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The influence of transcranial alternating current stimulation (tACS) on fluid intelligence: An fMRI study.

ABSTRACT: The past decades have witnessed a huge interest in uncovering the neural bases of intelligence (e.g., Stelmack, & Houlihan, 1995; Stelmack, Knott, & Beauchamp, 2003). This study investigated the influence of transcranial alternating current stimulation (tACS) on fluid intelligence performance and corresponding brain activation. Previous findings showed that left parietal theta tACS leads to a transient increase in fluid reasoning performance. In an attempt to extend and replicate these findings, we combined theta tACS with fMRI. In a double-blind sham-controlled experiment, N = 20 participants worked on two intelligence tasks (matrices and paper folding) after theta tACS was applied to the left parietal cortex. Stimulation-induced brain activation changes were recorded during task processing using fMRI. Results showed that theta tACS significantly increased fluid intelligence performance when working on difficult items in the matrices test; no effect was observed for the visuo-spatial paper folding test. Whole-brain analyses showed that left parietal brain stimulation was accompanied by lower activation in task-irrelevant brain areas. Complemental ROI analyses revealed a tendency towards lower activation in the left inferior parietal cortex. These findings corroborate the functional role of left parietal theta activity in fluid reasoning and are in line with the neural efficiency hypothesis.

SUBMITTER: Neubauer AC

PROVIDER: S-EPMC5700801 | biostudies-literature | 2017 Nov

REPOSITORIES: biostudies-literature

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The influence of transcranial alternating current stimulation (tACS) on fluid intelligence: An fMRI study.

Neubauer A C AC Wammerl M M Benedek M M Jauk E E Jaušovec N N

Personality and individual differences 20171101

The past decades have witnessed a huge interest in uncovering the neural bases of intelligence (e.g., Stelmack, & Houlihan, 1995; Stelmack, Knott, & Beauchamp, 2003). This study investigated the influence of transcranial alternating current stimulation (tACS) on fluid intelligence performance and corresponding brain activation. Previous findings showed that left parietal theta tACS leads to a transient increase in fluid reasoning performance. In an attempt to extend and replicate these findings, ...[more]

PMID: 29176918

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Project description:BackgroundOver 55 million people worldwide are currently diagnosed with Alzheimer's disease (AD) and live with debilitating episodic memory deficits. Current pharmacological treatments have limited efficacy. Recently, transcranial alternating current stimulation (tACS) has shown memory improvement in AD by normalizing high-frequency neuronal activity. Here we investigate the feasibility, safety, and preliminary effects on episodic memory of an innovative protocol where tACS is administered within the homes of older adults with AD with the help of a study companion (HB-tACS).MethodsEight participants diagnosed with AD underwent multiple consecutive sessions of high-definition HB-tACS (40 Hz, 20-min) targeting the left angular gyrus (AG), a key node of the memory network. The Acute Phase comprised 14-weeks of HB-tACS with at least five sessions per week. Three participants underwent resting state electroencephalography (EEG) before and after the 14-week Acute Phase. Subsequently, participants completed a 2-3-month Hiatus Phase not receiving HB-tACS. Finally, in the Taper phase, participants received 2-3 sessions per week over 3-months. Primary outcomes were safety, as determined by the reporting of side effects and adverse events, and feasibility, as determined by adherence and compliance with the study protocol. Primary clinical outcomes were memory and global cognition, measured with the Memory Index Score (MIS) and Montreal Cognitive Assessment (MoCA), respectively. Secondary outcome was EEG theta/gamma ratio. Results reported as mean ± SD.ResultsAll participants completed the study, with an average of 97 HB-tACS sessions completed by each participant; reporting mild side effects during 25% of sessions, moderate during 5%, and severe during 1%. Acute Phase adherence was 98 ± 6.8% and Taper phase was 125 ± 22.3% (rates over 100% indicates participants completed more than the minimum of 2/week). After the Acute Phase, all participants showed memory improvement, MIS of 7.25 ± 3.77, sustained during Hiatus 7.00 ± 4.90 and Taper 4.63 ± 2.39 Phases compared to baseline. For the three participants that underwent EEG, a decreased theta/gamma ratio in AG was observed. Conversely, participants did not show improvement in the MoCA, 1.13 ± 3.80 after the Acute Phase, and there was a modest decrease during the Hiatus -0.64 ± 3.28 and Taper -2.56 ± 5.03 Phases.ConclusionThis pilot study shows that the home-based, remotely-supervised, study companion administered, multi-channel tACS protocol for older adults with AD was feasible and safe. Further, targeting the left AG, memory in this sample was improved. These are preliminary results that warrant larger more definite trials to further elucidate tolerability and efficacy of the HB-tACS intervention. NCT04783350.Clinical trial registrationhttps://clinicaltrials.gov/ct2/show/NCT04783350?term=NCT04783350&draw=2&rank=1, identifier NCT04783350.

