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Harquel S, Cian C, Torlay L, Cousin E, Barraud PA, Bougerol T, Guerraz M. Modulation of Visually Induced Self-motion Illusions by α Transcranial Electric Stimulation over the Superior Parietal Cortex. J Cogn Neurosci 2024; 36:143-154. [PMID: 37870524 DOI: 10.1162/jocn_a_02074] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2023]
Abstract
The growing popularity of virtual reality systems has led to a renewed interest in understanding the neurophysiological correlates of the illusion of self-motion (vection), a phenomenon that can be both intentionally induced or avoided in such systems, depending on the application. Recent research has highlighted the modulation of α power oscillations over the superior parietal cortex during vection, suggesting the occurrence of inhibitory mechanisms in the sensorimotor and vestibular functional networks to resolve the inherent visuo-vestibular conflict. The present study aims to further explore this relationship and investigate whether neuromodulating these waves could causally affect the quality of vection. In a crossover design, 22 healthy volunteers received high amplitude and focused α-tACS (transcranial alternating current stimulation) over the superior parietal cortex while experiencing visually induced vection triggered by optokinetic stimulation. The tACS was tuned to each participant's individual α peak frequency, with θ-tACS and sham stimulation serving as controls. Overall, participants experienced better quality vection during α-tACS compared with control θ-tACS and sham stimulations, as quantified by the intensity of vection. The observed neuromodulation supports a causal relationship between parietal α oscillations and visually induced self-motion illusions, with their entrainment triggering overinhibition of the conflict within the sensorimotor and vestibular functional networks. These results confirm the potential of noninvasive brain stimulation for modulating visuo-vestibular conflicts, which could help to enhance the sense of presence in virtual reality environments.
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Affiliation(s)
- Sylvain Harquel
- Université Grenoble-Alpes, Université Savoie Mont Blanc, CNRS, UMR5105, LPNC, Grenoble, France
- Defitech Chair of Clinical Neuroengineering, Center for Neuroprosthetics (CNP) and Brain Mind Institute (BMI), Swiss Federal Institute of Technology Lausanne (EPFL), Campus Biotech, Geneva, Switzerland
| | - Corinne Cian
- Université Grenoble-Alpes, Université Savoie Mont Blanc, CNRS, UMR5105, LPNC, Grenoble, France
- Institut de Recherche Biomédicale des Armées, Brétigny sur Orge, France
| | - Laurent Torlay
- Université Grenoble-Alpes, Université Savoie Mont Blanc, CNRS, UMR5105, LPNC, Grenoble, France
| | - Emilie Cousin
- Université Grenoble-Alpes, Université Savoie Mont Blanc, CNRS, UMR5105, LPNC, Grenoble, France
| | - Pierre-Alain Barraud
- Université Grenoble-Alpes, CNRS, CHU Grenoble-Alpes, Grenoble INP, TIMC-IMAG, Grenoble, France
| | - Thierry Bougerol
- Centre Hospitalier Université Grenoble-Alpes, Pôle Psychiatrie, Grenoble, France
- Université Grenoble-Alpes, Inserm, U1216, Grenoble Institut des Neurosciences, Grenoble, France
| | - Michel Guerraz
- Université Grenoble-Alpes, Université Savoie Mont Blanc, CNRS, UMR5105, LPNC, Grenoble, France
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De Koninck BP, Brazeau D, Guay S, Herrero Babiloni A, De Beaumont L. Transcranial Alternating Current Stimulation to Modulate Alpha Activity: A Systematic Review. Neuromodulation 2023; 26:1549-1584. [PMID: 36725385 DOI: 10.1016/j.neurom.2022.12.007] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2022] [Revised: 12/05/2022] [Accepted: 12/08/2022] [Indexed: 02/01/2023]
Abstract
BACKGROUND Transcranial alternating current stimulation (tACS) has been one of numerous investigation methods used for their potential to modulate brain oscillations; however, such investigations have given contradictory results and a lack of standardization. OBJECTIVES In this systematic review, we aimed to assess the potential of tACS to modulate alpha spectral power. The secondary outcome was the identification of tACS methodologic key parameters, adverse effects, and sensations. MATERIALS AND METHODS Studies in healthy adults who were receiving active and sham tACS intervention or any differential condition were included. The main outcome assessed was the increase/decrease of alpha spectral power through either electroencephalography or magnetoencephalography. Secondary outcomes were methodologic parameters, sensation reporting, and adverse effects. Risks of bias and the study quality were assessed with the Cochrane assessment tool. RESULTS We obtained 1429 references, and 20 met the selection criteria. A statistically significant alpha-power increase was observed in nine studies using continuous tACS stimulation and two using intermittent tACS stimulation set at a frequency within the alpha range. A statistically significant alpha-power increase was observed in three more studies using a stimulation frequency outside the alpha range. Heterogeneity among stimulation parameters was recognized. Reported adverse effects were mild. The implementation of double blind was identified as challenging using tACS, in part owing to electrical artifacts generated by stimulation on the recorded signal. CONCLUSIONS Most assessed studies reported that tACS has the potential to modulate brain alpha power. The optimization of this noninvasive brain stimulation method is of interest mostly for its potential clinical applications with neurological conditions associated with perturbations in alpha brain activity. However, more research efforts are needed to standardize optimal parameters to achieve lasting modulation effects, develop methodologic alternatives to reduce experimental bias, and improve the quality of studies using tACS to modulate brain activity.
