scholarly journals Perception of Rhythmic Speech Is Modulated by Focal Bilateral Transcranial Alternating Current Stimulation

2020 ◽  
Vol 32 (2) ◽  
pp. 226-240 ◽  
Author(s):  
Benedikt Zoefel ◽  
Isobella Allard ◽  
Megha Anil ◽  
Matthew H. Davis
Keyword(s):  
Speech Perception ◽  
Speech Processing ◽  
Alternating Current ◽  
Stream Segregation ◽  
Causal Role ◽  
Oscillatory Activity ◽  
Transcranial Alternating Current Stimulation ◽  
Neural Entrainment ◽  
Actual Speech

Several recent studies have used transcranial alternating current stimulation (tACS) to demonstrate a causal role of neural oscillatory activity in speech processing. In particular, it has been shown that the ability to understand speech in a multi-speaker scenario or background noise depends on the timing of speech presentation relative to simultaneously applied tACS. However, it is possible that tACS did not change actual speech perception but rather auditory stream segregation. In this study, we tested whether the phase relation between tACS and the rhythm of degraded words, presented in silence, modulates word report accuracy. We found strong evidence for a tACS-induced modulation of speech perception, but only if the stimulation was applied bilaterally using ring electrodes (not for unilateral left hemisphere stimulation with square electrodes). These results were only obtained when data were analyzed using a statistical approach that was identified as optimal in a previous simulation study. The effect was driven by a phasic disruption of word report scores. Our results suggest a causal role of neural entrainment for speech perception and emphasize the importance of optimizing stimulation protocols and statistical approaches for brain stimulation research.

scholarly journals Perception of rhythmic speech is modulated by focal bilateral tACS

2019 ◽  
Author(s):  
Benedikt Zoefel ◽  
Isobella Allard ◽  
Megha Anil ◽  
Matthew H Davis
Keyword(s):  
Speech Perception ◽  
Speech Processing ◽  
Stream Segregation ◽  
Causal Role ◽  
Oscillatory Activity ◽  
Auditory Stream Segregation ◽  
Neural Entrainment ◽  
Actual Speech ◽  
Speech Presentation

AbstractSeveral recent studies have used transcranial alternating stimulation (tACS) to demonstrate a causal role of neural oscillatory activity in speech processing. In particular, it has been shown that the ability to understand speech in a multi-speaker scenario or background noise depends on the timing of speech presentation relative to simultaneously applied tACS. However, it is possible that tACS did not change actual speech perception but rather auditory stream segregation. In this study, we tested whether the phase relation between tACS and the rhythm of degraded words, presented in silence, modulates word report accuracy. We found strong evidence for a tACS-induced modulation of speech perception, but only if the stimulation was applied bilaterally using ring electrodes (not for unilateral left hemisphere stimulation with square electrodes). These results were only obtained when data was analyzed using a statistical approach that was identified as optimal in a previous simulation study. The effect was driven by a phasic disruption of word report scores. Our results suggest a causal role of neural entrainment for speech perception and emphasize the importance of optimizing stimulation protocols and statistical approaches for brain stimulation research.

scholarly journals Biasing the Perception of Spoken Words with Transcranial Alternating Current Stimulation

2020 ◽  
Vol 32 (8) ◽  
pp. 1428-1437
Author(s):  
Anne Kösem ◽  
Hans Rutger Bosker ◽  
Ole Jensen ◽  
Peter Hagoort ◽  
Lars Riecke
Keyword(s):  
Speech Processing ◽  
Alternating Current ◽  
Spoken Word ◽  
Word Perception ◽  
Transcranial Alternating Current Stimulation ◽  
Neural Entrainment ◽  
The Difference ◽  
Auditory Cortices ◽  
Speech Segments ◽  
The Impact

