Subsecond Changes in Top–Down Control Exerted by Human Medial Frontal Cortex during Conflict and Action Selection: A Combined Transcranial Magnetic Stimulation–Electroencephalography Study

Abstract

Action selection requires choosing one of all the possible conflicting action plans that are available. There is currently a debate as to whether the dorsal medial frontal cortex (dMFC) merely detects or actively resolves response conflict. We used combined on-line transcranial magnetic stimulation and electroencephalographic recording (TMS-EEG) to test whether human dMFC plays a critical causal role in conflict resolution, and whether the mechanism for such a function is via interactions with primary motor cortex. In an Eriksen flanker task, subjects discriminated the direction of the centermost arrow in an array of five, responding with the left or right hand. The lateralized readiness potential (LRP), a measure of relative levels of activity in left and right motor cortices, was also recorded. Reaction times and error rates were higher on incongruent than congruent trials, and incongruent trials produced a positive LRP deflection reflecting initial partial activation of the incorrect response. On one-half of trials, repetitive TMS was applied to left dMFC starting 100 ms before visual stimulus onset and ending 100 ms afterward. TMS disrupted performance by selectively increasing error rates on contralateral (right hand) incongruent trials. TMS also only modulated the LRP on incongruent trials, causing an increased positive deflection (associated with preparation of the incorrect response) starting 180 ms after visual stimulus onset. TMS of a control site did not interfere with behavior or motor cortical activity. dMFC has a direct causal role in resolving conflict during action selection, and the mechanism involves the top-down modulation of primary motor cortical activity.

Posterior Medial Frontal Cortex Activity Predicts Post-Error Adaptations in Task-Related Visual and Motor Areas

“…This corroborates our result showing that pMFC activity predicts the strengths of motor activity following errors, i.e., stronger pMFC activity leads to less motor activity in the post-error trial. Furthermore, a disruption of medial frontal activity by TMS leads to stronger activations of the incorrect response in the motor system in an interference task (Taylor et al, 2007).…”

Stimulation of the Frontal Eye Field Reveals Persistent Effective Connectivity after Controlled Behavior

“…They were clustered at the coordinate (30,2,57) in the standard brain of the Montreal Neurological Institute (MNI), which corresponds to the FEF (Ford et al, 2005;Grosbras et al, 2005;Brown et al, 2007). In the control experiment, the procedure was as above with the exception that we delivered TMS to the postcentral gyrus (mean coordinate: 28, Ϫ42, 66), following the procedure of a previous TMS-EEG study (Taylor et al, 2007b). The TMS intensity was fixed at 35% of the maximum stimulator output.…”

Theta burst magnetic stimulation over the pre-supplementary motor area improves motor inhibition

“…Conflict between competing actions has also previously implicated the pre-SMA [60][61][62]. To causally influence conflict resolution, it is possible that more extensive stimulation of the full SMA complex, including both the SMA and pre-SMA [63], is required.…”