LAUSR

Adaptive decision making requires the adjustment of behavior following an error in order to improve future performance, but obsessive compulsive disorder (OCD) patients are characterized by abnormal error monitoring [1,2]. For example, in cognitive tasks like Flanker or Stroop, reaction time (RT) following commission of an error (post-error; PE) is often longer than that of RT following a correct response (post-correct; PC), but this phenomenon, known as PE slowing (PES), is inordinate in OCD patients (e.g. [1]). PES is associated with increased theta activity over the medial prefrontal cortex (mPFC) [3], and PES of OCD patients was shown to be mainly driven by abnormally slow PC RTs rather than a failure to slow down after errors [1]. Notably, a recent study [4] has demonstrated that acute theta transcranial alternating current stimulation over the mPFC of healthy volunteers induced short-term reductions of PES without compromising post-error accuracy (PEA) in the Flanker task. Given the notion that the effects of stimulation may accumulate over repeated sessions [5], it is plausible that multiple stimulation sessions of the mPFC may induce long-term modifications to cognitive functions associated with error monitoring [5]. To test this notion, we revisited data from a study recently published in Brain Stimulation [6], which compared the efficacy of 5 weeks of high-frequency active or sham deep transcranial magnetic stimulation (dTMS) over the mPFC as a treatment for OCD. The study included a Stroop task and electrophysiological recording administered before the first and before the last treatment sessions. The Stroop task was specifically designed to probe Error Response Negativity (ERN) in the clinical setting (i.e., short duration, but promoting sufficient errors rates in repeated tests). The task was divided into 10 blocks of alternating stimulus-response mapping (10 practice þ 80 test trials each), making response selection lessautomatic. Participants were requested to respond as accurate but as fast as possible and limited (1200m s) catch trials were scattered randomly (10% of trails) to impose this instruction. Preand Posttreatment Stroop data was available for 12 patients of the active group (7 females) and 10 patients of the sham group (7 females). Gender was used as a covariate in all analyses due to earlier reports on gender differences in brain responses to errors and post-error adjustments [7] as well as gender differences in responses to dTMS observed in the original study [6]. First, analysis of total RT distribution (PC þ PE) was conducted using extraction of percentiles (5, 25, 50, 75, 95) from the RT distribution of each individual during incongruent trials (where response selection is most challenging) [7]. These were subjected to ANOVA with Percentiles X Time (pre/post treatment) X