480 Effect of Chronic DBS on Ventral Capsule Ventral Striatum-Specific Circadian Rhythm in Refractory Obsessive-Compulsive Disorder

INTRODUCTION: Deep brain stimulation (DBS) of the ventral capsule/ventral striatum (VC/VS) improves symptoms in ∼66% of patients with treatment-resistant obsessive-compulsive disorder (OCD). However, a common adverse effect of VC/VS DBS is hypomania, marked by decreased need for sleep and increased risk-taking behaviors. Modern DBS devices have enabled 24-hour collection of neural data, allowing for tracking of circadian rhythms reflected by VC/VS local field potentials (LFPs). METHODS: We implanted six patients with treatment-resistant OCD with a DBS device configured for constant VC/VS stimulation and recording. Spectral power in the 9 ± 2.5 Hz band was estimated onboard the device every 10 minutes for a median of 249 days (range 77-608). We assessed the rhythmicity of power in this spectral band by fitting 7-day retrospective rolling windows of per-day normalized LFP power to cosine functions using least-squared regression. Output metrics included acrophase (time of peak activity), amplitude, and fit significance. We quantified trends in acrophase over time using Pearson correlation. RESULTS: All six patients demonstrated consistent 24-hour cyclic LFP activity bilaterally. Two of the six had diurnal peaks which shifted significantly earlier across the study period. The remaining four patients had nocturnal peaks, all shifting significantly later over time. Notably, a patient in the latter group experienced three days of hypomania after DBS initiation associated with circadian disruptions even after clinical symptom resolution. Only after clinical DBS adjustment 2 weeks later did circadian rhythm rapidly return to pre-hypomanic levels. CONCLUSIONS: Study patients demonstrated evolving circadian VC/VS LFP activity across the course of DBS therapy, usually independent of cyclic whole-brain activity (i.e. sleep). Conversely, disruptions to these circadian patterns, as observed here during hypomania, may serve as biomarkers of region-specific stimulation side effects.