Standard intensities of transcranial alternating current stimulation over the motor cortex do not entrain corticospinal inputs to motor neurons

Ibanez J, Zicher B, Brown KE, Rocchi L, Casolo A, Del Vecchio A, Spampinato D, Vollette CA, Rothwell JC, Baker SN, Farina D (2022)

Publication Type: Journal article

Publication year: 2022

Journal

The Journal of Physiology Wiley

DOI: 10.1113/JP282983

Abstract

Abstract: Transcranial alternating current stimulation (TACS) is commonly used to synchronize a cortical area and its outputs to the stimulus waveform, but gathering evidence for this based on brain recordings in humans is challenging. The corticospinal tract transmits beta oscillations (∼21 Hz) from the motor cortex to tonically contracted limb muscles linearly. Therefore, muscle activity may be used to measure the level of beta entrainment in the corticospinal tract due to TACS over the motor cortex. Here, we assessed whether TACS is able to modulate the neural inputs to muscles, which would provide indirect evidence for TACS-driven neural entrainment. In the first part of the study, we ran simulations of motor neuron (MN) pools receiving inputs from corticospinal neurons with different levels of beta entrainment. Results suggest that MNs are highly sensitive to changes in corticospinal beta activity. Then, we ran experiments on healthy human subjects (N = 10) in which TACS (at 1 mA) was delivered over the motor cortex at 21 Hz (beta stimulation), or at 7 Hz or 40 Hz (control conditions) while the abductor digiti minimi or the tibialis anterior muscle were tonically contracted. Muscle activity was measured using high-density electromyography, which allowed us to decompose the activity of pools of motor units innervating the muscles. By analysing motor unit pool activity, we observed that none of the TACS conditions could consistently alter the spectral contents of the common neural inputs received by the muscles. These results suggest that 1 mA TACS over the motor cortex given at beta frequencies does not entrain corticospinal activity. (Figure presented.). Key points: Transcranial alternating current stimulation (TACS) is commonly used to entrain the communication between brain regions. It is challenging to find direct evidence supporting TACS-driven neural entrainment due to the technical difficulties in recording brain activity during stimulation. Computational simulations of motor neuron pools receiving common inputs in the beta (∼21 Hz) band indicate that motor neurons are highly sensitive to corticospinal beta entrainment. Motor unit activity from human muscles does not support TACS-driven corticospinal entrainment.

Authors with CRIS profile

Alessandro Del Vecchio Juniorprofessur für Neuromuscular Physiology and Neural Interfacing

Involved external institutions

Universidad de Zaragoza ES Spain (ES) Imperial College London / The Imperial College of Science, Technology and Medicine GB United Kingdom (GB) University of Waterloo (UW) CA Canada (CA) University College London (UCL) GB United Kingdom (GB) University of Padua / Universita degli Studi di Padova IT Italy (IT) Fondazione Santa Lucia IRCCS IT Italy (IT) Institut national de physique nucléaire et de physique des particules (IN2P3) FR France (FR) Newcastle University GB United Kingdom (GB)

How to cite

APA:

Ibanez, J., Zicher, B., Brown, K.E., Rocchi, L., Casolo, A., Del Vecchio, A.,... Farina, D. (2022). Standard intensities of transcranial alternating current stimulation over the motor cortex do not entrain corticospinal inputs to motor neurons. The Journal of Physiology. https://doi.org/10.1113/JP282983

MLA:

Ibanez, Jaime, et al. "Standard intensities of transcranial alternating current stimulation over the motor cortex do not entrain corticospinal inputs to motor neurons." The Journal of Physiology (2022).

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