The right inferior frontal cortex in response inhibition: A tDCS-ERP co-registration study

In any given common situation, when an individual controls him/herself or obeys and stops a current action when asked to do, it is because the brain executes an inhibitory process. This ability is essential for adaptive behaviour, and it is also a requirement for accurate performance in daily life. It has been suggested that there are two main inhibitory functions related to behaviour, as inhibition is observed to affect behaviour at different time intervals. Proactive inhibition permits the subject to control his behavioural response over time by creating a response tendency, while reactive inhibition is considered to be a process that usually inhibits an already initiated response. In this context, it has been established that inhibitory function is implemented by specific fronto-basal-ganglia circuits. In the present study, we investigated the role of the right inferior frontal cortex (rIFC) in response inhibition by combining into a single task the Go-NoGo task and the Stop-Signal task. Concurrently, we applied transcranial direct current stimulation (tDCS) over the IFC and recorded electroencephalography (EEG). Thus, we obtained online EEG measurements of the tDCS-induced modifications in the IFC together with the participant's performance in a response inhibition task. We found that applying bilateral tDCS on the IFC (right anodal/left cathodal) significantly increased proactive inhibition, although the behavioural parameters indicative of reactive inhibition were unaffected by the stimulation. Finally, the inhibitory-P3 component reflected a similar modulation under both inhibitory conditions induced by the stimulation. Our data indicates that an online tDCS-ERP approach is achievable, but that a tDCS bilateral montage may not be the most efficient one for modulating the rIFC.