Interhemispheric interactions between the right angular gyrus and the left motor cortex: a transcranial magnetic...

Area of Science:

• Neuroscience
• Motor Control
• Cognitive Neuroscience

Background:

• Goal-directed hand movements depend on the posterior parietal cortex (PPC) and motor cortex (M1).
• Previous transcranial magnetic stimulation (TMS) studies suggest complex interactions between the right PPC and left M1 (LM1).
• The precise role of right PPC-mediated inhibition on left PPC-LM1 interactions remains unclear.

Purpose of the Study:

• To investigate how combined stimulation of the right and left angular gyri (AG) within the PPC influences LM1 excitability.
• To elucidate the mechanisms underlying the interaction between the AG and LM1 in motor control.

Main Methods:

• Utilized paired-pulse TMS in 16 healthy subjects with MRI-guided neuronavigation targeting bilateral AG.
• Assessed the effects of right AG (RAG) and left AG (LAG) stimulation on LM1 excitability, short-interval intracortical facilitation (SICF), short-interval intracortical inhibition (SICI), and long-interval intracortical inhibition (LICI).

Main Results:

• RAG stimulation alone facilitated LM1, inhibited SICF, and reduced the influence of LAG on LM1 (LAG-LM1).
• Combined RAG-LAG stimulation did not alter SICI but significantly increased LICI.
• RAG-mediated inhibition of LAG-LM1 was linked to reduced indirect (I)-wave activity and enhanced GABA_B receptor-mediated inhibition in LM1.

Conclusions:

• The right angular gyrus plays a crucial role in modulating motor cortex excitability and inhibitory processes.
• RAG influences LM1 through both ipsilateral connections (via LAG) and direct heterotopic connections.
• Combined RAG-LAG stimulation enhances GABA_B-mediated inhibition in the left motor cortex, highlighting novel neural interactions.