Physiology of Voluntary Movement

National Institute Of Neurological Disorders And Stroke

Investigators

Linked publications & trials

Abstract

Several projects in the laboratory were devoted to understanding the physiology of volition. This includes the sense of willing to make a movement and the sense of agency, the sense of personal responsibility for the movement that has occurred. We had been trying to devise improved techniques to get quantitative measures of the timing of these subjective events. We have done studies trying to influence the decision of when or what to move, and to influence the subjective impression of volition, using non-invasive brain stimulation. A major effort in the laboratory seeks to evaluate the causal role of conscious intentions in the willing of movements (NCT04344470). This work is collaborative with an international group of neuroscientists and philosophers. For this purpose, we have been comparing movements triggered by seen and unseen stimuli, producing the unseen stimuli by backward masking. The initial data collection of the first experiment has been completed, and we are exploring the brain events relating to movements made to stimuli that are not appreciated in consciousness. We have studied the timing of the sense of willing in patients with tics, looking at their voluntary movements and their tics. It appears the sense of willing is normally timed, but the brain events are interesting and suggest unconscious mechanisms in play to suppress tic movements. The ability to make selective movements, particularly of individual fingers, is a critical human function. Anatomical and physiological features of the motor system make this difficult since most neurons (other than alpha motoneurons in the spinal cord and brainstem) are not muscle specific. Our hypothesis has been that selective motor action must require inhibitory mechanisms, and we have been seeking to understand them using TMS. We refer to this process as surround inhibition, as muscles not intended for the selective action need to be inhibited. Many inhibitory processes in the cortex, such as short intracortical inhibition and short afferent inhibition, can be analyzed at rest and with movement. We have completed a study using high resolution 7T fMRI to explore patterns of activation in the motor cortex when persons make finger movements. The results were used to evaluate similar activation patterns in patients with focal hand dystonia (NCT03223623). We have also developed a new method of quantifying surround inhibition that is more accurate than our past technique.