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Affiliation(s)
- Beatrice P De Koninck
- Sports and Trauma Applied Research Lab, Montreal Sacred Heart Hospital, CIUSSS North-Montreal-Island, Montreal, Quebec, Canada; University of Montreal, Montréal, Quebec, Canada.
| | - Daphnée Brazeau
- Sports and Trauma Applied Research Lab, Montreal Sacred Heart Hospital, CIUSSS North-Montreal-Island, Montreal, Quebec, Canada; University of Montreal, Montréal, Quebec, Canada
| | - Samuel Guay
- Sports and Trauma Applied Research Lab, Montreal Sacred Heart Hospital, CIUSSS North-Montreal-Island, Montreal, Quebec, Canada; University of Montreal, Montréal, Quebec, Canada
| | - Alberto Herrero Babiloni
- Sports and Trauma Applied Research Lab, Montreal Sacred Heart Hospital, CIUSSS North-Montreal-Island, Montreal, Quebec, Canada; University of Montreal, Montréal, Quebec, Canada; McGill University, Montreal, Quebec, Canada
| | - Louis De Beaumont
- Sports and Trauma Applied Research Lab, Montreal Sacred Heart Hospital, CIUSSS North-Montreal-Island, Montreal, Quebec, Canada; University of Montreal, Montréal, Quebec, Canada
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Asamoah B, Khatoun A, Mc Laughlin M. Frequency-Specific Modulation of Slow-Wave Neural Oscillations via Weak Exogeneous Extracellular Fields Reveals a Resonance Pattern. J Neurosci 2022; 42:6221-6231. [PMID: 35790404 PMCID: PMC9374140 DOI: 10.1523/jneurosci.0177-22.2022] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2022] [Revised: 04/18/2022] [Accepted: 05/10/2022] [Indexed: 11/21/2022] Open
Abstract
Single neurons often exhibit endogenous oscillatory activity centered around a specific frequency band. Transcranial alternating current stimulation (tACS) can generate a weak oscillating extracellular field in the brain that causes subthreshold membrane potential shifts that can affect spike timing at the single neuron level. Many studies have now shown that the endogenous oscillation can be entrained when the tACS frequency matches that of the exogenous extracellular field. However, the effect of tACS on the amplitude of the endogenous oscillation has been less well studied. We investigated this by using exogenous extracellular fields to modulate slow-wave neural oscillations in the ketamine anesthetized male Wistar rat. We applied spatially broad extracellular fields of different frequencies while recording spiking activity from single neurons. The effect of the exogenous extracellular field on the slow-wave neural oscillation amplitude (NOA) followed a resonance pattern: large modulations were observed when the extracellular frequency matched the endogenous frequency of the neuron, while extracellular fields with frequencies far away from the endogenous frequency had little effect. No changes in spike-rate were observed for any of the extracellular fields applied. Our results demonstrate that in addition to the previously reported entrainment and Arnold tongue patterns, weak oscillating extracellular fields modulate the amplitude of the endogenous neural oscillation without any changes in spike-rate, and that this modulation follows a frequency-specific resonance pattern.SIGNIFICANCE STATEMENT Neural activity often oscillates around specific endogenous frequencies. Transcranial alternating current stimulation (tACS) is a neuromodulation method which biases spike-times and alter endogenous activity. Most tACS studies focus on entrainment effects which occur when tACS and endogenous neural frequencies are matched. In this study we varied the frequency of the applied tACS and investigated its effect on amplitude of the neural oscillation. Our results revealed a resonance pattern where tACS frequencies close to the endogenous frequency caused an increase in neural oscillation amplitude (NOA) specifically at the applied tACS frequency, while applying tACS frequencies farther away caused little or no change in NOA. Furthermore, applying tACS at differing frequencies caused the amplitude of the neural oscillation at the prestimulation endogenous frequency to decrease.
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Affiliation(s)
- Boateng Asamoah
- ExpORL, Department of neurosciences, The Leuven Brain Institute, Katholieke Universiteit Leuven, Leuven B-3000, Belgium
| | - Ahmad Khatoun
- ExpORL, Department of neurosciences, The Leuven Brain Institute, Katholieke Universiteit Leuven, Leuven B-3000, Belgium
| | - Myles Mc Laughlin
- ExpORL, Department of neurosciences, The Leuven Brain Institute, Katholieke Universiteit Leuven, Leuven B-3000, Belgium
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Armstrong SR, Bland NS, Sale MV, Cunnington R. Unconscious Influences on "Free Will" Movement Initiation: Slow-wave Brain Stimulation and the Readiness Potential. J Cogn Neurosci 2022; 34:1038-1052. [PMID: 35195727 DOI: 10.1162/jocn_a_01840] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/04/2022]
Abstract
A central objective in the study of volition has been to identify how changes in neural activity relate to voluntary-"free will"-movement. The readiness potential (RP) is observed in the EEG as a slow-building signal that precedes action onset. Many consider the RP as a marker of an underlying preparatory process for initiating voluntary movement. However, the RP may emerge from ongoing slow-wave brain oscillations that influence the timing of movement initiation in a phase-dependent manner. Transcranial alternating current stimulation (tACS) enables brain oscillations to be entrained at the frequency of stimulation. We delivered tACS at a slow-wave frequency over frontocentral motor areas while participants (n = 30) performed a simple, self-paced button press task. During the active tACS condition, participants showed a tendency to initiate actions in the phase of the tACS cycle that corresponded to increased negative potentials across the frontocentral motor region. Comparisons of premovement EEG activity observed over frontocentral and central scalp electrodes showed earlier onset and increased amplitude of RPs from active stimulation compared with sham stimulation. This suggests that movement-related activity in the brain can be modulated by the delivery of weak, nonconsciously perceptible alternating currents over frontocentral motor regions. We present novel findings that support existing theories, which suggest the timing of voluntary movement is influenced by the phase of slow-changing oscillating brain states.