Recent neuroimaging evidence suggests that the frequency of entrained oscillations in auditory cortices influences the perceived duration of speech segments, impacting word perception [Kösem, A., Bosker, H. R., Takashima, A., Meyer, A., Jensen, O., & Hagoort, P. Neural entrainment determines the words we hear. Current Biology, 28, 2867–2875, 2018]. We further tested the causal influence of neural entrainment frequency during speech processing, by manipulating entrainment with continuous transcranial alternating current stimulation (tACS) at distinct oscillatory frequencies (3 and 5.5 Hz) above the auditory cortices. Dutch participants listened to speech and were asked to report their percept of a target Dutch word, which contained a vowel with an ambiguous duration. Target words were presented either in isolation (first experiment) or at the end of spoken sentences (second experiment). We predicted that the tACS frequency would influence neural entrainment and therewith how speech is perceptually sampled, leading to a perceptual overestimation or underestimation of the vowel's duration. Whereas results from Experiment 1 did not confirm this prediction, results from Experiment 2 suggested a small effect of tACS frequency on target word perception: Faster tACS leads to more long-vowel word percepts, in line with the previous neuroimaging findings. Importantly, the difference in word perception induced by the different tACS frequencies was significantly larger in Experiment 1 versus Experiment 2, suggesting that the impact of tACS is dependent on the sensory context. tACS may have a stronger effect on spoken word perception when the words are presented in continuous speech as compared to when they are isolated, potentially because prior (stimulus-induced) entrainment of brain oscillations might be a prerequisite for tACS to be effective.

scholarly journals Probing the causal role of prestimulus interregional synchrony for perceptual integration via tACS

2016 ◽  
Author(s):  
Rolandas Stonkus ◽  
Verena Braun ◽  
Jess Kerlin ◽  
Gregor Volberg ◽  
Simon Hanslmayr
Keyword(s):  
Specific Activity ◽  
Brain Regions ◽  
Causal Role ◽  
Oscillatory Activity ◽  
Perceptual Integration ◽  
After Effects ◽  
Activity Phase ◽  
Fmri Study ◽  
Transcranial Alternating Current Stimulation

The phase of prestimulus oscillations at 7-10 Hz has been shown to modulate perception of briefly presented visual stimuli. Specifically, a recent combined EEG-fMRI study suggested that a prestimulus oscillation at around 7 Hz represents open and closed windows for perceptual integration by modulating connectivity between lower order occipital and higher order parietal brain regions. We here utilized brief event-related transcranial alternating current stimulation (tACS) to specifically modulate this prestimulus 7 Hz oscillation, and the synchrony between parietal and occipital brain regions. To this end we tested for a causal role of this particular prestimulus oscillation for perceptual integration. The EEG was acquired at the same time allowing us to investigate frequency specific after effects phase-locked to stimulation offset. On a behavioural level our results suggest that the tACS did modulate perceptual integration, however, in an unexpected manner. On an electrophysiological level our results suggest that brief tACS does induce oscillatory entrainment, as visible in frequency specific activity phase-locked to stimulation offset. Together, our results do not strongly support a causal role of prestimulus 7 Hz oscillations for perceptual integration. However, our results suggest that brief tACS is capable of modulating oscillatory activity in a temporally sensitive manner.

scholarly journals Sustained neural rhythms reveal endogenous oscillations supporting speech perception

PLoS Biology ◽  
2021 ◽  
Vol 19 (2) ◽  
pp. e3001142
Author(s):  
Sander van Bree ◽  
Ediz Sohoglu ◽  
Matthew H. Davis ◽  
Benedikt Zoefel
Keyword(s):  
Electrical Stimulation ◽  
Speech Perception ◽  
Oscillatory Activity ◽  
Neural Oscillations ◽  
Evoked Responses ◽  
Sustained Effects ◽  
Brain Responses ◽  
Underlying Principle ◽  
Transcranial Alternating Current Stimulation ◽  
Neural Entrainment

