Hemispheric differences in motor cortex excitability during a simple index finger abduction task in humans

Area of Science:

• Neuroscience
• Motor Control
• Human Physiology

Background:

• The corticospinal pathway is crucial for voluntary movement.
• Understanding its role in hand muscle activation is key to motor control research.
• Individual differences in corticospinal excitability may exist between hands.

Purpose of the Study:

• To compare corticospinal pathway involvement in index finger abduction between dominant and nondominant hands.
• To investigate the influence of contraction force on corticospinal excitability.
• To differentiate corticospinal contributions from spinal contributions.

Main Methods:

• Used transcranial magnetic stimulation (TMS) and transcranial electrical stimulation (TES) on 16 right-handed subjects.
• Measured motor-evoked potentials (MEPs) in the first dorsal interosseous (FDI) muscle during isometric index finger abduction at various force levels.
• Compared MEP facilitation during contraction between hands and between stimulation types.

Main Results:

• Contraction-induced MEP facilitation in FDI was significantly greater for the nondominant hand compared to the dominant hand with TMS.
• This difference was more pronounced at lower contraction forces.
• TES showed similar MEP facilitation for both hands, indicating equivalent spinal excitability.

Conclusions:

• Corticospinal neuron involvement in index finger abduction is generally greater for the nondominant hand in right-handed individuals.
• This suggests a more significant role of the corticospinal pathway in controlling the nondominant hand for this task.
• Findings highlight potential lateral differences in motor control strategies.