To develop reliable, valid, and efficient measures of
obsessive-compulsive disorder (OCD) severity, comorbid
depressionseverity, and total electrical energy delivered (TEED) by deep
brain stimulation (DBS), we trained and compared random
forestsregression models in a clinical trial of participants receiving
DBS for refractory OCD. Six participants were recorded during
open-endedinterviews at pre- and post-surgery baselines and then at
3-month intervals following DBS activation. Ground-truth severity
wasassessed by clinical interview and self-report. Visual and auditory
modalities included facial action units, head and facial
landmarks,speech behavior and content, and voice acoustics.
Mixed-effects random forest regression with Shapley feature reduction
stronglypredicted severity of OCD, comorbid depression, and total
electrical energy delivered by the DBS electrodes (intraclass
correlation,ICC, = 0.83, 0.87, and 0.81, respectively. When random
effects were omitted from the regression, predictive power decreased
tomoderate for severity of OCD and comorbid depression and remained
comparable for total electrical energy delivered (ICC = 0.60,0.68, and
0.83, respectively). Multimodal measures of behavior outperformed ones
from single modalities. Feature selection achievedlarge decreases in
features and corresponding increases in prediction. The approach could
contribute to closed-loop DBS that wouldautomatically titrate DBS based
on affect measures