Cortical Inhibition in Motor and Non-Motor Regions: A Combined TMS-EEG Study

Abstract

A number of studies using paired pulse transcranial magnetic stimulation (TMS) have demonstrated that cortical inhibition (CI) of the motor cortex can be recorded and also gauged through surface electromyography. However, recording CI from other brain regions that are more directly related with the pathophysiology of some neurologic and psychiatric disorders (e.g., dorsolateral prefrontal cortex (DLPFC) in schizophrenia) was previously fraught with technical difficulties. This study was therefore designed to examine, through a combination of TMS with EEG, whether CI could be measured directly from the motor cortex, DLPFC, and another non-motor region. To index CI, long interval cortical inhibition (LICI; a TMS paradigm) was used in the motor cortex and DLPFC in 14 healthy subjects, and in the parietal lobe in 5 of those subjects. In the motor cortex, LICI resulted in a significant suppression in mean cortical evoked activity on EEG (37.31 +/- 47.51%). In the DLPFC, LICI resulted in a significant suppression (32.45 +/- 47.86%) in mean cortical evoked activity and did not correlate with LICI in the motor cortex although they did not significantly differ. In the parietal lobe, LICI resulted in significant suppression (47.76 +/- 44.70%) in mean cortical evoked activity. In conclusion, CI in the dorsolateral prefrontal cortex, motor cortex and parietal cortex were similar at 120% of motor threshold. 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 neurologic and psychiatric disorders.

Investigating TMS–EEG Indices of Long-Interval Intracortical Inhibition at Different Interstimulus Intervals

“…Using TMS-EEG, several studies have shown that LICI is associated with reduced excitability in both motor and nonmotor areas of cortex [23,[39][40][41]. For the primary motor cortex, the magnitude of this inhibition correlates with inhibition of the MEP, demonstrating the involvement of mechanisms comparable to those reflected by conventional LICI measurements.…”

Characterization of Glutamatergic and GABAA-Mediated Neurotransmission in Motor and Dorsolateral Prefrontal Cortex Using Paired-Pulse TMS–EEG

“…However, the ability to noninvasively investigate SICI and ICF in other areas would be highly desirable, for example, in prefrontal areas, which are more directly involved in cognitive disorders (Julkunen et al, 2011). Recent technical advances have enabled the concurrent recording of electroencephalographic (EEG) responses to TMS (Ilmoniemi and Kicic, 2010), thus providing a potentially more direct measure of induced changes in neuronal activity and extending the use of TMS to non-motor areas Fitzgerald et al, 2008). Such studies have demonstrated EEG neurophysiological correlates of cortical inhibitory circuits such as GABA B -mediated longinterval intracortical inhibition (LICI) in motor and dorsolateral prefrontal cortex (DLPFC) Fitzgerald et al, 2008).…”

The effect of rTMS over the inferior parietal lobule on EEG sensorimotor reactivity differs according to self-reported traits of autism in typically developing individuals

“…Electroencephalogram (EEG) was recorded through a 64-channel Synamps2 EEG system (Compumedics, Neuroscan, Texas, USA) and concurrently TMS was delivered over the EEG cap according to previously published methods Fitzgerald et al, 2008). Eye movements were recorded using four facial electrodes (above and below the left eye and on the outer canthi of the eyes).…”