Hippocampal and orbitofrontal theta band coherence diminishes during conflict resolution.

OBJECTIVE Coherence between the hippocampus and other brain structures has been shown with the theta frequency (3-8 Hz). Cortical decreases in theta coherence are thought to reflect response accuracy efficiency. However, the role of theta coherence during conflict resolution is poorly understood in non-cortical areas. In this study, coherence between the hippocampus and orbitofrontal cortex (OFC) was measured during a conflict resolution task. While both brain areas have been previously implicated in the Stroop task, their interactions are not well understood. METHODS Nine patients were implanted with SEEG contacts in the hippocampus and OFC. Local field potential data were sampled throughout discrete phases of a Stroop task. Coherence was calculated for hippocampal and OFC contact pairs, and coherence spectrograms were constructed for congruent and incongruent conditions. Coherence changes during cue processing were identified using a non-parametric cluster-permutation t-test. Group analysis was conducted to compare overall theta coherence changes between conditions. RESULTS In six out of nine patients, decreased theta coherence was observed only during the incongruent condition (p < 0.05). Congruent theta coherence did not change from baseline. Group analysis demonstrated lower theta coherence for the incongruent condition compared to the congruent condition (p < 0.05). CONCLUSION Theta coherence between the hippocampus and orbitofrontal cortex decreased during conflict. This finding supports existing theories that theta coherence desynchronization contributes to improved response accuracy and processing efficiency during conflict resolution. The underlying theta coherence observed between the hippocampus and OFC during conflict may be distinct from its previously observed role in memory.