The exact function of the anterior cingulate cortex (ACC) is one of the largest riddles in cognitive neuroscience and a major challenge in mental health research. ACC dysfunction contributes to a broad spectrum of neurological and psychiatric disorders, such as depression, ADHD, Parkinson's disease, OCD and many others, but nobody knows what it actually does. Recently a new theory has been developed about ACC function; the HRL-ACC (Hierarchical Reinforcement Learning Theory of ACC). This theory proposes that the ACC selects and motivates high-level tasks based on the principles of hierarchical reinforcement learning. The ACC associates values with tasks, selects the correct tasks and applies control over other neural networks (such as the dorsolateral prefrontal cortex and basal ganglia), which execute the tasks. The values of these tasks are attributed based on reward prediction error signals, which are sent from the midbrain dopamine system to the ACC. These signals can be recorded using scalp-EEG as an event-related brain potential (ERP), which is called the reward positivity. Until this day, the exact origin of the reward positivity is not yet known. Studies have delivered strong indirect evidence that the reward positivity is generated in the ACC. However, there is an important lack of direct evidence to support this hypothesis. The goal of this study is to provide direct evidence that the reward positivity is generated in the ACC by letting a group of patients with refractory epilepsy perform the virtual T-maze task (which is known to elicit reward positivity) and simultaneously recording intracranial video-EEG.