Offline 20 Hz transcranial alternating current stimulation over the right inferior frontal gyrus increases theta activity during a motor response inhibition task.

OBJECTIVES: Previous studies have shown that the right inferior frontal gyrus (rIFG) and the pre-supplementary motor area (preSMA) play an important role in motor inhibitory control. The aim of the study was to use theta frequency transcranial alternating current stimulation (tACS) to modulate brain activity in the rIFG and preSMA and to test the effects of stimulation using a motor response inhibition task. METHODS: In four sessions, 20 healthy participants received tACS at 6 Hz over preSMA or rIFG, or 20 Hz over rIFG (to test frequency specificity), or sham stimulation before task processing. After each type of stimulation, the participants performed the Go/NoGo task with simultaneous electroencephalogram (EEG) recording. RESULTS: By stimulating rIFG and preSMA with 6 Hz tACS, we were not able to modulate either behavioral performance nor the EEG correlate. Interestingly, 20 Hz tACS over the rIFG significantly increased theta activity, however without behavioral effects. This increased theta activity did not coincide with the stimulation area and was localized in the fronto-central and centro-parietal areas. CONCLUSIONS: The inclusion of a control frequency is crucial to test for frequency specificity. Our findings are in accordance with previous studies showing that after effects of tACS are not restricted to the stimulation frequency but can also occur in other frequency bands.

Neuronal networks underlying ictal and subclinical discharges in childhood absence epilepsy.

Childhood absence epilepsy (CAE), involves 3 Hz generalized spikes and waves discharges (GSWDs) on the electroencephalogram (EEG), associated with ictal discharges (seizures) with clinical symptoms and impairment of consciousness and subclinical discharges without any objective clinical symptoms or impairment of consciousness. This study aims to comparatively characterize neuronal networks underlying absence seizures and subclinical discharges, using source localization and functional connectivity (FC), to better understand the pathophysiological mechanism of these discharges. Routine EEG data from 12 CAE patients, consisting of 45 ictal and 42 subclinical discharges were selected. Source localization was performed using the exact low-resolution electromagnetic tomography (eLORETA) algorithm, followed by FC based on the imaginary part of coherency. FC based on the thalamus as the seed of interest showed significant differences between ictal and subclinical GSWDs (p < 0.05). For delta (1-3 Hz) and alpha bands (8-12 Hz), the thalamus displayed stronger connectivity towards other brain regions for ictal GSWDs as compared to subclinical GSWDs. For delta band, the thalamus was strongly connected to the posterior cingulate cortex (PCC), precuneus, angular gyrus, supramarginal gyrus, parietal superior, and occipital mid-region for ictal GSWDs. The strong connections of the thalamus with other brain regions that are important for consciousness, and with components of the default mode network (DMN) suggest the severe impairment of consciousness in ictal GSWDs. However, for subclinical discharges, weaker connectivity between the thalamus and these brain regions may suggest the prevention of impairment of consciousness. This may benefit future therapeutic targets and improve the management of CAE patients.

Differentiating ictal/subclinical spikes and waves in childhood absence epilepsy by spectral and network analyses: A pilot study.

OBJECTIVE: Childhood absence epilepsy (CAE) is a disease with distinct seizure semiology and electroencephalographic (EEG) features. Differentiating ictal and subclinical generalized spikes and waves discharges (GSWDs) in the EEG is challenging, since they appear to be identical upon visual inspection. Here, spectral and functional connectivity (FC) analyses were applied to routine EEG data of CAE patients, to differentiate ictal and subclinical GSWDs. METHODS: Twelve CAE patients with both ictal and subclinical GSWDs were retrospectively selected for this study. The selected EEG epochs were subjected to frequency analysis in the range of 1-30 Hz. Further, FC analysis based on the imaginary part of coherency was used to determine sensor level networks. RESULTS: Delta, alpha and beta band frequencies during ictal GSWDs showed significantly higher power compared to subclinical GSWDs. FC showed significant network differences for all frequency bands, demonstrating weaker connectivity between channels during ictal GSWDs. CONCLUSION: Using spectral and FC analyses significant differences between ictal and subclinical GSWDs in CAE patients were detected, suggesting that these features could be used for machine learning classification purposes to improve EEG monitoring. SIGNIFICANCE: Identifying differences between ictal and subclinical GSWDs using routine EEG, may improve understanding of this syndrome and the management of patients with CAE.

Significance of Beta-Band Oscillations in Autism Spectrum Disorders During Motor Response Inhibition Tasks: A MEG Study.

In Autism Spectrum Disorders (ASD), impaired response inhibition and lack of adaptation are hypothesized to underlie core ASD symptoms, such as social communication and repetitive, stereotyped behavior. Thus, the aim of the present study was to compare neural correlates of inhibition, post-error adaptation, and reaction time variability in ASD and neuro-typical control (NTC) participants by investigating possible differences in error-related changes of oscillatory MEG activity. Twelve male NTC (mean age 20.3 ± 3.7) and fourteen male patients with ASD (mean age 17.8 ± 2.9) were included in the analysis. Subjects with ASD showed increased error-related reaction time variability. MEG analysis revealed decreased beta power in the ASD group in comparison to the NTC group over the centro-parietal channels in both, the pre-stimulus and post-response interval. In the ASD group, mean centro-parietal beta power negatively correlated with dimensional autism symptoms. In both groups, false alarms were followed by an early increase in temporo-frontal theta to alpha power; and by a later decrease in alpha to beta power at central and posterior sensors. Single trial correlations were additionally studied in the ASD group, who showed a positive correlation of pre-stimulus beta power with post-response theta, alpha, and beta power, particularly after hit trials. On a broader scale, the results deliver important insights into top-down control deficits that may relate to core symptoms observed in ASD.

