Functional Implications of Motor Evoked Potential Operant Conditioning of Wrist Extensors in an Individual Poststroke

PURPOSE: Each year ∼795,000 people have a new or recurrent stroke (Virani et al, 2018), and about 50% of those individuals will have lasting upper extremity (UE) impairment (Broeks, et al, 1999). This impairment negatively impacts the individual’s ability to participate in meaningful activities and can increase caregiver burden. Many individuals have weak wrist extension, making grip, grasp, and functional hand positioning challenging. Recent studies have shown that people with or without incomplete SCI can increase the size of the ankle dorsiflexor motor evoked potential (MEP) through operant up-conditioning (Thompson, et al, 2018), and that it improves gait in people with SCI (Thompson, et al, 2019). In addition, preliminary data suggests that MEP operant conditioning can increase wrist extensor activity in individuals with chronic SCI. Building on those studies, this study proposes to test an MEP operant conditioning protocol for enhancing upper extremity function in chronic stroke. To enhance upper extremity rehabilitation beyond what conventional therapy can do alone, we are testing the hypothesis that extensor carpi radialis (ECR) MEP operant up-conditioning will increase wrist extensor activity and upper extremity function in individuals with chronic stroke.

DESIGN: This is a case study of a 56-year-old female who was 2.5 years post-ischemic subcortical stroke with moderate-mild UE impairment (FMA-UE score 40).

METHOD: The participant was exposed to 6 baseline and 24 MEP up-conditioning sessions (3 sessions/wk over 10 wks). In all sessions, ECR MEPs were elicited at 10% above motor threshold while the participant maintained a pre-set absolute amplitude of background EMG activity (equivalent to baseline ∼30% maximum voluntary contraction (MVC) level). In all 225 MEP trials of baseline sessions and control sessions and the first 20 trials of each conditioning session, the participant received no feedback as to MEP size (i.e., control MEPs). Then, in 225 conditioning trials of each conditioning session, the participant was asked to increase MEP size, and received immediate feedback as to whether MEP was larger than a criterion (i.e., whether the trial was a success). The Fugl-Meyer Upper Extremity Assessment (FMA-UE), Action Research Arm Test (ARAT), and Box and Block Test (BBT) were administered at baseline, after 12 conditioning sessions, after 24 conditioning sessions (post-training), and 6 weeks after completing the training.

RESULTS: The participant’s ECR MVC increased to 200% of baseline value over the course of 24 conditioning sessions. Furthermore, we observed an 8-point increase in FMA-UE score, and an increase from 11 boxes moved to 17 boxes moved on BBT from baseline to immediately after 24 conditioning sessions. These gains were retained up to 6 weeks post-training. There was no change in ARAT score.

CONCLUSION: The results support our hypothesis that operant conditioning of ECR MEP can increase voluntary activation of wrist extensors and improve upper extremity function in an individual with chronic stroke. These improvements were maintained post-training up to 6 weeks, and the participant began using her affected dominant hand to write again, demonstrating a clear functional impact. Given these results, we believe it’s possible that operant conditioning implemented as an adjunct to traditional occupational therapy could enhance functional outcomes beyond what is currently possible. We plan to enroll additional participants to continue to explore the effects of MEP operant conditioning on UE function. We also plan to explore how to best pair operant conditioning with traditional therapy to achieve the maximum benefit (i.e. concurrent vs. sequential, identifying appropriate protocols, etc.)

References

Virani, SS, et al. (2020). Heart Disease and Stroke Statistics—2020 Update: A Report from the American Heart Association. Circulation. 141:e139-e596. https://doi.org/10.1161/CIR.0000000000000757

Broeks, JG, Lankhorst, GJ, Rumping, K, & Prevo, JH. (1999). The long-term outcome of arm function after stroke: results of a follow-up study, Disability and Rehabilitation, 21:8, 357-364. https://doi.org/10.1080/096382899297459

Thompson AK, Cote RH, Sniffen JM, Brangaccio JA. (2018). J Neurophysiol. 120:2745-2760. https://doi.org/10.1152/jn.00362.2018

Thompson AK, Fiorenza G, Smyth L, Favale B, Brangaccio J, Sniffen J. (2019). J Neurophysiol. 121(3):853-866. https://doi.org/10.1152/jn.00557.2018