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Khatoun A, Asamoah B, Mc Laughlin M. A Computational Modeling Study to Investigate the Use of Epicranial Electrodes to Deliver Interferential Stimulation to Subcortical Regions. Front Neurosci 2022; 15:779271. [PMID: 34975383 PMCID: PMC8716464 DOI: 10.3389/fnins.2021.779271] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2021] [Accepted: 11/29/2021] [Indexed: 11/16/2022] Open
Abstract
Background: Epicranial cortical stimulation (ECS) is a minimally invasive neuromodulation technique that works by passing electric current between subcutaneous electrodes positioned on the skull. ECS causes a stronger and more focused electric field in the cortex compared to transcranial electric stimulation (TES) where the electrodes are placed on the scalp. However, it is unknown if ECS can target deeper regions where the electric fields become relatively weak and broad. Recently, interferential stimulation (IF) using scalp electrodes has been proposed as a novel technique to target subcortical regions. During IF, two high, but slightly different, frequencies are applied which sum to generate a low frequency field (i.e., 10 Hz) at a target subcortical region. We hypothesized that IF using ECS electrodes would cause stronger and more focused subcortical stimulation than that using TES electrodes. Objective: Use computational modeling to determine if interferential stimulation-epicranial cortical stimulation (IF-ECS) can target subcortical regions. Then, compare the focality and field strength of IF-ECS to that of interferential Stimulation-transcranial electric stimulation (IF-TES) in the same subcortical region. Methods: A human head computational model was developed with 19 TES and 19 ECS disk electrodes positioned on a 10–20 system. After tetrahedral mesh generation the model was imported to COMSOL where the electric field distribution was calculated for each electrode separately. Then in MATLAB, subcortical targets were defined and the optimal configurations were calculated for both the TES and ECS electrodes. Results: Interferential stimulation using ECS electrodes can deliver stronger and more focused electric fields to subcortical regions than IF using TES electrodes. Conclusion: Interferential stimulation combined with ECS is a promising approach for delivering subcortical stimulation without the need for a craniotomy.
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Affiliation(s)
- Ahmad Khatoun
- ExpORL, Department of Neurosciences, KU Leuven, Leuven, Belgium.,The Leuven Brain Institute, KU Leuven, Leuven, Belgium
| | - Boateng Asamoah
- ExpORL, Department of Neurosciences, KU Leuven, Leuven, Belgium.,The Leuven Brain Institute, KU Leuven, Leuven, Belgium
| | - Myles Mc Laughlin
- ExpORL, Department of Neurosciences, KU Leuven, Leuven, Belgium.,The Leuven Brain Institute, KU Leuven, Leuven, Belgium
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Wu L, Liu T, Wang J. Improving the Effect of Transcranial Alternating Current Stimulation (tACS): A Systematic Review. Front Hum Neurosci 2021; 15:652393. [PMID: 34163340 PMCID: PMC8215166 DOI: 10.3389/fnhum.2021.652393] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2021] [Accepted: 04/26/2021] [Indexed: 11/15/2022] Open
Abstract
With the development of electrical stimulation technology, traditional transcranial alternating current stimulation (tACS) technology has been found to have the drawback of not targeting a specific area accurately. Studies have shown that optimizing the number and position of electrodes during electrical stimulation has a very good effect on enhancing brain stimulation accuracy. At present, an increasing number of laboratories have begun to optimize tACS. However, there has been no study summarizing the optimization methods of tACS. Determining whether different optimization methods are effective and the optimization approach could provide information that could guide future tACS research. We describe the results of recent research on tACS optimization and integrate the optimization approaches of tACS in recent research. Optimization approaches can be classified into two groups: high-definition electrical stimulation and interference modulation electrical stimulation. The optimization methods can be divided into five categories: high-definition tACS, phase-shifted tACS, amplitude-modulated tACS, the temporally interfering (TI) method, and the intersectional short pulse (ISP) method. Finally, we summarize the latest research on hardware useful for tACS improvement and outline future directions.
