scholarly journals Amplitude modulated transcranial alternating current stimulation (AM-TACS) efficacy evaluation via phosphene induction

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Carsten Thiele ◽  
Tino Zaehle ◽  
Aiden Haghikia ◽  
Philipp Ruhnau
Keyword(s):  
Amplitude Modulation ◽  
Carrier Frequency ◽  
Alternating Current ◽  
Efficacy Evaluation ◽  
Electrophysiological Signals ◽  
Transcranial Alternating Current Stimulation ◽  
Novel Method ◽  
The Right

AbstractAmplitude modulated transcranial alternating current stimulation (AM-tACS) is a novel method of electrostimulation which enables the recording of electrophysiological signals during stimulation, thanks to an easier removable stimulation artefact compared to classical electrostimulation methods. To gauge the neuromodulatory potential of AM-tACS, we tested its capacity to induce phosphenes as an indicator of stimulation efficacy. AM-tACS was applied via a two-electrode setup, attached on FpZ and below the right eye. AM-tACS waveforms comprised of different carrier (50 Hz, 200 Hz, 1000 Hz) and modulation frequencies (8 Hz, 16 Hz, 28 Hz) were administered with at maximum 2 mA peak-to-peak stimulation strength. TACS conditions in the same frequencies were used as a benchmark for phosphene induction. AM-tACS conditions using a 50 Hz carrier frequency were able to induce phosphenes, but with no difference in phosphene thresholds between modulation frequencies. AM-tACS using a 200 Hz or 1000 Hz carrier frequency did not induce phosphenes. TACS conditions induced phosphenes in line with previous studies. Stimulation effects of AM-tACS conditions were independent of amplitude modulation and instead relied solely on the carrier frequency. A possible explanation may be that AM-tACS needs higher stimulation intensities for its amplitude modulation to have a neuromodulatory effect.

scholarly journals Transient amplitude modulation of alpha-band oscillations by short-time intermittent closed-loop tACS

2020 ◽  
Author(s):  
G. Zarubin ◽  
C. Gundlach ◽  
V. Nikulin ◽  
A. Villringer ◽  
M. Bogdan
Keyword(s):  
Individual Differences ◽  
Visual System ◽  
Amplitude Modulation ◽  
Closed Loop ◽  
Alternating Current ◽  
Stimulation Protocol ◽  
Spatial Filters ◽  
Alpha Oscillations ◽  
Transcranial Alternating Current Stimulation ◽  
Short Time

AbstractNon-invasive brain stimulation techniques such as transcranial alternating current stimulation (tACS) have recently become extensively utilized due to their potential to modulate ongoing neuronal oscillatory activity and consequently to induce cortical plasticity relevant for various cognitive functions. However, the neurophysiological basis for stimulation effects as well as their inter-individual differences are not yet understood. In the present study we used a closed-loop EEG transcranial alternating current stimulation protocol (EEG-tACS) to examine the modulation of alpha oscillations generated in occipito-parietal areas. In particular, we investigated the effects of a repeated short-time intermittent stimulation protocol (1 s in every trial) applied over the visual cortex (Cz and Oz) and adjusted according to the phase and frequency of visual alpha oscillations on the amplitude of these oscillations. Based on previous findings, we expected higher increases in alpha amplitudes for tACS applied in-phase with ongoing oscillations as compared to an application in anti-phase and this modulation to be present in low-alpha amplitude states of the visual system (eyes opened) but not high (eyes closed).Contrary to our expectations, we found a transient suppression of alpha power in inter-individually derived spatially specific parieto-occipital components obtained via the estimation of spatial filters by using the common spatial patterns approach. The amplitude modulation was independent of the phase relationship between tACS signal and alpha oscillations, and the state of the visual system manipulated via closed- and open-eye conditions. It was also absent in conventionally analyzed single-channel and multi-channel data from an average parieto-occipital region.The fact that the tACS modulation of oscillations was phase-independent suggests that mechanisms driving the effects of tACS may not be explained by entrainment alone, but rather require neuroplastic changes or transient disruption of neural oscillations. Our study also supports the notion that the response to tACS is subject specific, where the modulatory effects are shaped by the interplay between the stimulation and different alpha generators. This favors stimulation protocols as well as analysis regimes exploiting inter-individual differences, such as spatial filters to reveal otherwise hidden stimulation effects and, thereby, comprehensively induce and study the effects and underlying mechanisms of tACS.

