Speed of processing in the primary motor cortex: a continuous theta burst stimulation study

Area of Science:

• Neuroscience
• Motor Control
• Human Physiology

Background:

• Temporally urgent reactions involve rapid movements triggered by stimuli.
• The role of the primary motor cortex (M1) and stimulus intensity in these reactions is unclear.
• Continuous theta burst stimulation (cTBS) can modulate M1 activity to study processing speed.

Purpose of the Study:

• To investigate M1 involvement in processing speed relative to stimulus intensity.
• To assess the effects of cTBS on motor cortical excitability and reaction time.

Main Methods:

• Thirteen healthy adults underwent median nerve stimulation (high/low intensity) and simple button presses.
• Reaction time was measured via electromyography of the first dorsal interosseous (FDI) muscle.
• cTBS was applied to the right FDI's motor cortical representation, with motor evoked potentials (MEPs) recorded before and after.

Main Results:

• cTBS induced variable effects on MEP amplitude: 5 attenuated, 3 facilitated, 5 unchanged.
• A subset with attenuated MEPs showed an interaction between stimulus intensity and cTBS effect on reaction time and muscle activation.
• High stimulus intensity and motor cortical excitability changes correlated with processing speed.

Conclusions:

• The effects of cTBS on motor cortex excitability are variable.
• Motor cortical excitability changes may significantly influence processing speed, particularly with high-intensity stimuli.
• Further research into cTBS mechanisms is needed.