Transcranial oscillatory stimulation of peripheral nerves in the skin entrains physiological tremor in healthy volunteers.
Summery
Transcranial alternating current stimulation (tACS) is a noninvasive neuromodulation technique that alter perception, cognition, and motor function. The mechanism by which tACS causes such effects is controversial. A transcranial mechanism is widely assumed. However, recent evidence shows that the field in the cortex is too weak to entrain neurons. We hypothesized that reported tACS effects may be caused by transcutaneous stimulation of peripheral nerves in the scalp. To test this hypothesis we separated the two mechanisms and studied the effect of each of them separately on entraining physiological tremor. We found that tACS effects are induced by the transcutaneous mechanism.
Introduction
Transcranial alternating current stimulation (tACS) is a noninvasive neuromodulation technique that can alter perception, cognition, motor function and entrain physiological tremor in healthy volunteers[ 1]. The mechanism by which tACS causes such effects is controversial. A transcranial mechanism is widely assumed, i.e. the weak electric field in the brain modulates cortical neurons directly. However, recent evidence shows that the field in the cortex is too weak to entrain neurons. We hypothesized that reported tACS effects may be caused by transcutaneous stimulation of peripheral nerves in the scalp.
Methods
To test this, we measured the effect of tACS on physiological tremor in healthy volunteers under two experimental conditions. Tremor was measured using an accelerometer. tACS was applied at three amplitudes: 0 mA, 0.5 mA and 2.5 mA. The phase lock value (PLV) between the tremor and tACS was calculated to quantify entrainment.
In Experiment 1 (n=12) HD-tACS was applied to the motor cortex. The transcutaneous mechanism was blocked by applying topical anesthetic to the scalp. A blinded, randomized, cross-over design was used to test the effects of blocking the transcutaneous mechanism.
In Experiment 2 (n=10) the tACS electrodes were moved to the arm contralateral to tremor measurement, effectively blocking the transcranial mechanism.
Results
In Experiment 1, we found that anesthetizing the scalp caused a significant reduction in tremor entrainment. In Experiment 2, we found that placing the tACS electrode on the contralateral arm still caused significant tremor entrainment.
Conclusion
Our results show that the transcutaneous, and not the transcranial, mechanism cause tACS motor system effects.
Acknowledgements
This work was supported by: KU Leuven Research Funding STG/14/024 and EGM-D2929-C24/17/091, EIT Health Innovation by Ideas, NEURO-WEAR Project. Boateng Asamoah is SB PhD fellow at FWO.
References
[1] Khatoun, Ahmad, Breukers, Jolien, Op De Beeck, Sara, Nica, Ioana Gabriela, Aerts, Jean-Marie, Seynaeve, Laura, Haeck, Tom, Asamoah, Boateng, and Mc Laughlin, Myles. "Using High-amplitude and Focused Transcranial Alternating Current Stimulation to Entrain Physiological Tremor." Scientific Reports 8, no. 1 (2018): Scientific Reports; 2018; Vol. 8; Iss. 1; Pp.
Keywords:
tACS (transcranial alternating current stimulation),
tDCS — transcranial direct current stimulation,
peripheral nerve stimulation,
Tremor,
Mechanism
Conference:
Belgian Brain Congress 2018 — Belgian Brain Council, LIEGE, Belgium, 19 Oct - 19 Oct, 2018.
Presentation Type:
e-posters
Topic:
NOVEL STRATEGIES FOR NEUROLOGICAL AND MENTAL DISORDERS: SCIENTIFIC BASIS AND VALUE FOR PATIENT-CENTERED CARE
Citation:
Khatoun
A,
Asamoah
B and
Mc Laughlin
M
(2019). Transcranial oscillatory stimulation of peripheral nerves in the skin entrains physiological tremor in healthy volunteers..
Front. Neurosci.
Conference Abstract:
Belgian Brain Congress 2018 — Belgian Brain Council.
doi: 10.3389/conf.fnins.2018.95.00077
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Received:
30 Aug 2018;
Published Online:
17 Jan 2019.
*
Correspondence:
Mr. Ahmad Khatoun, KU Leuven, Leuven, Belgium, ahmad.khatoun@kuleuven.be