Effects of posture and coactivation on corticomotor excitability of ankle muscles

• Type of Material: Article
• Authors: Trisha M. Kesar, Emory University; Steven Eicholtz, Emory University; Bethany J. Lin, Atlanta Veterans Affairs; Steven L Wolf, Emory University; Michael R. Borich, Emory University
• Language: English
• Date: 2018-02-08
• Publisher: IOS Press
• Publication Version: Author Accepted Manuscript (After Peer Review)
• Copyright Statement: ©2018 IOS Press All rights reserved.
• Final Published Version (URL): http://dx.doi.org/10.3233/RNN-170773
• Title of Journal or Parent Work: Restorative Neurology and Neuroscience
• ISSN: 0922-6028
• Volume: 36
• Issue: 1
• Start Page: 131
• End Page: 146
• Grant/Funding Information: TMK is supported by the National Institute of Child Health and Human Development grant number K01 HD079584.; SLW is supported by grants U10NS086607 and U01 NS091951; MRB is supported by the National Institute of Child Health and Human Development grant number K12HD055931 and National Institutes of Health grant number 5R24HD050821-11.
• Keywords: Activation; MOTOR-EVOKED-POTENTIALS; Neurosciences; Neurosciences & Neurology; coactivation; posture; Life Sciences & Biomedicine; motor evoked potentials; REHABILITATION; TMS; ANTAGONISTIC MUSCLES; COCONTRACTION; SOLEUS MUSCLE; neuroplasticity; CORTEX; lower limb; STROKE; FACILITATION; Science & Technology; TRANSCRANIAL MAGNETIC STIMULATION
• Research Categories: Health Sciences, Rehabilitation and Therapy; Biology, Neuroscience

Abstract

BACKGROUND: The use of transcranial magnetic stimulation (TMS) to evaluate corticomotor excitability of lower limb (LL) muscles can provide insights about neuroplasticity mechanisms underlying LL rehabilitation. However, to date, a majority of TMS studies have focused on upper limb muscles. Posture-related activation is an important under-investigated factor influencing corticomotor excitability of LL muscles. OBJECTIVE: The purpose of this study was to evaluate effects of posture and background activation on corticomotor excitability of ankle muscles. METHODS: Fourteen young neurologically-unimpaired participants (26.1±4.1 years) completed the study. TMS-evoked motor evoked potentials (MEPs) were recorded from the tibialis anterior (TA) and soleus during 4 conditions - standing, standing coactivation, sitting, and sitting coactivation. TA and soleus MEP amplitudes were compared during: (1) standing versus sitting;(2) standing coactivation (standing while activating both TA and soleus) versus sitting coactivation; and (3) standing coactivation versus standing. For each comparison, background EMG for TA and soleus were matched. Trial-to-trial coefficient of variation of MEP amplitude and coil-positioning errors were additional dependent variables. RESULTS: No differences were observed in TA or soleus MEP amplitudes during standing versus sitting. Compared to sitting coactivation, larger MEPs were observed during standing coactivation for soleus but not TA. Compared to standing, the standing coactivation task demonstrated larger MEPs and reduced trial-to-trial MEP variability. CONCLUSION: Our findings suggest that incorporation of measurements in standing in future TMS studies may provide novel insights into neural circuits controlling LL muscles. Standing and standing coactivation tasks may be beneficial for obtaining functionally-relevant neuroplasticity assessments of LL musculature.