Corticospinal excitability is enhanced while preparing for complex movements.

Area of Science:

• Neuroscience
• Motor Control
• Human Movement Science

Background:

• Movement complexity is known to increase reaction time (RT).
• Transcranial magnetic stimulation (TMS) reveals movement complexity alters corticospinal excitability.
• The effect of sequential movement components on corticospinal excitability during RT task preparation is not well understood.

Purpose of the Study:

• To investigate how motor evoked potentials (MEPs) in the premotor period are affected by movement complexity within a simple RT paradigm.
• To examine the relationship between movement complexity and corticospinal excitability during the preparatory phase of a simple RT task.

Main Methods:

• Participants (n=12) performed ballistic arm movements to one, two, or three targets.
• Transcranial magnetic stimulation (TMS) was applied during the premotor period at varying percentages of reaction time (RT).
• Motor evoked potentials (MEPs) were recorded from the triceps brachii muscle.

Main Results:

• Premotor reaction time (RT) increased with task complexity.
• Background electromyographic activity (EMG) in the triceps brachii remained consistent across conditions.
• MEP amplitude significantly increased with movement complexity at 80% of premotor RT.

Conclusions:

• Increased corticospinal excitability, indicated by larger MEPs, accompanies greater movement complexity prior to movement initiation.
• Lengthened RTs may result from a combination of reduced suppression in some motor circuits and increased activity in others.
• Movement complexity directly influences corticospinal excitability during the preparatory phase of simple reaction time tasks.