After-effects of 10 Hz tACS over the prefrontal cortex on phonological word decisions.

INTRODUCTION: Previous work in the language domain has shown that 10 Hz rTMS of the left or right posterior inferior frontal gyrus (pIFG) in the prefrontal cortex impaired phonological decision-making, arguing for a causal contribution of the bilateral pIFG to phonological processing. However, the neurophysiological correlates of these effects are unclear. The present study addressed the question whether neural activity in the prefrontal cortex could be modulated by 10 Hz tACS and how this would affect phonological decisions. METHODS: In three sessions, 24 healthy participants received tACS at 10 Hz or 16.18 Hz (control frequency) or sham stimulation over the bilateral prefrontal cortex before task processing. Resting state EEG was recorded before and after tACS. We also recorded EEG during task processing. RESULTS: Relative to sham stimulation, 10 Hz tACS significantly facilitated phonological response speed. This effect was task-specific as tACS did not affect a simple control task. Moreover, 10 Hz tACS significantly increased theta power during phonological decisions. The individual increase in theta power was positively correlated with the behavioral facilitation after 10 Hz tACS. CONCLUSION: Our results show a facilitation of phonological decisions after 10 Hz tACS over the bilateral prefrontal cortex. This might indicate that 10 Hz tACS increased task-related activity in the stimulated area to a level that was optimal for phonological performance. The significant correlation with the individual increase in theta power suggests that the behavioral facilitation might be related to increased theta power during language processing.

1 mA cathodal tDCS shows excitatory effects in children and adolescents: Insights from TMS evoked N100 potential.

In children and adolescents, 1 mA transcranial direct current stimulation (tDCS) may cause "paradoxical" effects compared with adults: both 1 mA anodal and cathodal tDCS increase amplitude of the motor evoked potential (MEP) as revealed by a single pulse transcranial magnetic stimulation (TMS) of the motor cortex. Here, EEG based evoked potentials induced by a single pulse TMS, particularly the N100 component as marker of motor cortex inhibition, were investigated in order to explain effects of tDCS on the developing brain. In nineteen children and adolescents (11-16 years old), 1 mA anodal, cathodal, or sham tDCS was applied over the left primary motor cortex for 10 min. The TMS-evoked N100 was measured by 64-channel EEG before and immediately after stimulation as well as every 10 min after tDCS for one hour. 1 mA Cathodal stimulation suppressed the N100 amplitude compared with sham stimulation. In contrast, anodal tDCS did not modify the N100 amplitude. It seems likely that the increase of the motor cortex activity under cathodal tDCS in children and adolescents as shown in previous studies can be attributed to a reduce inhibition. Based on TMS evoked N100, the study provides an insight into neuromodulatory effects of tDCS on the developing brain.

Ten minutes of 1 mA transcranial direct current stimulation was well tolerated by children and adolescents: Self-reports and resting state EEG analysis.

Transcranial direct current stimulation (tDCS) is a promising and well-tolerated method of non-invasive brain stimulation, by which cortical excitability can be modulated. However, the effects of tDCS on the developing brain are still unknown, and knowledge about its tolerability in children and adolescents is still lacking. Safety and tolerability of tDCS was assessed in children and adolescents by self-reports and spectral characteristics of electroencephalogram (EEG) recordings. Nineteen typically developing children and adolescents aged 11-16 years participated in the study. Anodal and cathodal tDCS as well as sham stimulation were applied for a duration of 10 min over the left primary motor cortex (M1), each with an intensity of 1 mA. Subjects were unable to identify whether they had received active or sham stimulation, and all participants tolerated the stimulation well with a low rate of adverse events in both groups and no serious adverse events. No pathological oscillations, in particular, no markers of epileptiform activity after 1mA tDCS were detected in any of the EEG analyses. In summary, our study demonstrates that tDCS with 1mA intensity over 10 min is well tolerated, and thus may be used as an experimental and treatment method in the pediatric population.

Stimulation intensities of transcranial direct current stimulation have to be adjusted in children and adolescents.

OBJECTIVE: The aim of the present study was to investigate the effect of the transcranial direct current stimulation (tDCS) on motor cortex excitability in healthy children and adolescents. METHODS: We applied 1mA anodal or cathodal tDCS for 10min on the left primary motor cortex of 19 healthy children and adolescents (mean age 13.9±0.4years). In order to prove whether the effects of tDCS may be attributed to the stimulation intensity, 10 children and adolescents were studied again using 0.5mA anodal and cathodal tDCS. Sham stimulation was used as a control. RESULTS: Compared with sham stimulation, both 1mA anodal and cathodal tDCS resulted in a significant increase of Motor evoked potentials (MEP) amplitudes which remained to be prominent even one hour after the end of stimulation. Interestingly, the 0.5mA cathodal tDCS decreased cortico-spinal excitability whereas the 0.5mA anodal stimulation did not result in any effect. CONCLUSION: For the first time, the study demonstrates age-specific influences of tDCS on cortical excitability of the primary motor cortex. SIGNIFICANCE: Thus, the stimulation protocols of the tDCS have to be optimized according to age by planning studies in pediatric population.