Proceedings of The Physiological Society

Physiology 2014 (London, UK) (2014) Proc Physiol Soc 31, PCB068

Poster Communications

Oscillatory power in human sensorimotor cortex during and following muscular contractions of distinct forces and rates of force development

A. Fry1, M. J. Brookes2, J. P. Folland1

1. School of Sport, Exercise & Health Sciences, Loughborough University, Loughborough, United Kingdom. 2. Sir Peter Mansfield Magnetic Resonance Centre, University of Nottingham, Nottingham, United Kingdom.

  • Figure 1. Averaged beta-band oscillatory power in the sensorimotor cortex during the plateau phase of the constant force contractions (A) and following the contractions (post-movement beta rebound; B) (n=15). Data are mean

  • Figure 2. Averaged beta-band oscillatory power in the sensorimotor cortex during the ramp phase of the ramp contractions (A) and following the contractions (post-movement beta rebound; B) (n=15). Data are mean

A decrease in beta-band (14-30 Hz) oscillatory power (β power) during voluntary muscular contractions, followed by a post-movement beta rebound (PMBR), are well established electrophysiological phenomena [1]. However, this pattern of oscillatory activity has been established in response to movements per se, with little attention directed to the kinetics of the muscle contractions responsible for movement. The aim of this study was to examine the effect of both contraction force and rate of force development (RFD) on β power measured using magnetoencephalography (MEG) during voluntary isometric contractions.Fifteen healthy volunteers (10 males, 2 left handed, age 23-40 years) undertook two experiments, both involving a series of 60 submaximal isometric contractions of the right wrist-flexors. Experiment 1: 15 constant force contractions of 3-s duration at each of four torque levels (5, 15, 35 & 60% maximal voluntary force (MVF)). Experiment 2: 20 ramp contractions at each of three RFDs (8.9, 26.7 & 80.0%MVF.s-1), where force was increased linearly from rest to 65%MVF in all contractions. During the experiments participants viewed a real-time graphical feedback of their contraction force overlaid on to a target force outline. MEG data (275 channels; 600 Hz) were coregistered to brain anatomy using a volumetric anatomical magnetic resonance image for each participant. Data were processed using synthetic aperture magnetometry (SAM) to localise stimulus driven change in β power, and trial averaged time-frequency spectrograms were then extracted from the derived sensorimotor cortex coordinates. Force and RFD effects on β power both during contractions (plateau phase of constant force contractions & ramp phase of ramp contractions) and post-contractions (~2 s following contraction completion) were explored using ANOVA (Fig. 1 & 2).Decreases in β power were modulated by RFD during the isometric ramp contractions (P=0.03; Fig. 2A), which could indicate that the drop in power may represent more than a simple removal of an idling beta rhythm. However, contraction force had no effect on β power during the constant force contractions (P=0.57; Fig. 1A). Post-contraction β power was greater following voluntary contractions of both higher forces (P=0.03; Fig. 1B) and higher RFDs (P=0.01; Fig. 2B). This might indicate a greater level of GABAergic inhibition in the sensorimotor cortex following stronger or faster contractions [2,3].In summary, decreases in β power during contraction were modulated by RFD, but not force, and post-contraction the extent of PMBR was greater for higher forces and RFDs. These findings enhance our understanding of how healthy brain function is related to voluntary muscular contraction kinetics, which has relevance to neurological disorders, brain-computer interfacing and healthy ageing.

Where applicable, experiments conform with Society ethical requirements