Electromyography Markers of Global Motor Inhibition While Stopping

Presenter: Isaiah Mills – Human Physiology

Faculty Mentor(s): Ian Greenhouse, Mitchell Fisher

Session: (In-Person) Poster Presentation

Stopping individual parts of complex movement plans is a critical part of controlling our bodies. While humans can coordinate movements effectively, our brains have limitations in selective stopping ability. Cancelling one action can affect other simultaneous actions, especially when these actions are bimanual. In one stopping task where participants had to cancel one finger movement while continuing a movement with the other hand, the executed lift was delayed from the target reaction time. This is thought to be caused by a neural pathway which nonselectively inhibits all actions before restarting continuing actions. Here, we record the activation of little finger muscles using electromyography during tonic muscle contraction. Subjects hold contraction as they perform a similar task involving timing bimanual index finger movements to a target time. During stop trials where one or both movements are inhibited we hypothesize that the amplitude of tonic EMG will decrease representing nonselective motor inhibition. Preliminary data analysis supports this hypothesis. This data will help us understand how healthy control of movement is facilitated by the brain, and during what period following a stop signal this network is actively suppressing movement. Patients who suffer from movement disorders like Parkinson’s struggle to control inhibitory processes, and we hope to learn more about the disease and how it affects these pathways by comparing healthy datasets to disease state.

The Likelihood of Eliciting Motor Evoked Potentials with Paired Pulse TMS

Presenter(s): Ethan Kizziar

Faculty Mentor(s): Ian Greenhouse

Poster 48

Session: Sciences

The excitability of the corticospinal pathway changes in a dynamic manner. Here, we used paired-pulse transcranial magnetic stimulation (ppTMS) to test the hypothesis that rapid changes within motor cortex determine the likelihood the corticospinal pathway will become active. In six participants, pairs of electromagnetic pulses separated by 3ms were administered over primary motor cortex to induce a twitch, or motor evoked potential (MEP), in a target finger muscle. The first ‘conditioning’ pulse was changed dynamically to a percentage of a subject’s active motor threshold (AMT, the minimum TMS intensity to consistently elicit MEPs during a mild tonic contraction). The second ‘test’ pulse, produced the MEP. Using electromyography to record muscle electrical activity, we calculated MEP sizes of the course of 100 measurements, with 20 measurements at each 5 conditioning pulse intensities.

We observed a recurring pattern of an increased likelihood of eliciting an MEP at higher conditioning pulses. Conditioning pulses at 95% of the subject’s AMT produced MEPs 85% of the time, whereas at 50% AMT, MEPs were only detected on less than 40% of attempts. This finding suggests that momentary increases of excitability within motor cortex determine the likelihood of activating the corticospinal pathway and helps shed light on the mechanisms by which motor cortex mediates corticospinal output to muscles.