Operant Conditioning of the Motor Evoked Potential in Forearm Extensors of Individuals with Chronic Incomplete Cervical Spinal Cord Injury: Case Studies.

Abstract

Background: Operant up-conditioning of the motor evoked potential (MEP) elicited by transcranial magnetic stimulation can increase corticospinal excitability for the ankle dorsiflexor and improve its activation in individuals with foot drop due to chronic incomplete spinal cord injury (SCI). It is unknown whether MEP up-conditioning can work similarly in the upper limb (UL).

Objectives: As the first step in testing the possibility of MEP up-conditioning enhancing UL neurorehabilitation, we examined the effects of forearm extensor MEP up-conditioning in 6 adults with chronic incomplete cervical SCI.

Methods: In a research laboratory setting, each participant completed 6 baseline and 24 MEP up-conditioning sessions, during which wrist or finger extensor MEPs were elicited with or without feedback on MEP size. MEP size, silent period (SP) duration, and EMG activity during maximum voluntary contraction (MVC) were measured in each session. Before and after 24 conditioning sessions, Action Research Arm Test (ARAT), Box and Block Test (BBT), and Spinal Cord Independence Measure III (SCIM III) were administered.

Results: Over the course of study, MVC increased in all participants by 26% to 329%. MEP size increased in 4 participants by 95% to 204%. SP duration decreased in 4 participants by 22% to 38%. Functional scores increased by 2 to 7 points for SCIM III self-care score in 5 participants, by 1 to 10 points for ARAT in 4 participants, and by 4 to 6 blocks for BBT in 4 participants.

Conclusion: These cases support that MEP up-conditioning can improve corticospinal drive and activation of forearm muscles and improve UL motor function in individuals with chronic incomplete cervical SCI.