capable of specifically modulating the somatosensory mu-rhythm in amplitude.Objectives: We used tACS to modulate mu-alpha oscillations in amplitude. When compared to sham stimulation we expected a modulation of mu-alpha oscillations but not visual alpha oscillations by tACS.Methods: Individual mu-alpha frequencies were determined in 25 participants. Subsequently, blocks of tACS with individual mu-alpha frequency and sham stimulation were applied over primary somatosensory cortex (SI). Electroencephalogram (EEG) was recorded before and after either stimulation or sham. Modulations of mu-alpha and, for control, visual alpha amplitudes were then compared between tACS and sham.Results: Somatosensory mu-alpha oscillations decreased in amplitude after tACS was applied at participants’ individual mu-alpha frequency. No changes in amplitude were observed for sham stimulation. Furthermore, visual alpha oscillations were not affected by tACS or sham, respectively.Conclusion: Our results demonstrate the capability of tACS to specifically modulate the targeted somatosensory mu-rhythm when the tACS frequency is tuned to the individual endogenous rhythm and applied over somatosensory areas. Our results are in contrast to previously reported amplitude increases of visual alpha oscillations induced by tACS applied over visual cortex. Our results may point to a specific interaction between our stimulation protocol and the functional architecture of the somatosensory system.

Aging affects the balance of neural entrainment and top-down neural modulation in the listening brain

Healthy aging is accompanied by listening difficulties, including decreased speech comprehension, that stem from an ill-understood combination of sensory and cognitive changes. Here, we use electroencephalography to demonstrate that auditory neural oscillations of older adults entrain less firmly and less flexibly to speech-paced (∼3 Hz) rhythms than younger adults’ during attentive listening. These neural entrainment effects are distinct in magnitude and origin from the neural response to sound per se. Non-entrained parieto-occipital alpha (8–12 Hz) oscillations are enhanced in young adults, but suppressed in older participants, during attentive listening. Entrained neural phase and task-induced alpha amplitude exert opposite, complementary effects on listening performance: higher alpha amplitude is associated with reduced entrainment-driven behavioural performance modulation. Thus, alpha amplitude as a task-driven, neuro-modulatory signal can counteract the behavioural corollaries of neural entrainment. Balancing these two neural strategies may present new paths for intervention in age-related listening difficulties.

Frontal Alpha Oscillations and Attentional Control: A Virtual Reality Neurofeedback Study

Two competing views about alpha oscillations suggest that cortical alpha reflect either cortical inactivity or cortical processing efficiency. We investigated the role of alpha oscillations in attentional control, as measured with a Stroop task. We used neurofeedback to train 22 participants to increase their level of alpha amplitude. Based on the conflict/control loop theory, we selected to train prefrontal alpha and focus on the Gratton effect as an index of deployment of attentional control. We expected an increase or a decrease in the Gratton effect with increase in neural learning depending on whether frontal alpha oscillations reflect cortical idling or enhanced processing efficiency, respectively. In order to induce variability in neural learning beyond natural occurring individual differences, we provided half of the participants with feedback on alpha amplitude in a 3-dimensional (3D) virtual reality environment and the other half received feedback in a 2D environment. Our results showed variable neural learning rates, with larger rates in the 3D compared to the 2D group, corroborating prior evidence of individual differences in EEG-based learning and the influence of a virtual environment. Regression analyses revealed a significant association between the learning rate and changes on deployment of attentional control, with larger learning rates being associated with larger decreases in the Gratton effect. This association was not modulated by feedback medium. The study supports the view of frontal alpha oscillations being associated with efficient neurocognitive processing and demonstrates the utility of neurofeedback training in addressing theoretical questions in the non-neurofeedback literature.

Alpha-Band Brain Oscillations Shape the Processing of Perceptible as well as Imperceptible Somatosensory Stimuli during Selective Attention.

Attention filters and weights sensory information according to behavioral demands. Stimulus-related neural responses are increased for the attended stimulus. Does alpha-band activity mediate this effect and is it restricted to conscious sensory events (suprathreshold), or does it also extend to unconscious stimuli (subthreshold)? To address these questions, we recorded EEG in healthy male and female volunteers undergoing subthreshold and suprathreshold somatosensory electrical stimulation to the left or right index finger. The task was to detect stimulation at the randomly alternated cued index finger. Under attention, amplitudes of somatosensory evoked potentials increased 50-60 ms after stimulation (P1) for both suprathreshold and subthreshold events. Prestimulus amplitude of peri-Rolandic alpha, that is mu, showed an inverse relationship to P1 amplitude during attention compared to when the finger was unattended. Interestingly, intermediate and high amplitudes of mu rhythm were associated with the highest P1 amplitudes during attention and smallest P1 during lack of attention, that is, these levels of alpha rhythm seemed to optimally support the behavioral goal ("detect" stimuli at the cued finger while ignoring the other finger). Our results show that attention enhances neural processing for both suprathreshold and subthreshold stimuli and they highlight a rather complex interaction between attention, Rolandic alpha activity, and their effects on stimulus processing.SIGNIFICANCE STATEMENT Attention is crucial in prioritizing processing of relevant perceptible (suprathreshold) stimuli: it filters and weights sensory input. The present study investigates the controversially discussed question whether this attention effect extends to imperceptible (subthreshold) stimuli as well. We found noninvasive EEG signatures for attentional modulation of neural events following perceptible and imperceptible somatosensory stimulation in human participants. Specifically, stimulus processing for both kinds of stimulation, subthreshold and suprathreshold, is enhanced by attention. Interestingly, Rolandic alpha rhythm strength and its influence on stimulus processing are strikingly altered by attention most likely to optimally achieve the behavioral goal.