Cortical inhibition on TMS-EEG: interstimulus interval effect on short-interval paired-pulse

Area of Science:

• Neuroscience
• Cognitive Science
• Psychiatry

Background:

• Paired-pulse (PP) transcranial magnetic stimulation and electroencephalography (TMS-EEG) are increasingly used to assess cortical inhibition in motor and nonmotor brain regions for mental disorders.
• Short-interval cortical inhibition (SICI) is a key measure, typically studied in the motor cortex, but its application and optimal parameters in nonmotor regions like the dorsolateral prefrontal cortex (DLPFC) are less understood.

Purpose of the Study:

• To investigate the effect of different interstimulus intervals (ISIs) on SICI in the DLPFC.
• To compare the efficacy of 2ms and 4ms ISIs in characterizing TMS-EEG signals (P60 and N100 amplitudes and latencies) over the DLPFC.

Main Methods:

• A pilot study involving six subjects performing a SICI protocol over the DLPFC.
• Utilized TMS-EEG to record brain responses at ISIs of 2ms and 4ms.
• Analyzed TMS-evoked potentials (TEPs), specifically the P60 and N100 components, for amplitude and latency variations.

Main Results:

• A trend towards greater cortical inhibition was observed with a 2ms ISI compared to a 4ms ISI, particularly for the N100 component (p ≈ 0.05).
• The P60 component showed no significant variation in cortical inhibition between the tested ISIs.
• Findings align with existing data from motor cortex studies, suggesting a similar inhibitory pattern.

Conclusions:

• A 2ms ISI appears more effective for assessing cortical inhibition in the DLPFC using SICI protocols.
• This finding has clinical relevance, potentially improving the assessment of DLPFC function in mental health evaluations.
• Further research with larger sample sizes is recommended to confirm these preliminary results.