Project description:Brain oscillations, e.g. measured by electro- or magnetoencephalography (EEG/MEG), are causally linked to brain functions that are fundamental for perception, cognition and learning. Recent advances in neurotechnology provide means to non-invasively target these oscillations using frequency-tuned amplitude-modulated transcranial alternating current stimulation (AM-tACS). However, online adaptation of stimulation parameters to ongoing brain oscillations remains an unsolved problem due to stimulation artifacts that impede such adaptation, particularly at the target frequency. Here, we introduce a real-time compatible artifact rejection algorithm (Stimulation Artifact Source Separation, SASS) that overcomes this limitation. SASS is a spatial filter (linear projection) removing EEG signal components that are maximally different in the presence versus absence of stimulation. This enables the reliable removal of stimulation-specific signal components, while leaving physiological signal components unaffected. For validation of SASS, we evoked brain activity with known phase and amplitude using 10 Hz visual flickers across 7 healthy human volunteers. 64-channel EEG was recorded during and in absence of 10 Hz AM-tACS targeting the visual cortex. Phase differences between AM-tACS and the visual stimuli were randomized, so that steady-state visually evoked potentials (SSVEPs) were phase-locked to the visual stimuli but not to the AM-tACS signal. For validation, distributions of single-trial amplitude and phase of EEG signals recorded during and in absence of AM-tACS were compared for each participant. When no artifact rejection method was applied, AM-tACS stimulation artifacts impeded assessment of single-trial SSVEP amplitude and phase. Using SASS, amplitude and phase of single trials recorded during and in absence of AM-tACS were comparable. These results indicate that SASS can be used to establish adaptive (closed-loop) AM-tACS, a potentially powerful tool to target various brain functions, and to investigate how AM-tACS interacts with electric brain oscillations.

Project description:Objective: To determine whether remotely-monitored transcranial alternating current stimulation (tACS) may be a viable and safe treatment option for Mal de Débarquement Syndrome (MdDS). Background: Mal de Débarquement Syndrome is a neurotological disorder characterized by persistent oscillating vertigo that is triggered by entrainment to passive oscillatory motion such as occurs during water-based travel. Treatment options for MdDS are limited, variably effective, and can be undone by further travel. Design and Methods: This was a remotely-monitored open-label optional extension phase of a double-blind randomized onsite study of tACS for medically refractory MdDS. The primary goal was to determine safety, feasibility, and blinded participant feedback. The secondary goal was to determine efficacy. Thirteen participants (all women), aged 22-67 years, experiencing a duration of illness of 11-72 months, were a subset of 24 individuals who participated in an on-site study of tACS. They had either not responded to the on-site protocol or had relapsed after travel home. Treatment accessories and a tablet controlled tACS stimulator (Pulvinar XCSITE-100) were mailed to participants. Three teaching sessions were performed via webcam followed by on-going remote monitoring of treatment logs and participants' reports through a daily on-line diary and weekly questionnaires. Treatment continued until an effective protocol was administered for 4 weeks and then tapered over 4 weeks. Participants completed a blinded feedback survey and a debriefing interview at the completion of the entire study. Results: Treatment duration ranged from 4 to 31 weeks followed by a 4-week taper accounting for 578 verified sessions. Of the 13 total participants, seven agreed or agreed strongly in the blinded survey that tACS treatment was beneficial; 2) Twelve were comfortable utilizing tACS on their own; 3) Eleven preferred stimulation above their individual alpha frequency; 4) Side effects were generally mild and typical of tACS. In the debriefing interview completed 2-9 months after the last stimulation, five participants reported doing "great," with no to minimal symptoms, four reported doing "good," with moderate symptoms, and four reported no change compared to pre-study baseline. Conclusion: Remotely-monitored tACS may be a safe treatment option for MdDS with the potential for lasting outcomes, increased accessibility, and reduction in travel-related treatment reversal.

