TMS-induced phase resets depend on TMS intensity and EEG phase

Area of Science:

• Neuroscience
• Cognitive Science
• Biophysics

Background:

• Brain signal phase, particularly in electroencephalography (EEG), is crucial for cognitive functions.
• Transcranial Magnetic Stimulation (TMS) can noninvasively induce phase resets in neural oscillations.
• Understanding TMS parameters, like intensity and timing relative to brain phase, is key for effective stimulation.

Purpose of the Study:

• To investigate the relationship between TMS intensity and induced neural phase resetting.
• To explore how the endogenous phase of brain oscillations affects TMS-induced phase resetting.
• To guide the development of more precise and controllable TMS protocols.

Main Methods:

• A Transcranial Magnetic Stimulation-Electroencephalography (TMS-EEG) study was conducted.
• Single-pulse TMS was applied to the motor cortex at varying intensities.
• An autoregressive algorithm estimated the motor cortex's mu-alpha rhythm phase at the time of TMS delivery.

Main Results:

• TMS intensity parametrically influenced mu-alpha phase resetting and N100 amplitude compared to sham stimulation.
• Mu-alpha phase inversion was observed following TMS delivered near the peak of endogenous oscillations, but not troughs.
• Higher TMS intensities showed effects only when endogenous oscillations were near their peak phase.

Conclusions:

• Low-intensity TMS primarily resets existing neural oscillations.
• Higher-intensity TMS may activate silent neurons, contingent on the endogenous oscillation phase.
• Stimulation timing relative to ongoing brain activity can be manipulated to control TMS-induced phase resetting.