Stopping speech suppresses the task-irrelevant hand

Abstract

Some situations require one to quickly stop an initiated response. Recent evidence suggests that rapid stopping engages a mechanism that has diffuse effects on the motor system. For example, stopping the hand dampens the excitability of the task-irrelevant leg. However, it is unclear whether this 'global suppression' could apply across wider motor modalities. Here we tested whether stopping speech leads to suppression of the task-irrelevant hand. We used Transcranial Magnetic Stimulation over the primary motor cortex with concurrent electromyography from the hand. We found that when speech was successfully stopped the motor evoked potential from the task-irrelevant hand was significantly reduced compared to when the participant failed to stop speaking, or responded on non stop signal trials, or compared to baseline. This shows that when speech is quickly stopped, there is a broad suppression across the motor system. This has implications for the neural basis of speech control and stuttering.

Figure 1

a. A vocal version of the stop-signal task: participants named a letter “T” or “D” (a go signal) on each trial; on 33% of trials, the letter turned red (a stop signal) and participants tried to cancel the vocal response. TMS stimulation was given at 100 ms before average RT on TMS trials. b. Examples of the sound wave for the Go, StopSucc and StopFail trials with TMS stimulation. Note that TMS stimulation induced a sharp but weak audio signal around 400 ms whereas the human sound wave had a large amplitude and long duration. c. A figure-of-eight coil was placed over the left primary motor cortex and EMG was recorded from the right hand. d. MEP on the StopSucc trials was significantly smaller than on the Go, StopFail and baseline TMS trials (all ps < 0.05).