On the neural expression of task-stabilizing synergies across motor units of single muscles
Open Access
- Author:
- Ricotta, Joseph
- Graduate Program:
- Kinesiology (PHD)
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- June 02, 2023
- Committee Members:
- Jonathan Bates Dingwell, Professor in Charge/Director of Graduate Studies
Robert Sainburg, Major Field Member
Xuemei Huang, Co-Chair & Dissertation Advisor
Patrick Drew, Outside Unit & Field Member
Tarkeshwar Singh, Major Field Member
Mark Latash, Co-Chair & Dissertation Advisor - Keywords:
- Motor control
Motor neuroscience
Spinal cord
Parkinsons
Fatigue
Stability
Synergy - Abstract:
- Given any single motor task, the central nervous system generally faces an infinite number of possible solutions. How the nervous system reliably arrives at any given motor solution has been a topic of scientific and clinical concern since the time of N.A. Bernstein. One mechanism is synergic control, here defined in two parts as (i.) the grouping-together of multiple motor elements and (ii.) the coordination of these groups to satisfy a given task. This dissertation explores the behavioral mechanisms behind task-stabilizing synergies at the level of single neuron/muscle fiber pairs, termed motor units (MU), measured using surface electromyography in humans. It has been previously established that MUs form groups (MU-modes) in single muscles and coordinate together to stabilize force production within these muscles. Here, evidence is advanced suggesting that these MU-groups are found throughout the body and demonstrate some expected responses to perturbations involving disinhibition of the alpha-motoneuronal pool. Specifically, this dissertation advances findings that (i.) MU-modes are not simply artifacts of muscle compartmentalization in arm muscles, and (ii.) paradigms of altered alpha-motoneuron disinhibition predictably alter force-stabilizing synergies formed by MU-modes. These paradigms include fatiguing exercise and Parkinson’s disease. In the latter population, metrics of stability demonstrate diagnostic promise. It is hypothesized that MU-mode synergies are not fully explained by descending excitatory influences and are likely to emerge from a non-uniform inhibitory architecture across motoneurons in the spinal cord. Such an architecture may exert selection pressures favoring task-concordant patterns of excitation over those destabilizing task performance.