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GABA and cortical inhibition in motor and non-motor regions using combined TMS-EEG: a time analysis

Fitzgerald PB, Maller JJ, Hoy K, Farzan F, Daskalakis ZJ.

Objective: The induction of long interval cortical inhibition (LICI) in motor cortex with paired pulse transcranial magnetic stimulation (ppTMS) is an established paradigm for the assessment of cortical inhibition, proposed to be related to GABA(B) receptor inhibitory neurotransmission. This study aimed to further evaluate recent methods of the assessment of LICI in non motor regions with ppTMS and electroencephalography (EEG).

Methods: ppTMS was applied using a single coil to the motor and dorsolateral prefrontal cortex (DLPFC) in 14 healthy subjects, and in the parietal lobe in 5 of those subjects.

Results: In the motor cortex, LICI resulted in significant suppression in mean cortical evoked activity on EEG between 75 and 250 ms following delivery of the test stimulus. Maximal inhibition was seen from 50 to 250 ms in DLPFC, and between 50 and 175 ms in the parietal lobe.

Conclusions: ppTMS may be used to produce LICI in several cortical regions with a time course similar to known GABA(B) activity.

Significance: ppTMS induction of LICI can be recorded by combining TMS with EEG and seems to relate to GABA(B) activity.

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