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Affiliation(s)
- Linyan Wu
- The Key Laboratory of Biomedical Information Engineering of Ministry of Education, Institute of Health and Rehabilitation Science, School of Life Science and Technology, Xi'an Jiaotong University, Xi'an, China.,National Engineering Research Center of Health Care and Medical Devices, Guangzhou, China.,The Key Laboratory of Neuro-informatics & Rehabilitation Engineering of Ministry of Civil Affairs, Xi'an, China
| | - Tian Liu
- The Key Laboratory of Biomedical Information Engineering of Ministry of Education, Institute of Health and Rehabilitation Science, School of Life Science and Technology, Xi'an Jiaotong University, Xi'an, China.,National Engineering Research Center of Health Care and Medical Devices, Guangzhou, China.,The Key Laboratory of Neuro-informatics & Rehabilitation Engineering of Ministry of Civil Affairs, Xi'an, China
| | - Jue Wang
- The Key Laboratory of Biomedical Information Engineering of Ministry of Education, Institute of Health and Rehabilitation Science, School of Life Science and Technology, Xi'an Jiaotong University, Xi'an, China.,National Engineering Research Center of Health Care and Medical Devices, Guangzhou, China.,The Key Laboratory of Neuro-informatics & Rehabilitation Engineering of Ministry of Civil Affairs, Xi'an, China
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7
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van der Plas M, Wang D, Brittain JS, Hanslmayr S. Investigating the role of phase-synchrony during encoding of episodic memories using electrical stimulation. Cortex 2020; 133:37-47. [PMID: 33099074 DOI: 10.1016/j.cortex.2020.09.006] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2020] [Revised: 06/03/2020] [Accepted: 09/15/2020] [Indexed: 01/15/2023]
Abstract
The multi-sensory nature of episodic memories indicates that communication between a multitude of brain areas is required for their effective creation and recollection. Previous studies have suggested that the effectiveness of memory processes depends on theta synchronization (4 Hz) of sensory areas relevant to the memory. This study aimed to manipulate theta synchronization between different sensory areas in order to further test this hypothesis. We intend to entrain visual cortex with 4 Hz alternating current stimulation (tACS), while simultaneously entraining auditory cortex with 4 Hz amplitude-modulated sounds. By entraining these different sensory areas, which pertain to learned audio-visual memory associations, we expect to find that when theta is synchronized across the different sensory areas, the memory performance would be enhanced compared to when theta is not synchronized across the sensory areas. We found no evidence for such an effect in this study. It is unclear whether this is due to an inability of 4 Hz tACS to entrain the visual cortex reliably, or whether sensory entrainment is not the underlying mechanism required for episodic memory.
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Affiliation(s)
- Mircea van der Plas
- School of Psychology, University of Birmingham, Edgbaston, Birmingham, United Kingdom; Centre for Human Brain Health, University of Birmingham, Edgbaston, Birmingham, United Kingdom; Centre for Cognitive Neuroimaging, University of Glasgow, Glasgow, United Kingdom
| | - Danying Wang
- School of Psychology, University of Birmingham, Edgbaston, Birmingham, United Kingdom; Centre for Human Brain Health, University of Birmingham, Edgbaston, Birmingham, United Kingdom; Centre for Cognitive Neuroimaging, University of Glasgow, Glasgow, United Kingdom
| | - John-Stuart Brittain
- School of Psychology, University of Birmingham, Edgbaston, Birmingham, United Kingdom; Centre for Human Brain Health, University of Birmingham, Edgbaston, Birmingham, United Kingdom
| | - Simon Hanslmayr
- School of Psychology, University of Birmingham, Edgbaston, Birmingham, United Kingdom; Centre for Human Brain Health, University of Birmingham, Edgbaston, Birmingham, United Kingdom; Centre for Cognitive Neuroimaging, University of Glasgow, Glasgow, United Kingdom.
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Vieira PG, Krause MR, Pack CC. tACS entrains neural activity while somatosensory input is blocked. PLoS Biol 2020; 18:e3000834. [PMID: 33001971 PMCID: PMC7553316 DOI: 10.1371/journal.pbio.3000834] [Citation(s) in RCA: 42] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2020] [Revised: 10/13/2020] [Accepted: 09/01/2020] [Indexed: 02/06/2023] Open
Abstract
Transcranial alternating current stimulation (tACS) modulates brain activity by passing electrical current through electrodes that are attached to the scalp. Because it is safe and noninvasive, tACS holds great promise as a tool for basic research and clinical treatment. However, little is known about how tACS ultimately influences neural activity. One hypothesis is that tACS affects neural responses directly, by producing electrical fields that interact with the brain’s endogenous electrical activity. By controlling the shape and location of these electric fields, one could target brain regions associated with particular behaviors or symptoms. However, an alternative hypothesis is that tACS affects neural activity indirectly, via peripheral sensory afferents. In particular, it has often been hypothesized that tACS acts on sensory fibers in the skin, which in turn provide rhythmic input to central neurons. In this case, there would be little possibility of targeted brain stimulation, as the regions modulated by tACS would depend entirely on the somatosensory pathways originating in the skin around the stimulating electrodes. Here, we directly test these competing hypotheses by recording single-unit activity in the hippocampus and visual cortex of alert monkeys receiving tACS. We find that tACS entrains neuronal activity in both regions, so that cells fire synchronously with the stimulation. Blocking somatosensory input with a topical anesthetic does not significantly alter these neural entrainment effects. These data are therefore consistent with the direct stimulation hypothesis and suggest that peripheral somatosensory stimulation is not required for tACS to entrain neurons. Transcranial alternating current stimulation (tACS) modulates brain activity by passing electrical current through electrodes that are attached to the scalp. However, whereas one hypothesis is that tACS affects neural responses directly, another is that tACS affects neural activity indirectly, via sensory fibers in the skin. This study demonstrates that tACS directly affects neurons within the brain, rather than relying on a peripheral route.
