Figure 1. Caudate Volumes: Partial Correlations with Verbal Learning and Depressive Symptoms.

A) Volumes of interests (VOIs) segmented from the Automated Anatomical Labeling (AAL) atlas are shown; note that the nucleus accumbens is included in the caudate VOI (yellow circle). B) Right caudate volumes were different across three groups (1-way ANCOVA, p= 0.035). Ketamine polysubstance (K+PolyS) users had the largest right caudates across groups, adjusted for age and sex. There was a linear trend in the right caudates, with K+PolyS>Primarily-K>Non-drug users (p=0.011). The two ketamine user groups combined also had larger right caudate volume than ND group (p=0.014). Adjusted p-values were derived from Tukey’s post hoc tests. In the left caudates, group difference across the three groups was also significant (p=0.047); Primarily-K users showed a trend for larger left caudates than ND controls (P=0.051). The two ketamine groups combined also had larger left caudates than ND controls (p=0.016). C) Across all participants (blue line), larger right caudate volumes showed a trend for correlation with better verbal learning (r=0.16, p=0.07), adjusted for age, sex and education. D) Among all ketamine users (brown line), but not the control subjects, larger right caudate volumes predicted with lower depressive symptom scores (Interaction-p=0.030; in ketamine users r=−0.28, p=0.013), adjusted for age and sex. NS=non-significant.