The role of the anterior cingulate cortex in inhibitory control - ACDC TMS study

Background: Inhibitory control is a cognitive function, part of the “executive functions" group, representing our ability to choose and regulate how we react and behave rather than being hostages of habit. Impaired inhibitory control plays a role in neuropsychiatric disorders' pathophysiology, such as drug and alcohol abuse, gambling, eating disorders, or obsessive‐compulsive disorder (OCD). Previous studies have associated cognitive control with neural activity in the anterior cingulate cortex (ACC) (1). The data suggest that the dorsal ACC is critically involved in the “response selection" and that deficient activity in this region represents a common element across psychiatric disorders (2). Double cone coil transcranial magnetic stimulation (DC TMS) is an instrument for non‐invasive brain stimulation, which, unlike the classic rTMS, is useful for reaching deeper targets, such as the ACC (3). ACDC TMS was used in trials with a patient population (OCD, major depressive disorder), but only one study with healthy subjects used high‐frequency ACDC TMS to study cognitive control. However, it addressed the problem of gambling and the specific “delay discounting" phenomenon was tested (4). We evaluated the effect of ACDC TMS on inhibitory control using the classic Stroop paradigm and aimed to answer whether it is possible to affect the "healthy" inhibitory control. Methods: In a randomised, double‐blind, sham‐controlled study with healthy participants (n = 21) with the parallel design, we assessed the effect of ACDC TMS on Stroop test performance. Healthy volunteers received active 20Hz ACDC TMS or sham TMS. Right before and after the stimulation participants took the computer‐based Stroop test. During the stimulation, participants performed the PASAT for the activation of the inhibitory control circuit. To examine the impact of stimulation on reaction time and error scores Wilcoxon rank sum test was used. Results were considered significant if they exceeded a p‐05. Results: Nineteen participants completed the study, two participants had headaches and nausea and were forced to end the experiment. No significant effect of ACDC TMS condition on reaction times was observed either in congruent (W = 57, p = 0.84) or incongruent (W = 30, p‐value = 0.1214) trials. No significant effects on error rates were detected as well (W= 35.5, p = 0.46). Conclusions: The study is still ongoing. The preliminary results showed no significant effect of ACDC TMS on inhibitory control in healthy participants. It can be explained by the small group size, and possible ceiling effect (all participants were medical students or doctors with a high level of education). The absence of a significant result can also be explained by ACDC TMS's inability to affect the functioning inhibitory control circuit.