scholarly journals Closed-loop transcranial alternating current stimulation of slow oscillations

2015 ◽  
Vol 1 (1) ◽  
pp. 85-88 ◽  
Author(s):  
Christian Wilde ◽  
Ralf Bruder ◽  
Sonja Binder ◽  
Lisa Marshall ◽  
Achim Schweikard
Keyword(s):  
Closed Loop ◽  
Alternating Current ◽  
Electrical Measurements ◽  
Slow Oscillations ◽  
Non Invasive ◽  
Transcranial Alternating Current Stimulation ◽  
Novel Method ◽  
Endogenous Activity ◽  
Stimulation Of

AbstractTranscranial alternating current stimulation (tACS) is an emerging non-invasive tool for modulating brain oscillations. There is evidence that weak oscillatory electrical stimulation during sleep can entrain cortical slow oscillations to improve the memory consolidation in rodents and humans. Using a novel method and a custom built stimulation device, automatic stimulation of slow oscillations in-phase with the endogenous activity in a real-time closed-loop setup is possible. Preliminary data from neuroplasticity experiments show a high detection performance of the proposed method, electrical measurements demonstrate the outstanding quality of the presented stimulation device.

scholarly journals Alpha and Theta Transcranial Alternating Current Stimulation Over the Right Dorsolateral Prefrontal Cortex Modulates Vigilance Performance, but Only When Arousal Levels Are Non-optimal

2021 ◽  
Author(s):  
Víctor Martínez-Pérez ◽  
Miriam Tortajada ◽  
Lucía B. Palmero ◽  
Guillermo Campoy ◽  
Luis J. Fuentes
Keyword(s):  
Prefrontal Cortex ◽  
Dorsolateral Prefrontal Cortex ◽  
Alternating Current ◽  
Time Of Day ◽  
Time On Task ◽  
Frontoparietal Network ◽  
Dorsolateral Prefrontal ◽  
Transcranial Alternating Current Stimulation ◽  
The Right

Abstract BackgroundCurrent theoretical accounts on the oscillatory nature of sustained attention predict that entrainment via transcranial alternating current stimulation (tACS) at alpha and theta frequencies on the frontoparietal network could prevent the drops in vigilance across time-on-task. Nonetheless, most previous studies have neglected both the fact that vigilance comprises two dissociable components (i.e. arousal and executive vigilance) and the potential role of differences in arousal baseline. MethodWe examined the effects of theta- and alpha-tACS over the right dorsolateral prefrontal cortex on both components of vigilance and on participants that differed in arousal baseline according to their chronotype and the time of testing. Intermediate-types performed the vigilance tasks when their arousal baseline was at the optimal level, whereas evening-types performed the vigilance tasks when their arousal baseline was at non-optimal levels. ResultsBoth theta- and alpha-tACS improved arousal vigilance, whereas alpha-tACS, but not theta-tACS, improved accuracy and attenuated the typical vigilance decrement in the executive vigilance task. Importantly, these stimulation effects were only found when arousal baseline was low (i.e., with evening-types performing the tasks at their non-optimal time of day).ConclusionThe results support the multicomponent view of vigilance, the relevance of heeding individual differences in arousal baseline, and the role of alpha oscillations as a long-range cortical scale synchronization mechanism that compensates the decrements in performance as a function of time-on-task by exerting and maintaining cognitive control attributed to activation of the frontoparietal network.

scholarly journals Frequency but not phase specific modulation of binocular rivalry with transcranial alternating current stimulation

