Local brain-state dependency of effective connectivity: a pilot TMS-EEG study

Area of Science:

• Neuroscience
• Brain Stimulation
• Electrophysiology

Background:

• Spontaneous cortical oscillations modulate responses to transcranial magnetic stimulation (TMS).
• The influence of these oscillations on cortical effective connectivity remains largely unexplored.
• This pilot study investigates the impact of spontaneous oscillations on TMS-evoked potentials (TEPs).

Purpose of the Study:

• To investigate how spontaneous cortical oscillations affect cortical effective connectivity.
• To establish a foundation for future research on phase-dependent TMS effects.
• To explore the relationship between neural oscillations and TMS-induced neural activity.

Main Methods:

• TMS was applied to the left primary motor cortex and right pre-supplementary motor area in three subjects.
• Electroencephalography (EEG) was used to record brain activity.
• Trials were classified based on the phase of mu and beta rhythms, and differences in global mean-field amplitude (GMFA) and cortical spreading of TEPs were analyzed.

Main Results:

• Global mean-field amplitude (GMFA) was significantly affected by oscillation phase in 4 out of 12 datasets.
• Significant phase effects on GMFA were observed at various time points post-stimulus (before 50 ms, 50–100 ms, and after 100 ms).
• Source estimation revealed complex spatial differences in the cortical spreading of TMS-evoked activity between phase classes.

Conclusions:

• Cortical effective connectivity, as measured by TMS-evoked potentials, appears to be dependent on the phase of local cortical oscillations.
• This study provides crucial insights for developing future closed-loop brain stimulation strategies.
• The findings highlight the importance of considering ongoing neural oscillations in TMS research.