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Affiliation(s)
- Pedro G. Vieira
- Department of Neurology and Neurosurgery, McGill University, Montreal, Quebec, Canada
| | - Matthew R. Krause
- Department of Neurology and Neurosurgery, McGill University, Montreal, Quebec, Canada
| | - Christopher C. Pack
- Department of Neurology and Neurosurgery, McGill University, Montreal, Quebec, Canada
- * E-mail:
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9
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Bergmann TO, Hartwigsen G. Inferring Causality from Noninvasive Brain Stimulation in Cognitive Neuroscience. J Cogn Neurosci 2020; 33:195-225. [PMID: 32530381 DOI: 10.1162/jocn_a_01591] [Citation(s) in RCA: 97] [Impact Index Per Article: 24.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Noninvasive brain stimulation (NIBS) techniques, such as transcranial magnetic stimulation or transcranial direct and alternating current stimulation, are advocated as measures to enable causal inference in cognitive neuroscience experiments. Transcending the limitations of purely correlative neuroimaging measures and experimental sensory stimulation, they allow to experimentally manipulate brain activity and study its consequences for perception, cognition, and eventually, behavior. Although this is true in principle, particular caution is advised when interpreting brain stimulation experiments in a causal manner. Research hypotheses are often oversimplified, disregarding the underlying (implicitly assumed) complex chain of causation, namely, that the stimulation technique has to generate an electric field in the brain tissue, which then evokes or modulates neuronal activity both locally in the target region and in connected remote sites of the network, which in consequence affects the cognitive function of interest and eventually results in a change of the behavioral measure. Importantly, every link in this causal chain of effects can be confounded by several factors that have to be experimentally eliminated or controlled to attribute the observed results to their assumed cause. This is complicated by the fact that many of the mediating and confounding variables are not directly observable and dose-response relationships are often nonlinear. We will walk the reader through the chain of causation for a generic cognitive neuroscience NIBS study, discuss possible confounds, and advise appropriate control conditions. If crucial assumptions are explicitly tested (where possible) and confounds are experimentally well controlled, NIBS can indeed reveal cause-effect relationships in cognitive neuroscience studies.
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Affiliation(s)
| | - Gesa Hartwigsen
- Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany
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Lefebvre S, Jann K, Schmiesing A, Ito K, Jog M, Schweighofer N, Wang DJJ, Liew SL. Differences in high-definition transcranial direct current stimulation over the motor hotspot versus the premotor cortex on motor network excitability. Sci Rep 2019; 9:17605. [PMID: 31772347 PMCID: PMC6879500 DOI: 10.1038/s41598-019-53985-7] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2019] [Accepted: 11/06/2019] [Indexed: 01/07/2023] Open
Abstract
The effectiveness of transcranial direct current stimulation (tDCS) placed over the motor hotspot (thought to represent the primary motor cortex (M1)) to modulate motor network excitability is highly variable. The premotor cortex-particularly the dorsal premotor cortex (PMd)-may be a promising alternative target to reliably modulate motor excitability, as it influences motor control across multiple pathways, one independent of M1 and one with direct connections to M1. This double-blind, placebo-controlled preliminary study aimed to differentially excite motor and premotor regions using high-definition tDCS (HD-tDCS) with concurrent functional magnetic resonance imaging (fMRI). HD-tDCS applied over either the motor hotspot or the premotor cortex demonstrated high inter-individual variability in changes on cortical motor excitability. However, HD-tDCS over the premotor cortex led to a higher number of responders and greater changes in local fMRI-based complexity than HD-tDCS over the motor hotspot. Furthermore, an analysis of individual motor hotspot anatomical locations revealed that, in more than half of the participants, the motor hotspot is not located over anatomical M1 boundaries, despite using a canonical definition of the motor hotspot. This heterogeneity in stimulation site may contribute to the variability of tDCS results. Altogether, these preliminary findings provide new considerations to enhance tDCS reliability.