Rhythmic sensory or electrical stimulation will produce rhythmic brain responses. These rhythmic responses are often interpreted as endogenous neural oscillations aligned (or “entrained”) to the stimulus rhythm. However, stimulus-aligned brain responses can also be explained as a sequence of evoked responses, which only appear regular due to the rhythmicity of the stimulus, without necessarily involving underlying neural oscillations. To distinguish evoked responses from true oscillatory activity, we tested whether rhythmic stimulation produces oscillatory responses which continue after the end of the stimulus. Such sustained effects provide evidence for true involvement of neural oscillations. In Experiment 1, we found that rhythmic intelligible, but not unintelligible speech produces oscillatory responses in magnetoencephalography (MEG) which outlast the stimulus at parietal sensors. In Experiment 2, we found that transcranial alternating current stimulation (tACS) leads to rhythmic fluctuations in speech perception outcomes after the end of electrical stimulation. We further report that the phase relation between electroencephalography (EEG) responses and rhythmic intelligible speech can predict the tACS phase that leads to most accurate speech perception. Together, we provide fundamental results for several lines of research—including neural entrainment and tACS—and reveal endogenous neural oscillations as a key underlying principle for speech perception.

scholarly journals The causal role of transcranial alternating current stimulation at alpha frequency in boosting visual perceptual learning

2021 ◽  
Author(s):  
Qing He ◽  
Baoqi Gong ◽  
Keyan Bi ◽  
Fang Fang
Keyword(s):  
Perceptual Learning ◽  
Discrimination Learning ◽  
Alternating Current ◽  
Causal Role ◽  
Orientation Discrimination ◽  
Visual Perceptual Learning ◽  
Specific Manner ◽  
Transcranial Alternating Current Stimulation ◽  
40 Hz

Extensive training improves our ability to perceive visual contents around us, a phenomenon known as visual perceptual learning (VPL). Numerous studies have been conducted to understand the mechanisms of VPL, while the neural oscillatory mechanisms underpinning VPL has yet to be elucidated. To this end, we adopted transcranial alternating current stimulation (tACS), a neuromodulatory technique that can alter ongoing brain rhythms in a frequency-specific manner by applying external weak electric fields, to stimulate targeted cortical areas in human subjects while they performed an orientation discrimination learning task. Five groups of subjects undertook five daily training sessions to execute the task. Four groups received occipital tACS stimulation at 10 Hz (alpha band), 20 Hz (beta band), 40 Hz (gamma band), or sham 10 Hz (sham), and one group was stimulated at the sensorimotor regions by 10 Hz tACS. Compared with the sham stimulation, occipital tACS at 10 Hz, but not at 20 Hz or 40 Hz, increased both the learning rate and performance improvement. However, when 10 Hz tACS was delivered to the sensorimotor areas, the modulatory effects of tACS were absent, suggesting that tACS modulated the orientation discrimination learning in a frequency- and location-specific manner. Moreover, the tACS-induced enhancement lasted at least two months after the termination of training. Our findings provide strong evidence for the causal role of alpha oscillations in VPL and shed new light on the design of effective neuromodulation protocols that might facilitate rehabilitation for patients with neuro-ophthalmological disorders.

scholarly journals Transcranial alternating current stimulation (tACS) reveals causal role of brain oscillations in visual attention

2016 ◽  
Vol 16 (12) ◽  
pp. 937 ◽  
Author(s):  
Daniel Baldauf ◽  
Nir Grossman ◽  
An-Ming Hu ◽  
Ed Boyden ◽  
Robert Desimone
Keyword(s):  
Visual Attention ◽  
Alternating Current ◽  
Causal Role ◽  
Brain Oscillations ◽  
Transcranial Alternating Current Stimulation

scholarly journals The role of alpha oscillations in a premotor-cerebellar loop in modulation of motor learning: insights from transcranial alternating current stimulation

2020 ◽  
Author(s):  
Christine Schubert ◽  
Alhuda Dabbagh ◽  
Joseph Classen ◽  
Ulrike M. Krämer ◽  
Elinor Tzvi
Keyword(s):  
Motor Learning ◽  
Sequence Learning ◽  
Premotor Cortex ◽  
Alternating Current ◽  
Oscillatory Activity ◽  
Motor Sequence Learning ◽  
Motor Sequence ◽  
Alpha Oscillations ◽  
Transcranial Alternating Current Stimulation

