Modulation of plasticity in human motor cortex after forearm ischemic nerve block

Area of Science:

• Neuroscience
• Motor Control
• Brain Plasticity

Background:

• Deafferentation, or loss of sensory input, triggers cortical reorganization.
• This reorganization can be either beneficial or maladaptive, impacting motor function.
• Understanding how to modulate this plasticity is crucial for potential therapeutic interventions.

Purpose of the Study:

• To investigate whether deafferentation-induced cortical reorganization can be purposefully modulated.
• To examine the effects of different repetitive transcranial magnetic stimulation (rTMS) protocols on cortical plasticity following transient deafferentation.

Main Methods:

• Transient forearm deafferentation was induced using an ischemic nerve block (INB) in healthy participants.
• Five interventions were tested: INB alone, INB with ipsilateral rTMS (INB+rTMSi), rTMSi alone, INB with contralateral rTMS (INB+rTMSc), and rTMSc alone.
• Cortical plasticity was assessed using transcranial magnetic stimulation (TMS) to measure motor threshold (MT), motor evoked-potential (MEP) size, and intracortical inhibition/facilitation (ICI/ICF).

Main Results:

• INB alone moderately increased MEP size.
• INB+rTMSc significantly enhanced MEP size, reduced ICI, and increased ICF.
• INB+rTMSi blocked the INB-induced MEP increase, deepened ICI, and suppressed ICF.
• Single-session rTMS (ipsilateral or contralateral) did not alter plasticity parameters.

Conclusions:

• The deafferented motor cortex exhibits heightened modifiability.
• Cortical plasticity following deafferentation can be up-regulated by direct stimulation of the "plastic" cortex (contralateral rTMS).
• Plasticity can be down-regulated via inhibitory projections by stimulating the opposite cortex (ipsilateral rTMS).
• Noninvasive modulation of cortical plasticity offers potential for facilitating beneficial or suppressing maladaptive reorganization.