To examine frequency specific communications between the medial prefrontal cortex (mPFC) and subthalamic nucleus (STN) during conflict processing.

Growing evidence suggests that conflict processing involves a ‘hyperdirect’ pathway in the frontosubthalamic network. Yet how the frontosubthalamic circuit coordinates its activities during conflict processing remains poorly understood. Recent computational, electrophysiological, and clinical studies have implicated two brain areas in frontosubthalamic network as being crucial during conflict processing: the mPFC and STN. Both structures exhibit increased low frequency (2-8 Hz) activities during conflict that correlates with the amount of time taken to respond. This suggests that the two sites could become functionally coupled during conflict.

We simultaneously recorded from the mPFC with EEG and STN with local field potentials from deep brain stimulation electrodes in 10 Parkinson’s Disease patients while they performed a Stroop task. Time-Frequency spectrum, intertrial phase locking, phase coherence and phase-amplitude coupling (PAC) were analyzed in this study.

1. We observed significant increase in theta (2-8 Hz) as well as non-significant increase in gamma (32-64 Hz) activity in both mPFC and STN during incongruent trials.

2. Both mPFC and STN theta activities demonstrate phase reset and enhanced theta phase coherence between the two sites.

3. Robust increased PAC (P=0.002) between theta phase and gamma amplitude was found in the STN in incongruent trials, and this theta-gamma coupling was stronger (P=0.004) for incongruent trials with shorter reaction times. Moreover, there is a negative correlation between theta-gamma coupling and reaction times in incongruent trials (r=-0.59, P=0.01).

The combination of PAC and long-range phase synchronization may play a role in large-scale communications in the brain. Cortico-subcortical circuits might coordinate their activities in the low-frequency range to engage stimulus-related processing in higher frequencies via the combination of long-range, within-frequency phase synchronization and local cross-frequency PAC.