Date Presented 4/7/2016
This study informs practice by indicating the degree of neuromodulation attainable with repetitive wrist extension in survivors of stroke. This is important because of recent advancements in using technologies such as transcranial magnetic stimulation to influence neuromodulation and neuroplasticity.
Primary Author and Speaker: Crystal Massie
Contributing Authors: Caylen White, Damian Funke
PURPOSE: The objective of this study was to determine how engaging in isometric motor practice acutely influences motor control, dexterity, and neuromodulation. The hypothesis is that engaging in wrist extension isometric contractions will improve motor control immediately after the practice and may influence cortical excitability.
RATIONALE: Neuroplasticity is an important factor for upper-extremity stroke rehabilitation. Recent trends in stroke rehabilitation research have focused on influencing neuroplasticity with neuromodulatory techniques such as repetitive transcranial magnetic stimulation (rTMS) and coupling those with motor practice. However, the amount of neuromodulation achieved with an acute session of motor practice is not fully characterized.
DESIGN: This was a single-group, pre–post study.
PARTICIPANTS: Five survivors of stroke were recruited from the community to volunteer for this study and were screened for eligibility before providing informed consent. Participants had a mean age of 60.4 (range = 43–84) and had unilateral clinical presentation of a stroke ≥6 mo before the study.
METHOD: Participants completed an assessment immediately before and after motor practice. Assessments included force steadiness and electromyography during a wrist extension task, the Box and Block Test (BBT), and transcranial magnetic stimulation (TMS) before and after the intervention. The force steadiness task was two trials of at least 10 s at 5%, 10%, and 20% of the maximum voluntary contraction. The BBT is a measure of dexterity assessed as the number of small blocks moved in a minute. The TMS measures included 12 stimulations each at suprathreshold test stimulus (TS; 116% of resting motor threshold), short-interval intracortical inhibition (SICI), and intracortical facilitation with motor evoked potentials (MEP) recorded from the extensor carpi radialis and extensor carpi ulnaris muscles.
ANALYSIS: The peak-to-peak amplitude was calculated for each MEP and then averaged. Data were analyzed with a paired t test.
RESULTS: The variability of force steadiness decreased after the intervention for the 5% and 20% conditions (p < .05). Muscle activity increased from pretest to posttest with significant increases during the 10% condition (p = .04) and a trend during the 5% and 20% conditions (ps = .06 and .05, respectively). Participants were able to move significantly more blocks with their stroke-affected hand after the intervention (p < .02), but no changes were observed in the less-affected hand (p = .3). TMS data were collected on only 3 participants. Two participants had increases in MEP amplitude of the TS-only stimulations, and all 3 participants had more inhibition (SICI).
DISCUSSION: These results suggest that a short intervention of isometric wrist extension can influence motor control, dexterity, and neuromodulation. This demonstrates the importance of better understanding how possible rehabilitation interventions contribute to influencing neuroplasticity through neuromodulation.
IMPACT STATEMENT: This study informs practice by indicating the degree of neuromodulation attainable with specific, repetitive practice of isometric wrist extension in survivors of stroke. This is an important consideration in research studies implementing technologies such as repetitive TMS to influence neuromodulation as an adjunct for stroke rehabilitation because it highlights the strength of voluntary practice as a stimulus for neuromodulation.
