Neurophysiology of movement inhibition during full body reaching

Abstract

Our current understanding of response inhibition comes from go/no-go studies that draw conclusions based on the overt movement of single limbs (i.e., a single finger pushing a button). In general, go/no-go paradigms have found that an individual's ability to correctly inhibit the motor system is indicative of a healthy central nervous system. However, measuring inhibition by an overt behavioral response may lack the sensitivity to conclude whether the motor system is completely inhibited. Therefore, our goal was to use behavioral and neurophysiological measures to investigate inhibition of the motor system during a full-body reaching task. When directly comparing neurophysiological and behavioral measures, we found that neurophysiological measures were associated with a greater number of errors during no-go trials and faster onset times during go trials. Further analyses revealed a negative correlation between errors and onset times, such that the muscles that activated the earliest during go trials also had the greatest number of errors during no-go trials. Together, our observations show that the absence of an overt behavioral response does not always translate to total inhibition of the motor system.

Figure 1

Results from errors of commission analysis across no-go trials and onset analysis across go trials. (A,B) show the results of the errors of commission analysis during no-go trials. In general, (A) demonstrates that hand position had significantly less errors than all the muscles we investigated. (B) shows the mean difference for errors of commission between muscles and hand position. Color demonstrates level of significance with grey indicating a p-value > 0.05, and dark pink indicating a p-value < 0.01. (C,D) show the results of the onset analysis across go trials. In general, (C) shows that onset time was significantly slower for hand position than all the muscles we investigated, except the left multifidus. (D) shows the mean difference for onset between muscles and hand position. RT right tibialis, LT left tibialis, RM right multifidus, LM left multifidus, D right deltoid, HP hand position.

Figure 2

Relationship between errors of commission and onset. Each symbol on the scatter plot is indicative of an individual’s mean error of commission and mean onset. The overall trend of the scatter plots shows a negative correlation with higher errors of commission during no-go trials being associated with faster onsets during go trials.

Figure 3

Individual trial of virtual reality-reaching task. Each square shows the visual display that the participant viewed in the VR environment. Cartoon figures reflect an example of subject posture during each phase of the trial. Participants started each trial with upright posture with both hands hanging at their side. After 8500 ms of rest, a blue cube appeared and represented the target they would reach out and touch. After 2000 ms, the same cube turned green or red. Participants were instructed to reach to the target if it turned green or stand still if it turned red. The red/green target remained on the screen for 750 ms. The blue, green and red bars under each square correspond with the blue, green, and red target cube. These bars were not visible to the participant.

Figure 4

EMG threshold detection. Example EMG activity (black line) is shown during a go trial (a), a no-go trial with no error of commission (b), and a no-go trial with a error of commission (c). The correct response to a no-go trial was to stand completely still when the red cube appeared. An error during a no-go trial was the production of muscle activity in response to the appearance of the red cube. The blue, green, and red bars represent the appearance of the blue, green, and red cube. The grey shading represents the threshold. Trial “b” is labelled as correct because the peak amplitude does not cross the threshold, while trial “c” is labelled as an error because the peak amplitude crosses the threshold.