For successful goal-directed behavior, a performance monitoring system is essential. It detects behavioral errors and initiates behavioral adaptations to improve performance. Two electrophysiological potentials are known to follow errors in reaction time tasks: the error-related negativity, which is linked to error processing, and the error positivity, which is associated with subjective error awareness. Furthermore, the correct-related negativity is linked to uncertainty about the response outcome. Here we attempted to identify the involvement of the nucleus accumbens in the aforementioned performance monitoring (...) processes. To this end, we simultaneously recorded cortical activity and local field potentials during a flanker task performed by four patients with severe opioid abuse disorder who underwent electrode implantation in the NAc for deep brain stimulation. We observed significant accuracy-related modulations in the LFPs at the time of the ERN/CRN in two patients and at the time of Pe in three patients. These modulations correlated with the ERN in 2/8, with CRN in 5/8 and with Pe in 6/8, recorded channels, respectively. Our results demonstrate the functional interrelation of striatal and cortical processes in performance monitoring specifically related to error processing and subjective error awareness. (shrink)