Increase In Alpha Band Power Research Articles

Neuromodulatory Effects of HD-tACS/tDCS on the Prefrontal Cortex: A Resting-State fNIRS-EEG Study.

Transcranial direct and alternating current stimulation (tDCS and tACS, respectively) can modulate human brain dynamics and cognition. However, these modalities have not been compared using multiple imaging techniques concurrently. In this study, 15 participants participated in an experiment involving two sessions with a gap of 10 days. In the first and second sessions, tACS and tDCS were administered to the participants. The anode for tDCS was positioned at point FpZ, and four cathodes were positioned over the left and right prefrontal cortices (PFCs) to target the frontal regions simultaneously. tDCS was administered with 1 mA current. tACS was supplied with a current of 1 mA (zero-to-peak value) at 10 Hz frequency. Stimulation was applied concomitantly with functional near-infrared spectroscopy and electroencephalography acquisitions in the resting-state. The statistical test showed significant alteration (p < 0.001) in the mean hemodynamic responses during and after tDCS and tACS periods. Between-group comparison revealed a significantly less (p < 0.001) change in the mean hemodynamic response caused by tACS compared with tDCS. As hypothesized, we successfully increased the hemodynamics in both left and right PFCs using tDCS and tACS. Moreover, a significant increase in alpha-band power (p < 0.01) and low beta band power (p < 0.05) due to tACS was observed after the stimulation period. Although tDCS is not frequency-specific, it increased but not significantly (p > 0.05) the powers of most bands including delta, theta, alpha, low beta, high beta, and gamma. These findings suggest that both hemispheres can be targeted and that both tACS and tDCS are equally effective in high-definition configurations, which may be of clinical relevance.

337 Neural Network Changes with Loss of Consciousness in Parkinson's Disease

INTRODUCTION: Consciousness is likely mediated by multiple parallel yet interacting cortico-subcortical recurrent networks. The pallidocortical circuit is of particular interest given the putative role of pallidum in consciousness, according to the mesocircuit model, though this has not been well studied. METHODS: We characterized changes in pallidocortical circuits in awake versus propofol-induced unconscious states in humans by directly and simultaneously recording from perirolandic cortices and the pallidum in twelve Parkinson Disease (PD) patients undergoing implantation of therapeutic deep brain stimulation (DBS) leads. RESULTS: Propofol-induced LOC resulted in power increases up to 20 Hz in globus pallidus internus (GPi), 35 Hz in globus pallidus externus (GPe), and 100 Hz in sensorimotor cortices (S1/M1). At a network level, LOC resulted in increased pallidocortical alpha coherence with increases in Granger causality (GC) in the alpha/low beta range from GPe to all other nodes. In contrast, LOC was associated with decreased network-wide beta coherence with decreased GC in the beta range from M1 to the rest of the network. CONCLUSION: These results not only confirm the LOC-related changes in pallidocortical circuitry, but GC results suggest that widely reported LOC-related increases in alpha band power emanate from GPe. These findings support a significant role of the GPe in modulating consciousness. Simultaneous LOC-related suppression of beta synchrony from M1 to other nodes suggests that distinct oscillatory frequencies can act independently, conveying unique network level activity. Given the pathophysiologic role of beta synchrony in PD, LOC-related suppresion of beta synchrony may be amplified in this patient population, but may also highlight a parallel network mediating LOC-related loss of motor control.

Electrophysiological Brain Changes Associated With Cognitive Improvement in a Pediatric Attention Deficit Hyperactivity Disorder Digital Artificial Intelligence-Driven Intervention: Randomized Controlled Trial.

