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Orientation-specific fast rTMS maximizes corticospinal inhibition and facilitation
Tobias Tings1, Nicolas Lang, Frithjof Tergau
1Department of Clinical Neurophysiology, University of Göttingen, Robert-Koch-Str. 40, 37075, Göttingen, Germany.
Experimental Brain Research
|May 4, 2005
Summary
Monophasic repetitive transcranial magnetic stimulation (rTMS) is more effective than biphasic for modulating corticospinal excitability. Direction-specific currents induce transient facilitation or inhibition, with monophasic pulses maximizing these effects.
Area of Science:
- Neuroscience
- Neurophysiology
- Neuromodulation
Background:
- Repetitive transcranial magnetic stimulation (rTMS) can selectively modulate neuronal excitability.
- Monophasic stimulation may offer more precise control over neuronal excitation directionality compared to biphasic stimulation.
Purpose of the Study:
- To compare the efficacy of monophasic and biphasic rTMS in modulating corticospinal tract excitability.
- To investigate the effects of current direction (anterior-posterior vs. posterior-anterior) on rTMS-induced changes in motor evoked potential (MEP) amplitudes.
Main Methods:
- Ten healthy subjects received four types of rTMS over the primary motor cortex.
- Stimuli were monophasic or biphasic, with current directed antero-posteriorly or postero-anteriorly.
- rTMS parameters included 80 stimuli at 5 Hz, intensity set for 1 mV baseline MEP amplitude.
Main Results:
- Monophasic rTMS was consistently more efficient than biphasic rTMS in modulating MEP amplitudes.
- Anteriorly directed currents induced facilitation, while posteriorly directed currents induced transient inhibition (lasting ~30 pulses).
- Early inhibition was not observed during tonic muscle contraction.
Conclusions:
- Monophasic pulses are superior to biphasic pulses for maximizing directional effects in rTMS.
- The findings suggest specific neuronal circuit recruitment based on current polarity and direction.
- Biphasic rTMS effects can be attributed to the summation of opposing monophasic stimulations.