Human hippocampal dynamics during response conflict

Besides its relevance for declarative memory functions [1-5], hippocampal activation has been observed during disambiguation of uncertainty and conflict [6,7]. Uncertainty and conflict may arise on various levels. On the perceptual level, the hippocampus has been associated with signaling of contextual deviance [8-10] and disambiguation of similar items (i.e. pattern separation) [11-13]. Furthermore, conflicts can occur on the response level. Animal experiments showed a role of the hippocampus for inhibition of prevailing response tendencies and suppression of automatic stimulusresponse
mappings [14-17], potentially related to increased theta oscillations (3-8Hz) [18]. In humans, a recent functional magnetic resonance imaging (fMRI) study demonstrated hippocampal involvement in approach-avoidance conflicts [19]. However, the more general significance of hippocampal activity for dealing with response conflicts also on a cognitive level is still unknown. Here, we investigated the role of the hippocampus for response conflict in the Stroop task by combining intracranial electroencephalography (iEEG) recordings from the hippocampus of epilepsy patients with region of interest-based fMRI in healthy participants. Both methods revealed converging evidence that the hippocampus is recruited in a regionally-specific manner during response conflict. Moreover, our iEEG data show that this activation depends on theta oscillations and is relevant for successful response conflict resolution.