BackgroundCognitive stimulation therapy appears to show promising results in the rehabilitation of impaired cognitive processes in attention deficit hyperactivity disorder.ObjectiveEncouraged by this evidence and the ever-increasing use of technology and artificial intelligence for therapeutic purposes, we examined whether cognitive stimulation therapy implemented on a mobile device and controlled by an artificial intelligence engine can be effective in the neurocognitive rehabilitation of these patients.MethodsIn this randomized study, 29 child participants (25 males) underwent training with a smart, digital, cognitive stimulation program (KAD_SCL_01) or with 3 commercial video games for 12 weeks, 3 days a week, 15 minutes a day. Participants completed a neuropsychological assessment and a preintervention and postintervention magnetoencephalography study in a resting state with their eyes closed. In addition, information on clinical symptoms was collected from the child´s legal guardians.ResultsIn line with our main hypothesis, we found evidence that smart, digital, cognitive treatment results in improvements in inhibitory control performance. Improvements were also found in visuospatial working memory performance and in the cognitive flexibility, working memory, and behavior and general executive functioning behavioral clinical indexes in this group of participants. Finally, the improvements found in inhibitory control were related to increases in alpha-band power in all participants in the posterior regions, including 2 default mode network regions of the interest: the bilateral precuneus and the bilateral posterior cingulate cortex. However, only the participants who underwent cognitive stimulation intervention (KAD_SCL_01) showed a significant increase in this relationship.ConclusionsThe results seem to indicate that smart, digital treatment can be effective in the inhibitory control and visuospatial working memory rehabilitation in patients with attention deficit hyperactivity disorder. Furthermore, the relation of the inhibitory control with alpha-band power changes could mean that these changes are a product of plasticity mechanisms or changes in the neuromodulatory dynamics.Trial RegistrationISRCTN Registry ISRCTN71041318; https://www.isrctn.com/ISRCTN71041318

P-EG002. An exploratory study of brain waves and corresponding brain regions of fatigue post-call doctors using quantitative electroencephalogram

Introduction . It is common to find doctors working long and odd hours and many at times without rest and sleep. Despite the evidence of adverse risk, patient safety is jeopardised under the hands of fatigue doctors. Such working hours have yet to change in many places. It is argued that with such training and subsequent experience, issues pertaining to patient safety risk reduces. Fatigue too is argued as subjective, as those who can withstand the stress still performs. Nevertheless, undeniably working under fatigue is not safe for both patient and doctor. This study is a novel attempt to explore and objectify the state of fatigue using quantitative EEG among post-call doctors. Methods . Seven volunteer post-call doctors were recruited to go through an EEG recording at rest and subsequently while carrying out a Stroop Test exerting their cognitive function to work. Results . The doctors have worked up to 34 hours in a row and with only an average sleep of 1.5 hours. During the task, there is a statistically significant increase in theta (frontal and occipital regions) and beta (occipital region) band power. Frontal lobe shows an increase in alpha band power but reduced in other regions. The Stroop Test conducted indicated that the speed of answering the congruent trials was faster than the incongruent trials significantly with a slightly more correct result. Conclusion . Frontal increase of theta and alpha band power implies cognitive fatigue. This objectively presents that fatigue doctors are under more strain while carrying out a task and the implicated regions of brain stimulated by the task correspond accordingly.

Human subthalamic oscillatory dynamics following somatosensory stimulation

ObjectiveElectrical median nerve somatosensory stimulation leads to a distinct modulation of cortical oscillations. Initial high frequency and gamma augmentation, as well as modulation of beta and alpha oscillations have been reported. We aimed at investigating the involvement of the subthalamic nucleus in somatosensory processing by means of local field potential recordings, since recordings during passive movements and peripheral somatosensory stimulation have suggested a prominent role. MethodsRecordings of subthalamic neuronal activity following median nerve stimulation in 11 Parkinson’s disease patients were performed. Time-frequency analysis from 1 to 500 Hz was averaged and analyzed. ResultsSeveral oscillatory components in response to somatosensory stimulation were revealed in the time-frequency analysis: (I) prolonged increase in alpha band power, followed by attenuation; (II) initial suppression of power followed by a subsequent rebound in the beta band; (III) early broad-frequency increase in gamma band power; (IV) and sustained increase of 160 Hz frequency oscillations throughout the trial. ConclusionsThese results further corroborate the involvement of the subthalamic nucleus in somatosensory processing. SignificanceThe present results not only support the notion of somatosensory processing in the subthalamic nucleus. Moreover, an improvement of somatosensory processing during subthalamic deep brain stimulation in Parkinson’s disease might be accounted for by enhancement of prevailing high frequency oscillations.

Load-Dependent Increases in Delay-Period Alpha-Band Power Track the Gating of Task-Irrelevant Inputs to Working Memory.

