Characterizing long interval cortical inhibition over the time-frequency domain

Area of Science:

• Neuroscience
• Cognitive Neuroscience
• Neurophysiology

Background:

• Long-interval cortical inhibition (LICI) is a neurophysiological measure assessed using combined transcranial magnetic stimulation (TMS) and electroencephalography (EEG).
• Previous studies have primarily focused on LICI within specific cortical regions, potentially overlooking its broader spatiotemporal influence.

Purpose of the Study:

• To investigate extended dimensions of LICI characteristics in both time-frequency and spatial domains.
• To introduce and evaluate novel amplitude measures for LICI signal analysis: Discrete Fourier Transform (DFT) and Hilbert Transform (HT).
• To compare the topographical patterns of single and paired pulse responses in LICI.

Main Methods:

• LICI was elicited using single and paired TMS pulses targeting the motor cortex (MC) and dorsolateral prefrontal cortex (DLPFC).
• TMS-EEG data were collected from 33 healthy participants.
• LICI signal amplitude was quantified using both DFT and HT, measuring the difference between unconditioned and conditioned cortical activity.

Main Results:

• Both DFT and HT revealed significant differences between unconditioned and conditioned evoked activity in both MC and DLPFC (p<0.0001).
• The inhibitory influence of LICI was found to be significantly larger in both spatial and temporal extent than previously documented.
• Distinct differences in intensity and topographical patterns were observed between single and paired pulse conditions.

Conclusions:

• DFT and HT provided comparable results, confirming the efficacy of these novel amplitude measures.
• Cortical inhibition, as measured by LICI, exhibits a complex and extended spatiotemporal profile.
• LICI can be detected with high sensitivity in cortical areas distant from the stimulation site, suggesting significant clinical and research applications for understanding inhibition/excitation in various states.