Abstract
Repetitive mirror symmetric bilateral upper limb may be a suitable priming technique for upper limb rehabilitation after stroke. Here we demonstrate neurophysiological and behavioural after-effects in healthy participants after priming with 20 minutes of repetitive active-passive bimanual wrist flexion and extension in a mirror symmetric pattern with respect to the body midline (MIR) compared to an control priming condition with alternating flexion-extension (ALT). Transcranial magnetic stimulation (TMS) indicated that corticomotor excitability (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 in ECR and FCR. Short and long-latency intracortical inhibition (SICI, LICI), short afferent inhibition (SAI) and interhemispheric inhibition (IHI) were also examined using pairs of stimuli. 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. We then had participants complete a timed manual dexterity motor learning task with the passive hand during, immediately after, and 24 hours after MIR or control priming. The rate of task completion was faster with MIR priming compared to control conditions. Finally, ECR and FCR MEPs were examined within a pre-movement facilitation paradigm of wrist extension before and after MIR. ECR, but not FCR, MEPs were consistently facilitated before and after MIR, demonstrating no degradation of selective muscle activation. In summary, mirror symmetric active-passive bimanual movement increases CME and can enhance motor learning without degradation of muscle selectivity. These findings rationalise the use of mirror symmetric bimanual movement as a priming modality in post-stroke upper limb rehabilitation.
Highlights
Repetitive transcranial magnetic stimulation offers promise for increasing or decreasing M1 excitability to promote recovery of motor function after stroke [1,2,3,4,5,6,7,8,9], but a practical limitation is that it requires expensive equipment, a medical environment and is contraindicated for people with a history of seizure, metal implants, cardiac pacemaker, or who are taking certain common medications [10,11]
The main finding was a sustained increase in resting passive hemisphere corticomotor excitability after 20 minutes of bimanual active-passive movement made in a mirror symmetric, but not alternating, pattern
This increase in corticomotor excitability (CME) was accompanied in part by pattern-dependent modulation of longlatency intracortical inhibition (LICI), without accompanying changes in short afferent inhibition (SAI) or short latency intracortical inhibition (SICI)
Summary
Repetitive transcranial magnetic stimulation (rTMS) offers promise for increasing or decreasing M1 excitability to promote recovery of motor function after stroke [1,2,3,4,5,6,7,8,9], but a practical limitation is that it requires expensive equipment, a medical environment and is contraindicated for people with a history of seizure, metal implants, cardiac pacemaker, or who are taking certain common medications [10,11]. Motor point stimulation [13,14] and combined peripheral nerve and TMS can enhance or suppress M1 excitability through presumed spike-timing dependent mechanisms [15,16,17] and require expensive equipment, skilled operators, or lengthy treatment periods and has potential contraindications. Enhanced M1 excitability and presumed GABAergic M1 disinhibition have been noted during production of mirror symmetric active-passive bimanual movement [23,24] and may facilitate upper limb recovery after stroke by acting as a neurophysiological priming mechanism [18,19]. There has been no direct examination of M1 excitability and inhibition immediately after repetitive activepassive bimanual movement and no examination of the immediate behavioural consequences of active-passive movement priming
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