Optical illusion alters M1 excitability after mirror therapy: a TMS study

Area of Science:

• Neuroscience
• Motor Control
• Rehabilitation

Background:

• The contralesional primary motor cortex (M1) is implicated in motor recovery following mirror therapy.
• The role of ipsilesional M1 and its modulation by contralesional M1 via transcallosal interhemispheric inhibition (IHI) remains unclear.

Purpose of the Study:

• To investigate changes in IHI, intracortical inhibition, and intracortical facilitation of both M1s after mirror therapy using transcranial magnetic stimulation (TMS).
• To explore the neural mechanisms underlying motor improvements in the untrained hand during mirror therapy.

Main Methods:

• A 2x2 factorial design (time x group) with healthy subjects undergoing four days of standardized motor skill training.
• Two groups: a mirror group and a control group using a board.
• Transcranial magnetic stimulation (TMS) applied before and after training to assess M1 excitability and inhibition.

Main Results:

• The untrained hand showed significantly greater improvement in the mirror group compared to the control group (P = 0.02).
• Untrained hand improvement correlated with increased intracortical inhibition in the left M1.
• No significant differences in IHI were observed between groups or over time.

Conclusions:

• Confirms the involvement of the contralesional M1 in motor recovery after mirror therapy, independent of IHI.
• Different visual feedback during identical motor skill training engages distinct neural networks, highlighting training-induced plasticity.