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Coldea, Andra, Stephanie Morand, Domenica Veniero, Monika Harvey, and Gregor Thut. 2021. ‘Parietal alpha tACS shows inconsistent effects on visuospatial attention’, Plos one, 16(8).
Summary: In the literature, alpha-tACS has been shown to shift attention away from the contralateral towards the ipsilateral visual field. During this replication study, Coldea et al. applied left parietal alpha-tACS (10 Hz) during an attentional task and found no changes in task performance or resting-state EEG with respect to sham. The authors call for more tACS replication studies to understand the factors that contribute to tACS efficacy, such as stimulation intensity and duration. Although numerous studies have used tACS to successfully modulate neural oscillations and behavior, it is equally important to carefully consider studies, such as this one, that demonstrate limits of tACS. Pros: ● Included resting-state EEG immediately following stimulation to account for artifacts present during stimulation ● Successful blinding of participants to alpha-tACS vs sham ● Use of an attentional task where tACS successfully modulated performance in a past study Open questions: ● How do tACS intensity and stimulation duration change effects? ● Does individualized peak frequency alpha-tACS enhance effects? ●Are there changes in EEG during the task which are obscured by the extensive artifacts introduced with stimulation? ●Would accuracy changes with alpha-tACS have been found if participants had not performed so close to ceiling (average accuracy of 95%)? Contributed by: Amber McFerren
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Alekseichuk, Ivan, Zsolt Turi, Gabriel Amador de Lara, Andrea Antal, and Walter Paulus. 2016. 'Spatial working memory in humans depends on theta and high gamma synchronization in the prefrontal cortex', Current Biology, 26: 1513-21.
Summary: Slow frequency neural oscillations couple to higher frequency neural oscillations during tasks that require cognitive control. Alekseichuk et al. use a novel approach to customize the waveform of tACS to mimic the cross-frequency coupling pattern. Using a high-definition electrode montage to target left prefrontal cortex, cross-frequency tACS was delivered as participants performed a spatial working memory task. Cross-frequency tACS increased behavior performance. Pros:
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Contributed by: Justin Riddle, PhD Polanía, Rafael, Michael A Nitsche, Carolin Korman, Giorgi Batsikadze, and Walter Paulus. 2012. 'The importance of timing in segregated theta phase-coupling for cognitive performance', Current Biology, 22: 1314-18.
Summary: Neural oscillations are theorized to be necessary for interregional communication. Synchrony between the frontal and parietal cortex increases during cognitive control. Polanía et al. used a novel three electrode montage to synchronize the frontal and parietal cortex in-phase or anti-phase. Participants receive the stimulation during performance of a working memory task. In-phase stimulation increased behavioral performance and anti-phase stimulation decreased performance. Pros:
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Contributed by: Justin Riddle, PhD Slow theta tACS of the right parietal cortex enhances contralateral visual working memory capacity10/15/2021 Bender, Monika, Vincenzo Romei, and Paul Sauseng. 2019. 'Slow theta tACS of the right parietal cortex enhances contralateral visual working memory capacity', Brain topography, 32: 477-81.
Summary: The brain is wired such that the right side of the brain processes the left side of space. Bender et al. delivered slow theta frequency tACS focally to the right hemisphere during a working memory task. Visual items to be encoded into memory are presented in the left or right visual field. Participants that received slow theta to the right parietal cortex showed increased working memory capacity only for memory items on the left visual field. Pros:
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Contributed by: Justin Riddle, PhD Reinhart, Robert MG, and John A Nguyen. 2019. 'Working memory revived in older adults by synchronizing rhythmic brain circuits', Nature neuroscience, 22: 820-27.
Summary: Theta oscillations couple to gamma oscillations to support working memory. However, in healthy aging these oscillations become uncoupled resulting in reduced working memory capacity. Reinhart and Nguyen delivered high-definition tACS to both prefrontal and auditory cortex in synchrony and found that theta-gamma coupling was restored in older participants. The older participants showed performance level similar to the younger participants. Stimulation was only effective when synchronizing frontal and auditory, but was not effective to either region individually. Pros:
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Contributed by: Justin Riddle, PhD Wolinski, Nina, Nicholas R Cooper, Paul Sauseng, and Vincenzo Romei. 2018. 'The speed of parietal theta frequency drives visuospatial working memory capacity', PLoS biology, 16: e2005348.