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Affiliation(s)
- Stephanie Lefebvre
- Neural Plasticity and Neurorehabilitation Laboratory, Chan Division of Occupational Science and Occupational Therapy, University of Southern California, Los Angeles, CA, United States
| | - Kay Jann
- Laboratory of FMRI Technology (LOFT), USC Stevens Neuroimaging and Informatics Institute, Keck School of Medicine of USC, University of Southern California, Los Angeles, CA, USA
- Laboratory of Neuro Imaging (LONI), USC Stevens Neuroimaging and Informatics Institute, Keck School of Medicine of USC, University of Southern California, Los Angeles, CA, USA
| | - Allie Schmiesing
- Neural Plasticity and Neurorehabilitation Laboratory, Chan Division of Occupational Science and Occupational Therapy, University of Southern California, Los Angeles, CA, United States
| | - Kaori Ito
- Neural Plasticity and Neurorehabilitation Laboratory, Chan Division of Occupational Science and Occupational Therapy, University of Southern California, Los Angeles, CA, United States
| | - Mayank Jog
- Laboratory of FMRI Technology (LOFT), USC Stevens Neuroimaging and Informatics Institute, Keck School of Medicine of USC, University of Southern California, Los Angeles, CA, USA
- Laboratory of Neuro Imaging (LONI), USC Stevens Neuroimaging and Informatics Institute, Keck School of Medicine of USC, University of Southern California, Los Angeles, CA, USA
| | - Nicolas Schweighofer
- Division of Biokinesiology and Physical Therapy, University of Southern California, Los Angeles, CA, USA
| | - Danny J J Wang
- Laboratory of FMRI Technology (LOFT), USC Stevens Neuroimaging and Informatics Institute, Keck School of Medicine of USC, University of Southern California, Los Angeles, CA, USA
- Laboratory of Neuro Imaging (LONI), USC Stevens Neuroimaging and Informatics Institute, Keck School of Medicine of USC, University of Southern California, Los Angeles, CA, USA
| | - Sook-Lei Liew
- Neural Plasticity and Neurorehabilitation Laboratory, Chan Division of Occupational Science and Occupational Therapy, University of Southern California, Los Angeles, CA, United States.
- Laboratory of Neuro Imaging (LONI), USC Stevens Neuroimaging and Informatics Institute, Keck School of Medicine of USC, University of Southern California, Los Angeles, CA, USA.
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11
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Bland NS, Sale MV. Current challenges: the ups and downs of tACS. Exp Brain Res 2019; 237:3071-3088. [DOI: 10.1007/s00221-019-05666-0] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2019] [Accepted: 10/09/2019] [Indexed: 02/08/2023]
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12
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Khatoun A, Asamoah B, Mc Laughlin M. Investigating the Feasibility of Epicranial Cortical Stimulation Using Concentric-Ring Electrodes: A Novel Minimally Invasive Neuromodulation Method. Front Neurosci 2019; 13:773. [PMID: 31396045 PMCID: PMC6667561 DOI: 10.3389/fnins.2019.00773] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2018] [Accepted: 07/10/2019] [Indexed: 01/26/2023] Open
Abstract
Background Invasive cortical stimulation (ICS) is a neuromodulation method in which electrodes are implanted on the cortex to deliver chronic stimulation. ICS has been used to treat neurological disorders such as neuropathic pain, epilepsy, movement disorders and tinnitus. Noninvasive neuromodulation methods such as transcranial magnetic stimulation and transcranial electrical stimulation (TES) show great promise in treating some neurological disorders and require no surgery. However, only acute stimulation can be delivered. Epicranial current stimulation (ECS) is a novel concept for delivering chronic neuromodulation through subcutaneous electrodes implanted on the skull. The use of concentric-ring ECS electrodes may allow spatially focused stimulation and offer a less invasive alternative to ICS. Objectives Demonstrate ECS proof-of-concept using concentric-ring electrodes in rats and then use a computational model to explore the feasibility and limitations of ECS in humans. Methods ECS concentric-ring electrodes were implanted in 6 rats and pulsatile stimulation delivered to the motor cortex. An MRI based electro-anatomical human head model was used to explore different ECS concentric-ring electrode designs and these were compared with ICS and TES. Results Concentric-ring ECS electrodes can selectively stimulate the rat motor cortex. The computational model showed that the concentric-ring ECS electrode design can be optimized to achieve focused cortical stimulation. In general, focality was less than ICS but greater than noninvasive transcranial current stimulation. Conclusion ECS could be a promising minimally invasive alternative to ICS. Further work in large animal models and patients is needed to demonstrate feasibility and long-term stability.
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Affiliation(s)
- Ahmad Khatoun
- Research Group Experimental Oto-Rhino-Laryngology (ExpORL), Department of Neurosciences, KU Leuven, Leuven, Belgium.,The Leuven Brain Institute, KU Leuven, Leuven, Belgium
| | - Boateng Asamoah
- Research Group Experimental Oto-Rhino-Laryngology (ExpORL), Department of Neurosciences, KU Leuven, Leuven, Belgium.,The Leuven Brain Institute, KU Leuven, Leuven, Belgium
| | - Myles Mc Laughlin
- Research Group Experimental Oto-Rhino-Laryngology (ExpORL), Department of Neurosciences, KU Leuven, Leuven, Belgium.,The Leuven Brain Institute, KU Leuven, Leuven, Belgium
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13
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S S, Sriram K. Hilbert transform-based time-series analysis of the circadian gene regulatory network. IET Syst Biol 2019; 13:159-168. [PMID: 31318333 PMCID: PMC8687344 DOI: 10.1049/iet-syb.2018.5088] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
In this work, the authors propose the Hilbert transform (HT)‐based numerical method to analyse the time series of the circadian rhythms. They demonstrate the application of HT by taking both deterministic and stochastic time series that they get from the simulation of the fruit fly model Drosophila melanogaster and show how to extract the period, construct phase response curves, determine period sensitivity of the parameters to perturbations and build Arnold tongues to identify the regions of entrainment. They also derive a phase model that they numerically simulate to capture whether the circadian time series entrains to the forcing period completely (phase locking) or only partially (phase slips) or neither. They validate the phase model, and numerics with the experimental time series forced under different temperature cycles. Application of HT to the circadian time series appears to be a promising tool to extract the characteristic information about circadian rhythms.
