Influences of current direction on 1 Hz motor cortex rTMS

Area of Science:

• Neuroscience
• Neuromodulation
• Motor Cortex Plasticity

Background:

• Repetitive transcranial magnetic stimulation (rTMS) effects are highly variable and lack replicability.
• Current direction is a known factor influencing rTMS aftereffects.
• Understanding these factors is crucial for optimizing rTMS protocols.

Purpose of the Study:

• To investigate the influence of current direction on cortical and peripheral markers of motor cortex plasticity induced by 1 Hz rTMS.
• To examine the correlation between cortical and peripheral markers.
• To identify potential confounding variables affecting rTMS outcomes.

Main Methods:

• Twenty-five healthy subjects received 2000 pulses of 1 Hz rTMS at 110% resting motor threshold.
• Stimulation was applied over the left motor hotspot in both anterior-posterior to posterior-anterior (AP-PA) and posterior-anterior to anterior-posterior (PA-AP) current directions.
• Motor evoked potentials (MEPs) and transcranial evoked potentials (TEPs) were assessed before and after rTMS using single pulses, with coil placement guided by a neuronavigated robot-assisted setup.

Main Results:

• 1 Hz rTMS induced higher amplitudes of MEPs and TEP components (N15, N45, P60) and reduced N100 amplitude.
• The PA-AP current direction elicited stronger effects on MEPs and TEPs compared to AP-PA.
• Latency changes (prolonged MEP and N15, shortened N100) were more pronounced with PA-AP stimulation.

Conclusions:

• Findings indicate facilitatory effects of 1 Hz rTMS, contrasting with inhibitory assumptions.
• Current direction significantly influences rTMS-induced plasticity, supporting the activation of distinct neuronal populations.
• Accurate reporting and control of stimulation parameters like current direction are essential for enhancing rTMS reliability and replicability.