The patients fell within the moderately to severely depressed range on the Montgomery-Åsberg Depression Rating Scale (score=18–45). There were no significant differences in age or IQ between the patients and comparison subjects (Table 1). The patients found significantly fewer locations (mean=2.4, SD=1.7) than the normal subjects (mean=3.8, SD=2.0) on the spatial navigation task (t=–2.70, df=47, p=0.01). There was no significant difference between men and women (t=–0.01, df=47, p=0.99). Among patients only, the number of locations found was correlated with the score on the Montgomery-Åsberg Depression Rating Scale (r=–0.33, N=30, p=0.02) such that the more severely depressed patients performed worse. For the subset of subjects (24 patients and 11 comparison subjects) who completed the Spatial Working Memory task, the number of locations found was correlated with overall task performance (r=–0.45, p=0.007). It was interesting, however, that there was no difference in scores on the Spatial Working Memory task between the patients (mean=33.3, SD=4.8) and comparison subjects (mean=33.4, SD=6.4) (t=–0.06, df=33, p=0.95), while there remained a performance difference on the virtual reality spatial navigation task within this subset (t=–2.36, df=33, p=0.03) whereby the patients found significantly fewer locations (mean=2.2, SD=1.5) than the normal comparison subjects (mean=4.0, SD=2.3). There were no differences between patients with and without a history of substance abuse on the outcome measures (number of locations found on the navigation task and performance on the Spatial Working Memory task). In post hoc comparisons of the three diagnostic groups (unipolar depressed, bipolar depressed, and healthy), there was no difference between the unipolar and bipolar depressed patients on navigation task performance. Finally, there was no difference on the navigation task between the bipolar depressed patients taking lithium and those taking valproic acid.