scholarly journals Modulation of large-scale cortical coupling by transcranial alternating current stimulation

2018 ◽  
Author(s):  
Bettina C. Schwab ◽  
Jonas Misselhorn ◽  
Andreas K. Engel
Keyword(s):  
Functional Connectivity ◽  
Long Range ◽  
Electric Fields ◽  
Large Scale ◽  
Alternating Current ◽  
Total Power ◽  
Maximum Effect ◽  
High Definition ◽  
Transcranial Alternating Current Stimulation ◽  
Eeg Connectivity

AbstractBackgroundLong-range functional connectivity in the brain is considered fundamental for cognition and is known to be altered in many neuropsychiatric disorders. To modify such coupling independent of sensory input, noninvasive brain stimulation could be of utmost value.ObjectiveFirst, we tested if transcranial alternating current stimulation (tACS) is able to influence functional connectivity in the human brain. Second, we investigated the specificity of effects in frequency and space.MethodsEEG aftereffects of bifocal high-definition tACS were analyzed systematically in sensor and source space. Participants were stimulated transcranially in counterbalanced order (1) in-phase, with identical electric fields in both hemispheres, (2) anti-phase, with phase-reversed electric fields in the two hemispheres, and (3) jittered-phase, generated by subtle frequency shifts continuously changing the phase relation between the two fields.ResultsWhile total power and spatial distribution of the fields were comparable between conditions, global pre-post stimulation changes in EEG connectivity were larger after in-phase stimulation than after anti-phase or jittered-phase stimulation. Those differences in connectivity were restricted to the stimulated frequency band and decayed within the first 120 s after stimulation offset. Source reconstruction localized the maximum effect between the stimulated occipitoparietal areas.ConclusionThe relative phase of bifocal alpha-tACS modulated alpha-band connectivity between the targeted regions. As side effects did not differ between stimulation conditions, we conclude that neural activity was phase-specifically influenced by the electric fields. We thus suggest bifocal high-definition tACS as a tool to manipulate long-range cortico-cortical coupling which outlasts the stimulation period.

scholarly journals Transcranial alternating current stimulation attenuates BOLD adaptation and increases functional connectivity

2020 ◽  
Vol 123 (1) ◽  
pp. 428-438 ◽  
Author(s):  
Kohitij Kar ◽  
Takuya Ito ◽  
Michael W. Cole ◽  
Bart Krekelberg
Keyword(s):  
Functional Connectivity ◽  
Electric Fields ◽  
Full Range ◽  
Region Of Interest ◽  
Alternating Current ◽  
Human Motion ◽  
Dependent Manner ◽  
Bold Imaging ◽  
Transcranial Alternating Current Stimulation ◽  
The Brain

Transcranial alternating current stimulation (tACS) is used as a noninvasive tool for cognitive enhancement and clinical applications. The physiological effects of tACS, however, are complex and poorly understood. Most studies of tACS focus on its ability to entrain brain oscillations, but our behavioral results in humans and extracellular recordings in nonhuman primates support the view that tACS at 10 Hz also affects brain function by reducing sensory adaptation. Our primary goal in the present study is to test this hypothesis using blood oxygen level-dependent (BOLD) imaging in human subjects. Using concurrent functional magnetic resonance imaging (fMRI) and tACS, and a motion adaptation paradigm developed to quantify BOLD adaptation, we show that tACS significantly attenuates adaptation in the human motion area (hMT+). In addition, an exploratory analysis shows that tACS increases functional connectivity of the stimulated hMT+ with the rest of the brain and the dorsal attention network in particular. Based on field estimates from individualized head models, we relate these changes to the strength of tACS-induced electric fields. Specifically, we report that functional connectivity (between hMT+ and any other region of interest) increases in proportion to the field strength in the region of interest. These findings add support for the claim that weak 10-Hz currents applied to the scalp modulate both local and global measures of brain activity. NEW & NOTEWORTHY Concurrent transcranial alternating current stimulation (tACS) and functional MRI show that tACS affects the human brain by attenuating adaptation and increasing functional connectivity in a dose-dependent manner. This work is important for our basic understanding of what tACS does, but also for therapeutic applications, which need insight into the full range of ways in which tACS affects the brain.