Studies exploring the role of neural oscillations in cognition have revealed sustained increases in alpha-band power (ABP) during the delay period of verbal and visual working memory (VWM) tasks. There have been various proposals regarding the functional significance of such increases, including the inhibition of task-irrelevant cortical areas as well as the active retention of information in VWM. The present study examines the role of delay-period ABP in mediating the effects of interference arising from on-going visual processing during a concurrent VWM task. Specifically, we reasoned that, if set-size dependent increases in ABP represent the gating out of on-going task-irrelevant visual inputs, they should be predictive with respect to some modulation in visual evoked potentials resulting from a task-irrelevant delay period probe stimulus. In order to investigate this possibility, we recorded the electroencephalogram while subjects performed a change detection task requiring the retention of two or four novel shapes. On a portion of trials, a novel, task-irrelevant bilateral checkerboard probe was presented mid-way through the delay. Analyses focused on examining correlations between set-size dependent increases in ABP and changes in the magnitude of the P1, N1 and P3a components of the probe-evoked response and how such increases might be related to behavior. Results revealed that increased delay-period ABP was associated with changes in the amplitude of the N1 and P3a event-related potential (ERP) components, and with load-dependent changes in capacity when the probe was presented during the delay. We conclude that load-dependent increases in ABP likely play a role in supporting short-term retention by gating task-irrelevant sensory inputs and suppressing potential sources of disruptive interference.

Load-Dependent Increases in Alpha-Band Power: Relevance to Sensory Cortex Excitability and Distractor Interference

Load-Dependent Increases in Alpha-Band Power: Relevance to Sensory Cortex Excitability and Distractor Interference

Decreased visual detection during subliminal stimulation.

What is the perceptual fate of invisible stimuli-are they processed at all and does their processing have consequences for the perception of other stimuli? As has been shown previously in the somatosensory system, even stimuli that are too weak to be consciously detected can influence our perception: Subliminal stimulation impairs perception of near-threshold stimuli and causes a functional deactivation in the somatosensory cortex. In a recent study, we showed that subliminal visual stimuli lead to similar responses, indicated by an increase in alpha-band power as measured with electroencephalography (EEG). In the current study, we investigated whether a behavioral inhibitory mechanism also exists within the visual system. We tested the detection of peripheral visual target stimuli under three different conditions: Target stimuli were presented alone or embedded in a concurrent train of subliminal stimuli either at the same location as the target or in the opposite hemifield. Subliminal stimuli were invisible due to their low contrast, not due to a masking procedure. We demonstrate that target detection was impaired by the subliminal stimuli, but only when they were presented at the same location as the target. This finding indicates that subliminal, low-intensity stimuli induce a similar inhibitory effect in the visual system as has been observed in the somatosensory system. In line with previous reports, we propose that the function underlying this effect is the inhibition of spurious noise by the visual system.

OP 12. Effects of transcranial static magnetic field stimulation (tSMS) over the human visual cortex: Behavioural and electrophysiological effects

We previously reported that continuous application of Transcranial Static Magnetic Field Stimulation (tSMS) over the motor cortex induces a reduction of cortical excitability lasting several minutes after the end of tSMS. In the present study, we further explore static magnetic field effects on EEG oscillations in the visual cortex and during visual attentional performance in healthy humans. We specifically test a hypothesis that our previous tSMS effects in motor cortex could be related to an increase of alpha band activity, and therefore, associated with an “inhibitory” effect. Thus, we investigated the effects of tSMS (real or sham) placed over visual cortex in two studies: a first experiment, in which tSMS was simultaneous applied during ten minutes eyes-open resting EEG recording; a second experiment, in which visual attention was measured in the context of tSMS during performance of a visual search paradigm. In both experiments, EEG and behavioural measurements were made during, and 10 min following, tSMS application. As predicted, the application of real, but not sham, tSMS over the visual cortex resulted in a significant increase in alpha band power. In the visual search task, real and sham tSMS groups displayed a similar behavioural profile, with reaction times (RTs) increasing with increasing task demands. Critically, however, a significant slowing of RTs emerged on trials with the highest difficulty levels during real in comparison to sham tSMS . Our results therefore suggest that tSMS has a profound influence on oscillatory alpha activity, which we suggest reflects a modulation of visual cortical excitability. Secondly, our behavioural results indicate that tSMS over the occiput alters visual search performance, slowing responses to stimulus detection. Importantly, this was not a general task impairment, but a tSMS-induced slowing of visual search specific to high attentional load levels. We speculate that this slowing is secondary to a decrease in underlying alpha oscillations. Further studies using tSMS are required to extend the knowledge of the functional significance of brain oscillations changes induced by the application of small magnets over the scalp.

