High Beta Power in the Ventrolateral Prefrontal Cortex Indexes Human Approach Behavior: A Case Study.

Deep brain stimulation (DBS) of the ventral capsule and ventral striatum (VC/VS) is an effective therapy for treatment-resistant obsessive-compulsive disorder (trOCD). DBS initiation often produces acute improvements in mood and energy. These acute behavioral changes, which we refer to as "approach behaviors," include increased social engagement and talkativeness. We investigated the relationship between stimulation amplitude, spectral power in the ventrolateral prefrontal cortex (vlPFC), and speech rate in one male patient with trOCD implanted with bilateral VC/VS DBS leads and subdural electrodes adjacent to the orbitofrontal cortex and vlPFC. Several times over the first 24 weeks of therapy, we conducted experiments where we recorded data during epochs of high-amplitude or zero-/low-amplitude stimulation. We found that both the speech rate and vlPFC power in a high beta frequency band (31 ± 1.5 Hz, 1/f activity removed) increased during high-amplitude as compared with low-amplitude periods. The speech rate correlated with vlPFC high beta power. These effects were more consistent across time points in the left hemisphere than the right. At Week 24, we performed an experiment where stimulation was held constant, while the patient was asked to speak or remain silent. We showed that the presence or absence of speech was not sufficient to increase the vlPFC high beta power, suggesting stimulation is a key driver of the observed neurobehavioral phenomenon. Our results suggest vlPFC high beta power is a biomarker for approach behaviors associated with VC/VS DBS.