2019 ◽  
Author(s):  
Jorge Delgado ◽  
Guillaume Riesen ◽  
Vladimir Y. Vildavski ◽  
Anthony M. Norcia
Keyword(s):  
Visual Stimulus ◽  
Binocular Rivalry ◽  
Control Experiment ◽  
Visual Stimuli ◽  
Alternating Current ◽  
Specific Model ◽  
Transcranial Alternating Current Stimulation ◽  
The Right

ABSTRACTRecent transcranial alternating current stimulation (tACS) literature suggests that tACS effects can in principle be both frequency and phase specific. In a series of three experiments using 69 participants used binocular rivalry percepts as a read-out for the effects of phase-synchronized tACS stimulation. To test for phase specificity, with frequency the same in each eye, we visually stimulated each eye with 3Hz, with stimuli in each eye presented in temporal in antiphase. The frequency-specific paradigm visually stimulated the right eye with 3Hz, and the left eye with 5Hz. Each experiment was accompanied by 3Hz tACS, whose phase with respect to the visual stimulus was varied by 0°, 90°, 180°, or 270° in relation to the right eye’s stimulus. A baseline no-tACS block preceded the stimulation blocks and two more followed, immediately and ten minutes after. Individual blocks lasted 4 minutes. Additionally, a no-tACS control experiment identical to the 3 Hz anti-phase visual stimuli setup was conducted, keeping all parameters the same but eliminating tACS. During stimulation, the 3 Hz anti-phase visual stimuli setup slowed the rate of rivalry in both eyes. Conversely, the 3Hz-right, 5Hz-left setup slowed the right (targeted) eye significantly while leaving the left (unstimulated) eye unchanged. In both experiments, durations returned to baseline after 10 minutes. Our results are consistent with the frequency-specific model of tACS, and with the Leveltian hypothesis that stimulation weakens the stimulated eye, as the right eye got weaker when it was directly targeted, and both eyes got weaker when targeted in antiphase. tACS does not appear to preferentially modulating percept durations in one phase more than in another.

scholarly journals Effects of transcranial alternating current stimulation over right-DLPFC on vigilance tasks depend on the arousal level

2022 ◽  
Vol 12 (1) ◽  
Author(s):  
Víctor Martínez-Pérez ◽  
Miriam Tortajada ◽  
Lucía B. Palmero ◽  
Guillermo Campoy ◽  
Luis J. Fuentes
Keyword(s):  
Prefrontal Cortex ◽  
Sustained Attention ◽  
Dorsolateral Prefrontal Cortex ◽  
Alternating Current ◽  
Arousal Level ◽  
Time On Task ◽  
Dorsolateral Prefrontal ◽  
Transcranial Alternating Current Stimulation ◽  
The Right

AbstractCurrent theoretical accounts on the oscillatory nature of sustained attention predict that entrainment via transcranial alternating current stimulation (tACS) at alpha and theta frequencies on specific areas of the prefrontal cortex could prevent the drops in vigilance across time-on-task. Nonetheless, most previous studies have neglected both the fact that vigilance comprises two dissociable components (i.e., arousal and executive vigilance) and the potential role of differences in arousal levels. We examined the effects of theta- and alpha-tACS over the right dorsolateral prefrontal cortex in both components of vigilance and in participants who differed in arousal level according to their chronotype and time of testing. Intermediate-types performed the vigilance tasks when their arousal level was optimal, whereas evening-types performed the vigilance tasks when their arousal levels were non-optimal. Both theta- and alpha-tACS improved arousal vigilance in the psychomotor vigilance task (PVT), whereas alpha-tACS, but not theta-tACS, improved executive vigilance in the sustained attention to response task (SART), and counteracted the typical vigilance decrement usually observed in this task. Importantly, these stimulation effects were only found when arousal was low (i.e., with evening-types performing the tasks at their non-optimal time of day). The results support the multicomponent view of vigilance, the relevance of heeding individual differences in arousal, and the role of alpha oscillations as a long-range cortical scale synchronization mechanism that compensates the decrements in performance as a function of time-on-task by exerting and maintaining cognitive control attributed to activation of the right dorsolateral prefrontal cortex.

Sign in / Sign up

Export Citation Format

Share Document