AbstractAlpha oscillations (8-13 Hz) have been shown to play an important role in dynamic neural processes underlying learning and memory. The goal of this study was to scrutinize the role of α oscillations in communication within a network implicated in motor sequence learning. To this end, we conducted two experiments using the serial reaction time task. In the first experiment, we explored changes in α power and cross-channel α coherence. We found a gradual decrease in learning-related α power over left premotor cortex (PMC), somatosensory cortex (S1) and tempo-parietal junction (TPJ). Alpha coherence between left PMC/S1 and right cerebellar crus I was reduced for sequence learning, possibly reflecting a functional decoupling in a motor-cerebellar loop during the motor learning process. In the second experiment in a different cohort, we applied 10Hz transcranial alternating current stimulation (tACS), a method shown to entrain local oscillatory activity, to left M1 (lM1) and right cerebellum (rCB) during sequence learning. We observed learning deficits during rCB tACS compared to sham, but not during lM1 tACS. In addition, learning-related α power following rCB tACS was increased in left PMC, possibly reflecting a decrease in neural activity. Importantly, learning-specific coherence between left PMC and right cerebellar lobule VIIb was enhanced following rCB tACS. These findings suggest that interactions within a premotor-cerebellar loop, which are underlying motor sequence learning, are mediated by α oscillations. We show that they can be modulated through external entrainment of cerebellar oscillations, which then modulates motor cortical α and interferes with sequence learning.

scholarly journals Binding Mechanisms in Visual Perception and Their Link With Neural Oscillations: A Review of Evidence From tACS

2021 ◽  
Vol 12 ◽  
Author(s):  
Andrea Ghiani ◽  
Marcello Maniglia ◽  
Luca Battaglini ◽  
David Melcher ◽  
Luca Ronconi
Keyword(s):  
Visual Perception ◽  
Feature Binding ◽  
Causal Role ◽  
Oscillatory Activity ◽  
Dependent Manner ◽  
Brain Oscillations ◽  
Temporal Binding ◽  
Neurophysiological Studies ◽  
Binding Mechanisms

Neurophysiological studies in humans employing magneto- (MEG) and electro- (EEG) encephalography increasingly suggest that oscillatory rhythmic activity of the brain may be a core mechanism for binding sensory information across space, time, and object features to generate a unified perceptual representation. To distinguish whether oscillatory activity is causally related to binding processes or whether, on the contrary, it is a mere epiphenomenon, one possibility is to employ neuromodulatory techniques such as transcranial alternating current stimulation (tACS). tACS has seen a rising interest due to its ability to modulate brain oscillations in a frequency-dependent manner. In the present review, we critically summarize current tACS evidence for a causal role of oscillatory activity in spatial, temporal, and feature binding in the context of visual perception. For temporal binding, the emerging picture supports a causal link with the power and the frequency of occipital alpha rhythms (8–12 Hz); however, there is no consistent evidence on the causal role of the phase of occipital tACS. For feature binding, the only study available showed a modulation by occipital alpha tACS. The majority of studies that successfully modulated oscillatory activity and behavioral performance in spatial binding targeted parietal areas, with the main rhythms causally linked being the theta (~7 Hz) and beta (~18 Hz) frequency bands. On the other hand, spatio-temporal binding has been directly modulated by parieto-occipital gamma (~40–60 Hz) and alpha (10 Hz) tACS, suggesting a potential role of cross-frequency coupling when binding across space and time. Nonetheless, negative or partial results have also been observed, suggesting methodological limitations that should be addressed in future research. Overall, the emerging picture seems to support a causal role of brain oscillations in binding processes and, consequently, a certain degree of plasticity for shaping binding mechanisms in visual perception, which, if proved to have long lasting effects, can find applications in different clinical populations.

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