Project description:Motor control is associated with synchronized oscillatory activity at alpha (8-12 Hz) and beta (12-30 Hz) frequencies in a cerebello-thalamo-cortical network. Previous studies demonstrated that transcranial alternating current stimulation (tACS) is capable of entraining ongoing oscillatory activity while also modulating motor control. However, the modulatory effects of tACS on both motor control and its underlying electro- and neurophysiological mechanisms remain ambiguous. Thus, the purpose of this study was to contribute to gathering neurophysiological knowledge regarding tACS effects by investigating the after-effects of 10 Hz tACS and 20 Hz tACS at parietal brain areas on bimanual coordination and its concurrent oscillatory and hemodynamic activity. Twenty-four right-handed healthy volunteers (12 females) aged between 18 and 30 (M = 22.35 ± 3.62) participated in the study and performed a coordination task requiring bimanual movements. Concurrent to bimanual motor training, participants received either 10 Hz tACS, 20 Hz tACS or a sham stimulation over the parietal cortex (at P3/P4 electrode positions) for 20 min via small gel electrodes (3,14 cm2 Ag/AgCl, amperage = 1 mA). Before and three time-points after tACS (immediately, 30 min and 1 day), bimanual coordination performance was assessed. Oscillatory activities were measured by electroencephalography (EEG) and hemodynamic changes were examined using functional near-infrared spectroscopy (fNIRS). Improvements of bimanual coordination performance were not differently between groups, thus, no tACS-specific effect on bimanual coordination performance emerged. However, physiological measures during the task revealed significant increases in parietal alpha activity immediately following 10 Hz tACS and 20 Hz tACS which were accompanied by significant decreases of Hboxy concentration in the right hemispheric motor cortex compared to the sham group. Based on the physiological responses, we conclude that tACS applied at parietal brain areas provoked electrophysiological and hemodynamic changes at brain regions of the motor network which are relevant for bimanual motor behavior. The existence of neurophysiological alterations immediately following tACS, especially in the absence of behavioral effects, are elementary for a profound understanding of the mechanisms underlying tACS. The lack of behavioral modifications strengthens the need for further research on tACS effects on neurophysiology and behavior using combined electrophysiological and neuroimaging methods.

Project description:BackgroundClassically, studies adopting non-invasive transcranial electrical stimulation have placed greater importance on the position of the primary "stimulating" electrode than the secondary "reference" electrode. However, recent current density modeling suggests that ascribing a neutral role to the reference electrode may prove an inappropriate oversimplification.HypothesisWe set out to test the hypothesis that the behavioral effects of transcranial electrical stimulation are critically dependent on the position of the return ("reference") electrode.MethodsWe examined the effect of transcranial alternating current stimulation (sinusoidal waveform with no direct current offset at a peak-to-peak amplitude of 2000 μA and a frequency matched to each participant's peak tremor frequency) on physiological tremor in a group of healthy volunteers (N = 12). We implemented a sham-controlled experimental protocol where the position of the stimulating electrode remained fixed, overlying primary motor cortex, whilst the position of the return electrode varied between two cephalic (fronto-orbital and contralateral primary motor cortex) and two extracephalic (ipsilateral and contralateral shoulder) locations. We additionally controlled for the role of phosphenes in influencing motor output by assessing the response of tremor to photic stimulation, through self-reported phosphene ratings.ResultsAltering only the position of the return electrode had a profound behavioral effect: only the montage with extracephalic return contralateral to the primary stimulating electrode significantly entrained physiological tremor (15.9% ± 6.1% increase in phase stability, 1 S.E.M.). Photic stimulation also entrained tremor (11.7% ± 5.1% increase in phase stability). Furthermore, the effects of electrical stimulation are distinct from those produced from direct phosphene induction, in that the latter were only seen with the fronto-orbital montage that did not affect the tremor.ConclusionThe behavioral effects of transcranial alternating current stimulation appear to be critically dependent on the position of the reference electrode, highlighting the importance of electrode montage when designing experimental and therapeutic protocols.

Dataset Information

The influence of transcranial alternating current stimulation (tACS) on fluid intelligence: An fMRI study.

Publications

The influence of transcranial alternating current stimulation (tACS) on fluid intelligence: An fMRI study.

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