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Corticospinal excitability underlying digit force planning for grasping in humans
Pranav Parikh1, Marco Davare2, Patrick McGurrin3
1School of Biological and Health Systems Engineering, Arizona State University, Tempe, Arizona;
Journal of Neurophysiology
|February 7, 2014
Summary
Neural mechanisms for digit force planning were investigated using transcranial magnetic stimulation (TMS). Force planning modulated corticospinal excitability (CSE) before object contact, suggesting external brain area involvement.
Area of Science:
- Neuroscience
- Motor Control
- Human Motor Performance
Background:
- Grasping force control depends on sensorimotor memory and real-time sensory feedback.
- Neural mechanisms for planning digit forces during grasping remain largely uncharacterized.
Purpose of the Study:
- To investigate the neural mechanisms underlying digit force planning during reach-to-grasp tasks.
- To examine the temporal evolution of corticospinal excitability (CSE) and M1 intracortical circuitry during force planning.
Main Methods:
- Utilized single-pulse and paired-pulse transcranial magnetic stimulation (TMS) to assess corticospinal excitability (CSE) and intracortical inhibition/facilitation.
- Compared CSE during low-force (LF) and high-force (HF) reach-to-grasp tasks in 18 participants.
- Measured muscle-specific CSE modulation relative to the reach initiation signal.
Main Results:
- High-force (HF) planning led to significantly reduced CSE compared to low-force (LF) planning, specifically at the time of reach initiation.
- CSE modulation during force planning was specific to the task-relevant muscles.
- No significant modulation of M1 intracortical inhibitory or facilitatory circuits was observed during digit force planning.
Conclusions:
- Digit force planning, reflected by CSE modulation, begins before object contact.
- The findings suggest that force planning relies on neural inputs from frontoparietal areas outside of the primary motor cortex (M1).
