Motor cortex excitability changes during imagery of simple reaction time

Area of Science:

• Neuroscience
• Motor Control
• Human Physiology

Background:

• Motor imagery enhances cortical motor excitability.
• The inhibition of motor execution during imagined movements may influence cortical excitability.
• Understanding differences between real and imagined movements is crucial for motor control research.

Purpose of the Study:

• To investigate differences in motor-evoked potential (MEP) facilitation and short-interval intracortical inhibition (SICI) reduction between real and imagined simple reaction time tasks (SRT).
• To explore the temporal dynamics of cortical excitability changes before movement onset during real and imagined SRT.
• To assess the potential of motor imagery as a rehabilitative tool by comparing its effects on corticospinal excitability with actual movements.

Main Methods:

• Thirteen healthy volunteers performed real (rSRT) and imagined (iSRT) visual simple reaction time tasks.
• Motor-evoked potentials (MEPs) and short-interval intracortical inhibition (SICI) were measured using transcranial magnetic stimulation (TMS) at various time intervals before expected movement onset.
• Electromyographic (EMG) signals from the first dorsal interosseous (FDI) muscle were recorded to determine movement onset.

Main Results:

• Both rSRT and iSRT significantly increased MEPs compared to rest, with rSRT showing facilitation at -50 and -25 ms, and iSRT at -50 ms.
• SICI was significantly reduced during both rSRT (at -75, -50, -25 ms) and iSRT (at -50, -25 ms) before EMG onset.
• Complete removal of SICI was observed only in rSRT shortly before EMG onset, indicating a difference in intracortical inhibition between real and imagined actions.

Conclusions:

• Motor imagery increases corticospinal excitability and decreases intracortical inhibition, mirroring temporal patterns of real movements.
• The complete suppression of SICI is specific to actual motor execution, highlighting a key difference from motor imagery.
• These findings suggest that motor imagery, while enhancing excitability, may serve as a valuable tool in motor rehabilitation for individuals with movement limitations.