Anticipatory corticospinal control of movements in healthy subjects and in patients with neurological motor deficits
Final Report Abstract
Anticipation is an important feature of motor behavior allowing the nervous system to prevent undesirable consequences of external or internal perturbations to minimize movement errors and maintain balance. Anticipation involves several brain areas, the activity of which often begins to increase long before the onset of motor actions. In this project, the role of corticospinal (CS) pathways in anticipatory motor actions was evaluated using transcranial magnetic stimulation (TMS) of the primary motor cortex projecting to motoneurons (MNs) of wrist muscles. Preloaded wrist flexors were suddenly unloaded by the experimenter or by the subject using the other hand (self-unloading). After sudden unloading, the wrist joint involuntarily flexed to a new position. In contrast, during self-unloading the wrist remained almost motionless, implying that an anticipatory postural adjustment occurred. In the self-unloading task, anticipation was manifested by a decrease in descending facilitation of pre-activated flexor MNs before changes in the background electromyographic (EMG) activity. Descending facilitation of extensor MNs began to increase later. Conversely, these influences remained unchanged before sudden unloading, implying the absence of anticipation. TMS responses were also tested during EMG silent periods produced by brief muscle shortening, transiently resulting in similar EMG levels before the onset and after the end of self-unloading. Descending facilitation of flexor MNs was reduced after self-unloading. To explain why the wrist excursion was minimized in self-unloading due to these changes in descending influences, results were interpreted based on previous demonstrations that descending systems pre-set the threshold positions of body segments at which muscles begin to be activated, thus predetermining the equilibrium point to which the system is attracted. Based on this notion, a more consistent explanation of the kinematic, EMG and descending patterns in the two types of unloading is proposed compared to the alternative notion of direct pre-programming of kinematic and/or EMG patterns. The study advances the understanding of how motor actions in general, and anticipation in particular, are controlled.
Publications
- (2016), “Anticipatory corticospinal control of motoneurons during self-unloading of wrist muscles: Comparison with usual unloading”. Society for Neuroscience, San Diego, USA (Abstract)
L. Zhang, A. Feldman
- (2017). Referent control of body orientation in the gravitational field: the role of the vestibulospinal system. Progress in Motor Control, Miami, USA (Abstract)
L. Zhang, A. Mullick, J. Davot, M. Levin MF, A. Feldman
- “Threshold Position Control of Anticipation in Humans: A Possible Role of Corticospinal Influences”. Journal of Physiology (London), 2017
L. Zhang, N. Turpin, A. Feldman
(See online at https://doi.org/10.1113/JP274309)