Effect of prestimulus alpha power, phase, and synchronization on stimulus detection rates in a biophysical attractor network model.

Spontaneous oscillations measured by local field potentials, electroencephalograms and magnetoencephalograms exhibit a pronounced peak in the alpha band (8-12 Hz) in humans and primates. Both instantaneous power and phase of these ongoing oscillations have commonly been observed to correlate with psychophysical performance in stimulus detection tasks. We use a novel model-based approach to study the effect of prestimulus oscillations on detection rate. A previously developed biophysically detailed attractor network exhibits spontaneous oscillations in the alpha range before a stimulus is presented and transiently switches to gamma-like oscillations on successful detection. We demonstrate that both phase and power of the ongoing alpha oscillations modulate the probability of such state transitions. The power can either positively or negatively correlate with the detection rate, in agreement with experimental findings, depending on the underlying neural mechanism modulating the oscillatory power. Furthermore, the spatially distributed alpha oscillators of the network can be synchronized by global nonspecific weak excitatory signals. These synchronization events lead to transient increases in alpha-band power and render the network sensitive to the exact timing of target stimuli, making the alpha cycle function as a temporal mask in line with recent experimental observations. Our results are relevant to several studies that attribute a modulatory role to prestimulus alpha dynamics.

Repetitive transcranial magnetic stimulation affects behavior by biasing endogenous cortical oscillations

A governing assumption about repetitive transcranial magnetic stimulation (rTMS) has been that it interferes with task-related neuronal activity – in effect, by “injecting noise” into the brain – and thereby disrupts behavior. Recent reports of rTMS-produced behavioral enhancement, however, call this assumption into question. We investigated the neurophysiological effects of rTMS delivered during the delay period of a visual working memory task by simultaneously recording brain activity with electroencephalography (EEG). Subjects performed visual working memory for locations or for shapes, and in half the trials a 10-Hz train of rTMS was delivered to the superior parietal lobule (SPL) or a control brain area. The wide range of individual differences in the effects of rTMS on task accuracy, from improvement to impairment, was predicted by individual differences in the effect of rTMS on power in the alpha-band of the EEG (∼10 Hz): a decrease in alpha-band power corresponded to improved performance, whereas an increase in alpha-band power corresponded to the opposite. The EEG effect was localized to cortical sources encompassing the frontal eye fields and the intraparietal sulcus, and was specific to task (location, but not object memory) and to rTMS target (SPL, not control area). Furthermore, for the same task condition, rTMS-induced changes in cross-frequency phase synchrony between alpha- and gamma-band (>40 Hz) oscillations predicted changes in behavior. These results suggest that alpha-band oscillations play an active role cognitive processes and do not simply reflect absence of processing. Furthermore, this study shows that the complex effects of rTMS on behavior can result from biasing endogenous patterns of network-level oscillations.

Hjärnans elektriska bakgrunds-aktivitet som mått på kognitiva processer

The short-lasting, event-related amplitude attenuation of the rhythms in EEC alpha band is called event-related desynchronization (ERD). The opposite phenomenon, event-related synchronization (ERS) is the phasic increase in alpha band power. The alpha rhythm of the EEG is characteristic for inactive cortical fields and alpha desynchronization is thus an indicator of cortical activation. This paper discusses recent findings on the ERD/ERS phenomenon in the auditory stimulus modality. Results on ERD/ERS studies, in which complex auditory stimulation has been examined, are presented and discussed from a theoretical framework. The ERD/ERS technique is likely to be an intriguing method for studying brain electric activation patterns related to higher cognitive functions, such as attention and memory, as well as deviances in these functions.

Cerebral activity prior to motion task performance: An electroencephalographic study

Cerebral activity, as reflected by power in the alpha waveband (8-13 Hz), was examined prior to the performance of three tasks with different effort and accuracy requirements. The study aimed to further investigate changes in activity observed in an earlier study in which expert karate performers exhibited significant increases in alpha band power during preparation for a training task. In contrast to the earlier research, the high effort task produced a significant decrease in 'alpha' power prior to performance. 'Alpha' power prior to the high accuracy task showed significant differences mediated by the outcome. Successful performance was preceded by higher levels of 'alpha' power than unsuccessful attempts. The reported use of a cognitive strategy on the first task produced a significant difference in activity, lower alpha power being associated with the use of such a technique.