Siobhan Dongés – Abstract

P03      Paired corticospinal-motoneuronal stimulation does not improve maximal voluntary elbow flexion in people with incomplete cervical spinal cord injury

Dongés SC[1], Boswell-Ruys CL[1], Butler JE[1,2] and Taylor JL[1,2,3]

  1. NeuRA, Sydney, Australia
  2. University of New South Wales, Sydney, Australia
  3. Edith Cowan University, Perth, Australia

Corticospinal transmission to motoneurones can be modified using repeated pairs of stimuli to presynaptic corticospinal neurones and postsynaptic motoneurones. This technique, termed paired corticospinal-motoneuronal stimulation (PCMS), can modify evoked muscle potentials and voluntary motor performance in people with and without spinal cord injury (1-4). Maximal voluntary performance after PCMS has only been assessed for thumb adduction in people without spinal cord injury (3). Here, we hypothesised that PCMS would enhance maximal voluntary elbow flexion in people with incomplete cervical spinal cord injury. PCMS comprised 100 stimulus pairs (transcranial magnetic and electrical peripheral nerve stimulation) at 0.1 Hz, timed so corticospinal potentials arrived at corticospinal-motoneuronal synapses 1.5 ms before antidromic motoneuronal potentials. On two days (5-22 days apart), sets of 5 maximal elbow flexions were performed by 11 individuals with spinal cord injury (C4/C5 level) before and after PCMS or control (100 peripheral nerve stimuli) conditioning. To measure maximal voluntary activation, supramaximal biceps brachii stimulation elicited superimposed twitches during contractions, which were normalised to resting twitches. Torque and electromyographic activity during contractions were also assessed. Baseline median (interquartile range) maximal torque was 11 Nm (10 to 25 Nm) and voluntary activation was 92% (83 to 96%). There were no significant differences in outcome measures between PCMS and control protocols after conditioning. Thus, PCMS did not improve maximal motor output for this group. Possible explanations for the lack of effect include a potential ceiling effect for voluntary activation, or that PCMS may be less effective for elbow flexors than more distal muscles.

  1. Taylor JL & Martin PG (2009) J Neurosci 29, 11708-11716
  2. Bunday KL & Perez MA (2012) Curr Biol 22, 2355-2361
  3. D’Amico JM, Dongés SC & Taylor JL (2018) J Neurophysiol 119, 369-376
  4. Dongés SC, D’Amico JM, Butler JE & Taylor JL (2018) J Neurophysiol 119, 652-661