Summary: Humans have limited capacity to hold information in mind, or working memory. Previous research shows that slower theta oscillations (4-8Hz) correlates with greater working memory capacity. Wolinski et al. delivered tACS at a slower theta frequency and a faster theta frequency. Slower theta frequency tACS improves working memory capacity relative to faster theta frequency tACS. Pros:
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Contributed by: Justin Riddle, PhD Chai, Yuhui, Jingwei Sheng, Peter A Bandettini, and Jia‐Hong Gao. 2018. 'Frequency‐dependent t ACS modulation of BOLD signal during rhythmic visual stimulation', Human brain mapping, 39: 2111-20.
Summary: Transcranial alternating current stimulation (tACS) is able to modulate neural activity. However, the spread of tACS effects in the brain is unknown. Using concurrent tACS and fMRI Chai et al. delivered 8 Hz stimulation to visual cortex during presentation of a flickering checkerboard gradient at 8 Hz. They found that stimulus-modulated visual cortical activation was increased by stimulation matched to the rate of the flickering checkerboard. These effects were strongest with 8 Hz tACS, weaker at its harmonic 4 Hz, and no present with 16 Hz tACS. TACS may be most effective at boosting ongoing neural activity when aligned to that activity or at its harmonic frequency. Pros:
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Contributed by: Justin Riddle, PhD Wischnewski, Miles, Paul Zerr, and Dennis JLG Schutter. 2016. 'Effects of theta transcranial alternating current stimulation over the frontal cortex on reversal learning', Brain stimulation, 9: 705-11.
Summary: Theta oscillations are generated after notification of a reward or loss in reinforcement learning paradigms. Wischnewski et al., delivered theta-frequency transcranial alternating current stimulation (tACS) bifrontally during performance of a reward-based reinforcement learning task. Participants that receive theta-tACS were quicker to learn that a decision was less rewarding and quicker to re-learn its value when it was re-instated as rewarding. EEG results revealed that theta-tACS decreased theta oscillations (and theta-beta ratio) as measured by rest after versus before the task. These results provide causal evidence for theta oscillations in reward learning. Pros:
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Contributed by: Justin Riddle, PhD Alekseichuk, Ivan, Stefanie Corinna Pabel, Andrea Antal, and Walter Paulus. 2017. 'Intrahemispheric theta rhythm desynchronization impairs working memory', Restorative neurology and neuroscience, 35: 147-58.
Summary: Synchronization between the left and right hemisphere has been shown to correlate with improved performance in a variety of cognitive and motor tasks. Alekseichuk et al. delivered transcranial alternating current stimulation (tACS) in theta frequency (6Hz) to four locations on the scalp, left and right frontal and parietal cortex, to either synchronize within hemisphere or across hemispheres during performance of a working memory task. Only stimulation that desynchronized the hemispheres disrupted performance – increased reaction time and decreased accuracy – relative to placebo and no stimulation. EEG taken after the task found a decrease in function connectivity across the scalp from desynchronizing tACS. These findings provide causal evidence for the role of interhemispheric connectivity in working memory processing. Pros:
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Contributed by: Justin Riddle, PhD Modulation of large-scale cortical coupling by transcranial alternating current stimulation10/15/2021 Schwab, Bettina C, Jonas Misselhorn, and Andreas K Engel. 2019. 'Modulation of large-scale cortical coupling by transcranial alternating current stimulation', Brain stimulation, 12: 1187-96.
Summary: Neural oscillations synchronized between regions is proposed to be a mechanism for information transfer between areas. Schwab et al., delivered alpha-frequency transcranial alternating current stimulation (tACS) either in-phase, anti-phase, or with a randomized and changing phase difference using high-density tACS to bi-occipital cortex. In-phase tACS selectively increased alpha frequency connectivity between the stimulated occipital cortices relative to anti-phase and random-phase was intermediary. Both in-phase and anti-phase equally increased alpha power. Source localization revealed spatial specificity of the connectivity changes to the stimulated regions. The study demonstrates the spatial and temporal power of tACS to modulate the functional connection between brain regions. Pros:
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Contributed by: Justin Riddle, PhD |
AuthorsEvery week, there are new and exciting scientific papers published on studies that investigated tACS. Reading and understanding these papers unfortunately requires both access to (sometimes quite expensive) scientific journals and in-depth "insider knowledge." Our goal is to share with you brief summaries of tACS studies that give you a big-picture idea of what the publications are about. There are too many studies to feature all of them but we will continuously update this page. If you have a specific study you would like to get featured, please contact us. The contributors are personnel from the Frohlich Lab and the Carolina Center for Neurostimulation. ArchivesCategories |
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