Neural correlates of task-related changes in physiological tremor

Abstract

Laine CM, Negro F, Farina D. Neural correlates of task-related changes in physiological tremor. J Neurophysiol 110: 170 -176, 2013. First published April 17, 2013 doi:10.1152/jn.00041.2013.-Appropriate control of muscle contraction requires integration of command signals with sensory feedback. Sensorimotor integration is often studied under conditions in which muscle force is controlled with visual feedback. While it is known that alteration of visual feedback can influence task performance, the underlying changes in neural drive to the muscles are not well understood. In this study, we characterize the frequency content of force fluctuations and neural drive when production of muscle force is target guided versus self guided. In the self-guided condition, subjects performed isometric contractions of the first dorsal interosseous (FDI) muscle while slowly and randomly varying their force level. Subjects received visual feedback of their own force in order to keep contractions between 6% and 10% of maximum voluntary contraction (MVC). In the targetguided condition, subjects used a display of their previously generated force as a target to track over time. During target tracking, force tremor increased significantly in the 3-5 and 7-9 Hz ranges, compared with self-guided contractions. The underlying changes in neural drive were assessed by coherence analysis of FDI motor unit activity. During target-guided force production, pairs of simultaneously recorded motor units showed less coherent activity in the 3-5 Hz frequency range but greater coherence in the 7-9 Hz range than in the self-guided contractions. These results show that the frequency content of common synaptic input to motoneurons is altered when force production is visually guided. We propose that a change in stretchreflex gain could provide a potential mechanism for the observed changes in force tremor and motor unit coherence.

Jaw tremor as a physiological biomarker of bruxism

“…It is worth pointing out that when the magnitude or gain of afferent feedback is increased during a force tracking task, a relatively consistent pattern of effects emerges (higher 8 Hz tremor, lower 1-3 Hz common input, higher 8 and 20-40 Hz common input) (Laine et al, 2013(Laine et al, , 2014. For example, this pattern emerged in the study of Laine et al (2014) after the gain of afferent feedback was increased through manipulation of visual task parameters.…”

Effects of transcranial direct current stimulation in combination with motor practice on dexterous grasping and manipulation in healthy older adults

“…The descending motor commands, along with other inputs from muscle spindles and tendon organs onto the alpha-motor neurons, could modulate the variability of grip force (Enoka et al 2003;Tracy et al 2007). Furthermore, the burden of visuomotor processing (e.g., during our vision condition) increases oscillations in the descending drive, and/or alters the frequency content of common synaptic inputs to the active motor units leading to increased force fluctuations during the production of steady voluntary forces under conditions of visual force feedback (Tracy et al 2007;Laine et al 2013).…”

Task‐related changes in sensorimotor integration influence the common synaptic input to motor neurones

“…Additionally, we predicted that a more demanding visual task would increase force tremor and motor unit coherence in the 6–12 Hz range (Laine et al . ), as would be expected from increased action in the spinal stretch‐reflex loop (Erimaki & Christakos , , Christakos et al . ).…”