Long-interval cortical inhibition from the dorsolateral prefrontal cortex: a TMS-EEG study

Several studies have demonstrated that cortical inhibition (CI) can be recorded by paired transcranial magnetic stimulation (TMS) of the motor cortex and recorded by surface electromyography (EMG). However, recording CI from other cortical regions that are more closely associated with the pathophysiology of some neurological and psychiatric disorders (eg, dorsolateral prefrontal cortex (DLPFC) in schizophrenia) was previously unattainable. This study, therefore, was designed to investigate whether CI could be measured directly from the motor cortex and DLPFC by combining TMS with electroencephalography ( EEG). Long-interval CI ( LICI) is a TMS paradigm that was used to index CI in the motor cortex and DLPFC in healthy subjects. In the motor cortex, LICI resulted in significant suppression (32.8 +/- 30.5%) of mean cortical evoked activity on EEG, which was strongly correlated with LICI recorded by EMG. In the DLPFC, LICI resulted in significant suppression (30.1 +/- 26.9%) of mean cortical evoked activity and also correlated with LICI in the motor cortex. These data suggest that CI can be recorded by combining TMS with EEG and may facilitate future research attempting to ascertain the role of CI in the pathophysiology of several neurological and psychiatric disorders.