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Affiliation(s)
- Shiju S
- Center for Computational Biology, Indraprastha Institute of Information Technology Delhi, New Delhi 110020, India
| | - K Sriram
- Center for Computational Biology, Indraprastha Institute of Information Technology Delhi, New Delhi 110020, India.
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14
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Asamoah B, Khatoun A, Mc Laughlin M. Analytical bias accounts for some of the reported effects of tACS on auditory perception. Brain Stimul 2019; 12:1001-1009. [PMID: 30930210 DOI: 10.1016/j.brs.2019.03.011] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2018] [Revised: 03/08/2019] [Accepted: 03/12/2019] [Indexed: 12/12/2022] Open
Abstract
BACKGROUND Transcranial alternating current stimulation (tACS) has been shown to modulate auditory, visual, cognitive and motor function. However, tACS effects can often be small and difficult to reproduce. Thus, the establishment of robust experimental and analysis procedures is of high importance. We reviewed the analysis used in six studies that investigated if tACS can phase-modulate auditory perception. All studies used analytical methods that introduce bias and could produce false positive results. Four studies corrected for this bias but two did not. OBJECTIVE Our objectives were two-fold: 1) Use simulated null hypothesis datasets, where no tACS effect is present, to determine if uncorrected analytical bias could account for some of the reported effects on auditory perception. 2) Help establish best practices to correct for bias when analyzing tACS phase-effects on perception. METHODS We simulated null hypothesis datasets (i.e. no tACS effect) by drawing samples for all tACS and sham conditions from the same normal distribution. We then applied the reported analyses to the null hypothesis datasets. RESULTS Reported results from studies that did not correct for analytical bias could be reproduced from the null hypothesis datasets. However, results for studies that did correct for analytical bias could not be reproduced from the null hypothesis datasets. CONCLUSION True effects of tACS on auditory perception can be detected if analytical bias is accounted for by using correction procedures. However, to fully establish the effects of tACS on auditory perception a reanalysis of the data for the studies that used biased analysis without correction procedures is needed.
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Affiliation(s)
- Boateng Asamoah
- Exp ORL, Department of Neurosciences, The Leuven Brain Institute, KU Leuven, B-3000, Leuven, Belgium.
| | - Ahmad Khatoun
- Exp ORL, Department of Neurosciences, The Leuven Brain Institute, KU Leuven, B-3000, Leuven, Belgium.
| | - Myles Mc Laughlin
- Exp ORL, Department of Neurosciences, The Leuven Brain Institute, KU Leuven, B-3000, Leuven, Belgium.
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15
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Karabanov AN, Saturnino GB, Thielscher A, Siebner HR. Can Transcranial Electrical Stimulation Localize Brain Function? Front Psychol 2019; 10:213. [PMID: 30837911 PMCID: PMC6389710 DOI: 10.3389/fpsyg.2019.00213] [Citation(s) in RCA: 36] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2018] [Accepted: 01/22/2019] [Indexed: 11/13/2022] Open
Abstract
Transcranial electrical stimulation (TES) uses constant (TDCS) or alternating currents (TACS) to modulate brain activity. Most TES studies apply low-intensity currents through scalp electrodes (≤2 mA) using bipolar electrode arrangements, producing weak electrical fields in the brain (<1 V/m). Low-intensity TES has been employed in humans to induce changes in task performance during or after stimulation. In analogy to focal transcranial magnetic stimulation, TES-induced behavioral effects have often been taken as evidence for a causal involvement of the brain region underlying one of the two stimulation electrodes, often referred to as the active electrode. Here, we critically review the utility of bipolar low-intensity TES to localize human brain function. We summarize physiological substrates that constitute peripheral targets for TES and may mediate subliminal or overtly perceived peripheral stimulation during TES. We argue that peripheral co-stimulation may contribute to the behavioral effects of TES and should be controlled for by "sham" TES. We discuss biophysical properties of TES, which need to be considered, if one wishes to make realistic assumptions about which brain regions were preferentially targeted by TES. Using results from electric field calculations, we evaluate the validity of different strategies that have been used for selective spatial targeting. Finally, we comment on the challenge of adjusting the dose of TES considering dose-response relationships between the weak tissue currents and the physiological effects in targeted cortical areas. These considerations call for caution when attributing behavioral effects during or after low-intensity TES studies to a specific brain region and may facilitate the selection of best practices for future TES studies.
