Developing a New Protocol for the Inhibition of Long-Latency Stretch Reflexes Using TMS and a Wrist Robot

• Gabriella Rodriguez, Biomedical Engineering, University of Delaware

• Fabrizio Sergi, Biomedical and Mechanical Engineering, University of Delaware

Multiple motor pathways contribute to wrist motor function. Inhibition of the corticospinal tract, the primary motor pathway, would allow for studying the causal role of secondary motor pathways on wrist motor function. Transcranial Magnetic Stimulation (TMS) is a non-invasive brain stimulation technique capable of decoupling the contribution of motor pathways during wrist movements. However, the precise TMS intensity and timing that maximally reduce the stretch reflex response at the wrist are unknown. Additionally, due to the technical complexities of TMS protocols, it is crucial to have detailed protocol documentation for repeatability and quality assurance. The objective of this work is to develop and record a protocol that combines TMS with wrist perturbations and either MRI or electromyography to determine the effect of TMS on stretch reflexes. In these experiments, three levels of TMS were applied (no TMS, subthreshold TMS, or suprathreshold TMS) at various latencies prior to a wrist perturbation to determine the effect of TMS intensity and timing on the stretch reflex response. In the MRI scanner, the same TMS conditions are applied to quantify the effect of TMS on the neural function associated with a stretch reflex. Both experiments require determining the participant’s active motor threshold (AMT) prior to the experiment. The experimental setup and procedures were documented in the protocol. Since these setups are technically involved, schematics of the setup are made to visually represent the connections of both experiments. In addition to the schematics, images of the equipment, written descriptions of the equipment, a table of MRI-safe equipment, and instructions on the experimental procedure are included in the document. This documentation will allow other researchers to recreate the experiment. Additionally, information found in the document can be used to report in scientific publications. The outcomes of these experiments will further our understanding of how TMS modulates corticospinal output and the roles of secondary motor pathways on wrist function.