Primary motor cortex function and motor skill acquisition: insights from threshold-hunting TMS

Area of Science:

• Neuroscience
• Motor Control
• Neuroplasticity

Background:

• Modulation of GABA-mediated inhibition in the primary motor cortex (M1) is crucial for motor learning and skill acquisition.
• Short-interval intracortical inhibition (SICI), a measure of GABA-related inhibition, is typically assessed using paired-pulse transcranial magnetic stimulation (TMS).
• Previous studies show inconsistent modulation of SICI with motor skill learning, potentially due to variations in TMS parameters.

Purpose of the Study:

• To compare the modulation of SICI during motor skill learning using conventional versus adaptive threshold-hunting TMS techniques.
• To investigate the effect of anterior-posterior (AP) versus posterior-anterior (PA) induced current on SICI modulation.
• To determine the optimal TMS approach for assessing changes in motor cortex inhibition during skill acquisition.

Main Methods:

• Sixteen participants trained a sequential visual isometric pinch task with their dominant hand.
• Electromyography (EMG) recorded from the first dorsal interosseous muscle.
• Corticomotor excitability and SICI were measured before and after training using conventional and adaptive threshold-hunting TMS with AP and PA currents.

Main Results:

• Motor skill improved throughout training, with performance plateauing before completion.
• Corticomotor excitability increased post-training for both AP and PA currents.
• SICI was greater with AP stimulation compared to PA, irrespective of the technique.
• SICI significantly increased after motor training specifically with adaptive threshold-hunting using an AP-induced current.

Conclusions:

• Increased GABA-mediated inhibition following motor skill learning, as detected by adaptive threshold-hunting TMS with AP current, may facilitate skill consolidation.
• Adaptive threshold-hunting SICI with an AP-induced current is a sensitive method for assessing changes in motor cortex inhibition during motor learning.
• This approach holds promise for interventional studies investigating motor plasticity.