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Affiliation(s)
- Anke Ninija Karabanov
- Danish Research Centre for Magnetic Resonance, Centre for Functional and Diagnostic Imaging and Research, Copenhagen University Hospital Hvidovre, Hvidovre, Denmark
| | - Guilherme Bicalho Saturnino
- Danish Research Centre for Magnetic Resonance, Centre for Functional and Diagnostic Imaging and Research, Copenhagen University Hospital Hvidovre, Hvidovre, Denmark
- Department of Electrical Engineering, Technical University of Denmark, Copenhagen, Denmark
| | - Axel Thielscher
- Danish Research Centre for Magnetic Resonance, Centre for Functional and Diagnostic Imaging and Research, Copenhagen University Hospital Hvidovre, Hvidovre, Denmark
- Department of Electrical Engineering, Technical University of Denmark, Copenhagen, Denmark
| | - Hartwig Roman Siebner
- Danish Research Centre for Magnetic Resonance, Centre for Functional and Diagnostic Imaging and Research, Copenhagen University Hospital Hvidovre, Hvidovre, Denmark
- Department of Neurology, Copenhagen University Hospital Bispebjerg, Copenhagen, Denmark
- Institute for Clinical Medicine, Faculty of Health Sciences and Medicine, University of Copenhagen, Copenhagen, Denmark
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16
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Asamoah B, Khatoun A, Mc Laughlin M. tACS motor system effects can be caused by transcutaneous stimulation of peripheral nerves. Nat Commun 2019; 10:266. [PMID: 30655523 PMCID: PMC6336776 DOI: 10.1038/s41467-018-08183-w] [Citation(s) in RCA: 136] [Impact Index Per Article: 27.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2018] [Accepted: 12/19/2018] [Indexed: 01/19/2023] Open
Abstract
Transcranial alternating current stimulation (tACS) is a noninvasive neuromodulation method which has been shown to modulate hearing, motor, cognitive and memory function. However, the mechanisms underpinning these findings are controversial, as studies show that the current reaching the cortex may not be strong enough to entrain neural activity. Here, we propose a new hypothesis to reconcile these opposing results: tACS effects are caused by transcutaneous stimulation of peripheral nerves in the skin and not transcranial stimulation of cortical neurons. Rhythmic activity from peripheral nerves then entrains cortical neurons. A series of experiments in rats and humans isolated the transcranial and transcutaneous mechanisms and showed that the reported effects of tACS on the motor system can be caused by transcutaneous stimulation of peripheral nerves. Whether or not the transcutaneous mechanism will generalize to tACS effects on other systems is debatable but should be investigated. Transcranial alternating current stimulation (tACS) uses weak electrical currents, applied to the head, to modulate brain activity. Here, the authors show that contrary to previous assumptions, the effects of tACS on the brain may be mediated by its effect on peripheral nerves in the skin, not direct.
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Affiliation(s)
- Boateng Asamoah
- Exp ORL, Department of Neurosciences, KU Leuven, B-3000, Leuven, Belgium
| | - Ahmad Khatoun
- Exp ORL, Department of Neurosciences, KU Leuven, B-3000, Leuven, Belgium
| | - Myles Mc Laughlin
- Exp ORL, Department of Neurosciences, KU Leuven, B-3000, Leuven, Belgium.
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17
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Armstrong S, Sale MV, Cunnington R. Neural Oscillations and the Initiation of Voluntary Movement. Front Psychol 2018; 9:2509. [PMID: 30618939 PMCID: PMC6307533 DOI: 10.3389/fpsyg.2018.02509] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2018] [Accepted: 11/26/2018] [Indexed: 12/26/2022] Open
Abstract
The brain processes involved in the planning and initiation of voluntary action are of great interest for understanding the relationship between conscious awareness of decisions and the neural control of movement. Voluntary motor behavior has generally been considered to occur when conscious decisions trigger movements. However, several studies now provide compelling evidence that brain states indicative of forthcoming movements take place before a person becomes aware of a conscious decision to act. While such studies have created much debate over the nature of ‘free will,’ at the very least they suggest that unconscious brain processes are predictive of forthcoming movements. Recent studies suggest that slow changes in neuroelectric potentials may play a role in the timing of movement onset by pushing brain activity above a threshold to trigger the initiation of action. Indeed, recent studies have shown relationships between the phase of low frequency oscillatory activity of the brain and the onset of voluntary action. Such studies, however, cannot determine whether this underlying neural activity plays a causal role in the initiation of movement or is only associated with the intentional behavior. Non-invasive transcranial alternating current brain stimulation can entrain neural activity at particular frequencies in order to assess whether underlying brain processes are causally related to associated behaviors. In this review, we examine the evidence for neural coding of action as well as the brain states prior to action initiation and discuss whether low frequency alternating current brain stimulation could influence the timing of a persons’ decision to act.
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Affiliation(s)
- Samuel Armstrong
- Queensland Brain Institute, The University of Queensland, Brisbane, QLD, Australia
| | - Martin V Sale
- Queensland Brain Institute, The University of Queensland, Brisbane, QLD, Australia.,School of Health and Rehabilitation Sciences, The University of Queensland, Brisbane, QLD, Australia
| | - Ross Cunnington
- Queensland Brain Institute, The University of Queensland, Brisbane, QLD, Australia.,School of Psychology, The University of Queensland, Brisbane, QLD, Australia
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