[Triad TMS of Human Motor Cortex].

Area of Science:

• Neuroscience
• Neurophysiology
• Neurology

Background:

• Cortical excitability is crucial for motor control.
• Understanding intrinsic rhythmic activity in the primary motor cortex (M1) is key to diagnosing neurological disorders.
• Existing methods for assessing cortical excitability have limitations.

Purpose of the Study:

• To develop and validate a novel method, triad-conditioning stimulation (TCS), for investigating intrinsic rhythmic activity in the primary motor cortex (M1).
• To assess changes in M1 rhythmic activity in healthy volunteers and patients with specific neurological conditions.

Main Methods:

• Developed triad-conditioning stimulation (TCS), involving three sub-threshold conditioning transcranial magnetic stimulation (TMS) pulses followed by a supra-threshold test stimulus.
• Administered TCS at various intervals to healthy volunteers and patients with cortical myoclonus, Parkinson's disease, and amyotrophic lateral sclerosis.
• Measured motor evoked potentials (MEPs) to assess cortical excitability and identify frequency-dependent facilitation patterns.

Main Results:

• Healthy volunteers exhibited significant MEP facilitation at a 25ms interval (40Hz), suggesting an intrinsic M1 rhythm.
• Cortical myoclonus patients lacked facilitation at 25ms but showed facilitation at 40ms (25Hz), consistent with known abnormal beta rhythms.
• No significant facilitation at 25ms was observed in Parkinson's disease or amyotrophic lateral sclerosis patients.

Conclusions:

• Triad-conditioning stimulation (TCS) effectively probes intrinsic rhythmic activity in the primary motor cortex (M1).
• TCS can differentiate rhythmic activity patterns in healthy individuals versus those with specific neurological disorders like cortical myoclonus.
• This method offers a promising tool for investigating M1 network dynamics and aiding in the diagnosis of neurological conditions.