Proceedings of The Physiological Society

Future Physiology (Leeds, UK) (2017) Proc Physiol Soc 39, PC08

Poster Communications

Identifying neural drive to arm muscles using Transcranial Magnetic Stimulation and Transmastoid Electrical Stimulation

T. C. RICHARDS1, A. Desai2, S. Astill1, K. Power3, S. Chakrabarty1

1. Faculty of Biological Sciences, University of Leeds, Leeds, West Yorkshire, United Kingdom. 2. Department of Electronics and Electrical Engineering, BITS Pilani, Goa, KK Birla, United Kingdom. 3. School of Human Kinetics and Recreation, Memorial University, St. Johns, Newfoundland, United Kingdom.

Cortico-muscular and intermuscular coherence studies have sought to relate activity in the sensorimotor cortex to activity in the muscle, or to identify muscles sharing common cortico-motoneuronal drive. Coherence is most commonly discussed in the context of three distinct bands: alpha (α) at 8 - 12 Hz, beta (β) at 15 - 30 Hz, and gamma (γ) at 30 - 100 Hz. Cortico-muscular coherence in the β-band is thought to reflect coupling of cortical oscillations to the spinal motoneuron pool during sustained contractions. Less commonly, coherence has been observed in the α-band, also during sustained contractions, and in the γ-band during dynamic movements. Cortico-muscular coherence within these bands is often assumed to reflect efferent activity of direct projections from the motor cortex to the spinal motoneurons. It has recently been demonstrated using TMS (transcranial magnetic stimulation) and TMES (transmastoid electrical stimulation) that cortical neuronal drive to the motoneurons of biceps brachii is altered during an arm cycling task compared to an intensity-matched tonic contraction (Forman et al., 2015). Here, a Continuous Wavelet Transform (CWT) is applied to this data to show changes in the frequency components of the EMG induced by different focal stimulation (n = 10). This allows us to assess the effects of different neuronal pathways on the associated EMG signal. We show that stimulation of the cortex during tonic contractions effects muscle firing below 60 Hz, whilst during the cycling task, frequencies up to 130 Hz are also effected. In the cycling task, this is most likely due to increased excitability of spinal or subcortical central pattern generator networks.

Where applicable, experiments conform with Society ethical requirements