scholarly journals Transcranial Alternating Current Stimulation (tACS) Entrains Alpha Oscillations by Preferential Phase Synchronization of Fast-Spiking Cortical Neurons to Stimulation Waveform

2019 ◽  
Author(s):  
Ehsan Negahbani ◽  
Iain M. Stitt ◽  
Marshall Davey ◽  
Thien T. Doan ◽  
Moritz Dannhauer ◽  
...  
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Cortical Neurons ◽  
Posterior Parietal Cortex ◽  
Phase Synchronization ◽  
Alternating Current ◽  
Arnold Tongue ◽  
Transcranial Alternating Current Stimulation ◽  
Neuronal Oscillators

SummaryModeling studies predict that transcranial alternating current stimulation (tACS) entrains brain oscillations, yet direct examination has been lacking or potentially contaminated by stimulation artefact. Here we first demonstrate how the posterior parietal cortex drives primary visual cortex and thalamic LP in the alpha-band in head-fixed awake ferrets. The spike-field synchrony is maximum within alpha frequency, and more prominent for narrow-spiking neurons than broad-spiking ones. Guided by a validated model of electric field distribution, we produced electric fields comparable to those in humans and primates (< 0.5 mV/mm). We found evidence to support the model-driven predictions of how tACS entrains neural oscillations as explained by the triangular Arnold tongue pattern. In agreement with the stronger spike-field coupling of narrow-spiking cells, tACS more strongly entrained this cell population. Our findings provide the firstin vivoevidence of how tACS with electric field amplitudes used in human studies entrains neuronal oscillators.

scholarly journals Endogenous and exogenous electric fields as modifiers of brain activity: rational design of noninvasive brain stimulation with transcranial alternating current stimulation

2014 ◽  
Vol 16 (1) ◽  
pp. 93-102 ◽  
Keyword(s):  
Electric Fields ◽  
Brain Stimulation ◽  
Rational Design ◽  
Brain Activity ◽  
Field Potential ◽  
Alternating Current ◽  
Noninvasive Brain Stimulation ◽  
Starting Point ◽  
Recent Developments ◽  
Transcranial Alternating Current Stimulation

Synchronized neuronal activity in the cortex generates weak electric fields that are routinely measured in humans and animal models by electroencephalography and local field potential recordings. Traditionally, these endogenous electric fields have been considered to be an epiphenomenon of brain activity. Recent work has demonstrated that active cortical networks are surprisingly susceptible to weak perturbations of the membrane voltage of a large number of neurons by electric fields. Simultaneously, noninvasive brain stimulation with weak, exogenous electric fields (transcranial current stimulation, TCS) has undergone a renaissance due to the broad scope of its possible applications in modulating brain activity for cognitive enhancement and treatment of brain disorders. This review aims to interface the recent developments in the study of both endogenous and exogenous electric fields, with a particular focus on rhythmic stimulation for the modulation of cortical oscillations. The main goal is to provide a starting point for the use of rational design for the development of novel mechanism-based TCS therapeutics based on transcranial alternating current stimulation, for the treatment of psychiatric illnesses.

scholarly journals Evaluation of a Modified High-Definition Electrode Montage for Transcranial Alternating Current Stimulation (tACS) of Pre-Central Areas

2016 ◽  
Vol 9 (5) ◽  
pp. 700-704 ◽  
Author(s):  
Kirstin-Friederike Heise ◽  
Nick Kortzorg ◽  
Guilherme Bicalho Saturnino ◽  
Hakuei Fujiyama ◽  
Koen Cuypers ◽  
...  
Keyword(s):  
Alternating Current ◽  
High Definition ◽  
Transcranial Alternating Current Stimulation

scholarly journals Dose-Dependent Effects of Transcranial Alternating Current Stimulation on Spike Timing in Awake Nonhuman Primates

