Department of Exercise Sciences


Mirror symmetric bimanual movement priming can increase corticomotor excitability and enhance motor learning

Winston D. Byblow, Cathy M. Stinear, Marie-Claire Smith, Lotte Bjerre, Brain K. Flaskager, Alana B. McCambridge
Published in PLoS ONE (2012); 7 (3): e33882

Introduction

Repetitive mirror symmetric bilateral upper limb movement may be a suitable priming technique for upper limb rehabilitation after stroke. Until now, there has been no direct examination of M1 excitability and inhibition immediately after repetitive active-passive bimanual movement and no examination of the immediate behavioural consequences.

 

Aim

To demonstrate neurophysiological and behavioural after-effects after repetitive mirror symmetric wrist flexion-extension movements (MIR) compared to a control condition with alternating flexion-extension (ALT).

 

Method

  • Table 1 summarises the design of each experiment (Exp) (Table 1). Right-handed participants were neurologically healthy and with no upper limb injuries.
  • Exp 1-3 required two sessions, one for each active-passive movement pattern (MIR, ALT), but were otherwise identical. Data were collected at four times: before movement (Pre/Baseline), immediately (Post0), 15 and 30 minutes after movement (Post15 and Post30).
    • In Exp 1, CME, short-latency afferent inhibition (SAI) and long-interval intracortical inhibition (LICI) were investigated using single and paired-pulse TMS targeting right extensor carpi radialis (ECR) and flexor carpi radialis (FCR) representations in left M1.
    • In Exp 2, interhemispheric inhibition (IHI) from right to left M1 was examined using dual-coil TMS targeting both left and right FCR.
    • In Exp 3, right FCR H-reflexes were examined.
  • In Exp 4, the effect of bilateral priming on motor skill learning was examined using a timed grooved pegboard test (GPT). Participants were randomised into 3 groups, performing either MIR, ALT or no (NONE) movement priming, and the nondominant (left) hand was passive during MIR and ALT. An initial measure was taken as baseline, followed by four attempts during, immediately after, and 24 h after active-passive movement priming or no movement priming. The time between attempts was 5 min.
  • In Exp 5, participants completed one session of MIR active-passive movement. CME and short latency intracortical inhibition (SICI) were investigated before and after MIR using single and paired-pulse TMS, targeting right ECR and FCR representations in left M1. Pre-movement facilitation (PMF) was examined before and after MIR using single pulse TMS delivered within the reaction time (RT) interval of right wrist extension. Data were collected at 3 time points: baseline, immediately after APBT (Post0) and 30 minutes after APBT (Post30).

 

Results

  • Exp 1-3: Transcranial magnetic stimulation (TMS) indicated that CME of the passive hemisphere remained elevated compared to baseline for at least 30 minutes after MIR but not ALT, evidenced by an increase in the size of motor evoked potentials (MEPs) in ECR and FCR. LICI differed between patterns, with less LICI after MIR compared with ALT, and an effect of pattern on IHI, with reduced IHI in passive FCR 15 minutes after MIR compared with ALT and baseline. There was no effect of pattern on SAI or FCR H-reflex. Similarly, SICI remained unchanged after 20 minutes of MIR.
  • Exp 4: The rate of task completion was faster with MIR priming compared to control conditions (ALT and NONE).
  • Exp 5: MIR facilitated M1 excitability for at least 30 minutes, but it had no effect on SICI in either ECR or FCR. ECR, but not FCR, MEPs were consistently facilitated before and after MIR, demonstrating no degradation of selective muscle activation.
Byblow-2012-Table-1

Interpretation

 

The present results indicate that in healthy participants, CME is increased for at least 30 minutes after mirror symmetric, but not alternating movement patterns. The enhanced CME is similar in extent and duration to that obtained after noninvasive M1 stimulation and may be medicated, at least in part, via modulation of interhemispheric inhibition. Furthermore, mirror symmetric movement accelerated motor learning without degrading selective muscle activation. This strengthens the assertion that mirror symmetric active-passive movement may be an effective priming modality for enhancing use-dependent plasticity within primary motor cortex.

 

In a practical view, two thirds of patients who experience stroke are left with lingering upper limb impairment with little option for recovery of function. The present results indicate that a single 20 minute session of MIR may induce persistent increases in CME in the stroke hemisphere, which carry over into the motor training period. These results lend support to the potential utility of active-passive bilateral priming as a therapeutic adjuvant for upper limb recovery after stroke.

 

Acknowledgements

We thank Madeline Barbarich, Andrew McIntyre-Robinson, Allan Plant, Fred Noten and Phil Lacey for assistance with data collection, analysis, and technical support.