Triad TMS of the human motor cortex

Area of Science:

• Neuroscience
• Motor Control
• Neurology

Background:

• Traditional methods like local field potentials have limitations for studying cortical rhythms due to small EEG amplitudes.
• Transcranial magnetic stimulation (TMS) offers a non-invasive approach to probe brain activity.
• Investigating the intrinsic rhythm of the primary motor cortex (M1) is crucial for understanding motor control and neurological disorders.

Purpose of the Study:

• To introduce and review the triad-conditioning TMS (TCS) technique for assessing the intrinsic rhythm of the human primary motor cortex (M1).
• To explore the frequency dependency of M1's rhythmic activity using TCS.
• To investigate potential abnormalities in M1 rhythm in conditions like cortical myoclonus and Parkinson's disease (PD).

Main Methods:

• Developed a triad-conditioning TMS (TCS) technique involving three subthreshold conditioning stimuli followed by a suprathreshold test stimulus.
• Recorded motor evoked potentials (MEPs) from the first dorsal interosseous (FDI) muscle.
• Compared MEPs elicited by TCS at various intervals with a control condition (test stimulus alone) in healthy volunteers and patients.

Main Results:

• In healthy volunteers, a 25 ms interval (40 Hz) TCS induced MEP facilitation, suggesting an intrinsic M1 rhythm.
• In cortical myoclonus, a 40 ms interval (25 Hz) TCS induced facilitation, consistent with previously reported abnormal M1 rhythms.
• In Parkinson's disease, a 25 ms interval TCS did not evoke facilitation, indicating altered rhythmic activity.

Conclusions:

• Triad-conditioning TMS (TCS) is a viable method for investigating the intrinsic rhythmic activity of the human primary motor cortex (M1).
• The TCS technique can differentiate between normal and abnormal M1 rhythmic patterns observed in neurological disorders.
• This method holds promise for diagnosing and understanding motor cortex dysfunction in various conditions.