2019 ◽  
Author(s):  
Luke Johnson ◽  
Ivan Alekseichuk ◽  
Jordan Krieg ◽  
Alex Doyle ◽  
Ying Yu ◽  
...  
Keyword(s):  
Electric Fields ◽  
Nonhuman Primates ◽  
Brain Activity ◽  
Alternating Current ◽  
Spike Timing ◽  
Novel Treatments ◽  
Dose Dependent Fashion ◽  
Transcranial Alternating Current Stimulation ◽  
Dose Dependent

ABSTRACTWeak extracellular electric fields can influence spike timing in neural networks. Approaches to impose such fields on the brain in a noninvasive manner have high potential for novel treatments of neurological and psychiatric disorders. One of these methods, transcranial alternating current stimulation (TACS), is hypothesized to affect spike timing and cause neural entrainment. However, the conditions under which these effects occur in-vivo are unknown. Here, we show that TACS modulates spike timing in awake nonhuman primates (NHPs) in a dose-dependent fashion. Recording single-unit activity from pre-and post-central gyrus regions in NHPs during TACS, we found that a larger population of neurons became entrained to the stimulation waveform for higher stimulation intensities. Performing a cluster analysis of changes in interspike intervals, we identified two main types of neural responses to TACS – increased burstiness and phase entrainment. Our results demonstrate the ability of TACS to affect spike-timing in the awake primate brain and identify fundamental neural mechanisms. Concurrent electric field recordings demonstrate that spike-timing changes occur with stimulation intensities readily achievable in humans. These results suggest that novel TACS protocols tailored to ongoing brain activity may be a potent tool to normalize spike-timing in maladaptive brain networks and neurological disease.

scholarly journals Removal of Gross Artifacts of Transcranial Alternating Current Stimulation in Simultaneous EEG Monitoring

Sensors ◽  
2019 ◽  
Vol 19 (1) ◽  
pp. 190 ◽  
Author(s):  
Siddharth Kohli ◽  
Alexander J. Casson
Keyword(s):  
Large Scale ◽  
Alternating Current ◽  
Event Related Potential ◽  
Transcranial Electrical Stimulation ◽  
Trade Offs ◽  
Multi Stage ◽  
Before And After ◽  
Transcranial Alternating Current Stimulation ◽  
Eeg Recordings ◽  
The Time Domain

Transcranial electrical stimulation is a widely used non-invasive brain stimulation approach. To date, EEG has been used to evaluate the effect of transcranial Direct Current Stimulation (tDCS) and transcranial Alternating Current Stimulation (tACS), but most studies have been limited to exploring changes in EEG before and after stimulation due to the presence of stimulation artifacts in the EEG data. This paper presents two different algorithms for removing the gross tACS artifact from simultaneous EEG recordings. These give different trade-offs in removal performance, in the amount of data required, and in their suitability for closed loop systems. Superposition of Moving Averages and Adaptive Filtering techniques are investigated, with significant emphasis on verification. We present head phantom testing results for controlled analysis, together with on-person EEG recordings in the time domain, frequency domain, and Event Related Potential (ERP) domain. The results show that EEG during tACS can be recovered free of large scale stimulation artifacts. Previous studies have not quantified the performance of the tACS artifact removal procedures, instead focusing on the removal of second order artifacts such as respiration related oscillations. We focus on the unresolved challenge of removing the first order stimulation artifact, presented with a new multi-stage validation strategy.

scholarly journals Reduction of somatosensory functional connectivity by transcranial alternating current stimulation at endogenous mu-frequency

NeuroImage ◽  
2020 ◽  
Vol 221 ◽  
pp. 117175
Author(s):  
Christopher Gundlach ◽  
Matthias M. Müller ◽  
Maike Hoff ◽  
Patrick Ragert ◽  
Till Nierhaus ◽  
...  
Keyword(s):  
Functional Connectivity ◽  
Alternating Current ◽  
Transcranial Alternating Current Stimulation
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