Repeated-measures ANOVA revealed a highly significant effect of trial over the five learning blocks (F=184.2, df=4, 324, p<0.0001) but no effect of group (F=1.41, df=2, 81, p=0.25) or group-by-time interaction (F=0.96, df=8, 234, p<0.47). One-way ANOVAs also indicated no significant group effects on immediate or delayed recall or recognition (t2). In the group of relatives of patients with bipolar I disorder, higher scores on the Hamilton depression scale were associated with lower California Verbal Learning Test learning scores (trials 1–5 total) (r=–0.46, df=22, p=0.03). The association with Hamilton depression scale scores was not significant in the group of euthymic patients with unipolar depression (r=–0.35, df=15, p<0.21), although these correlations did not differ significantly between the two groups (Fisher’s test, z=–0.391, p>0.05).
Six of 27 relatives of patients with bipolar I disorder failed to complete the task (two intradimensional shifting, two extradimensional shifting, two extradimensional reversal), and four of 15 euthymic patients failed to complete the task (one compound discrimination, one intradimensional reversal, two extradimensional shifting). All comparison subjects completed the task. Task completion rates differed significantly between groups (χ2=12.8, df=2, p=0.002), and at the extradimensional shifting stage specifically (χ2=6.23, df=2, p<0.05). Analysis of error rates confirmed a significant group difference in total task errors, which was also significant at the extradimensional shifting stage (t2). The main effects of group remained significant after we covaried for gender (total errors F=4.01, df=2, 85, p=0.02, and extradimensional shifting errors F=5.99, df=2, 85, p=0.004). There were no group differences in reversal errors or intradimensional shifting errors. Post hoc comparisons using Tukey’s honestly significant difference indicated that relatives of patients with bipolar I disorder made more extradimensional shifting errors than comparison subjects (p=0.02) and euthymic patients made more extradimensional shifting errors than comparison subjects (p<0.03). The subset of relatives of patients with bipolar I disorder without a personal history of affective disturbance (N=16) also showed more extradimensional shifting errors than comparison subjects (the relatives’ mean=6.8, SD=9.5) (t=2.55, df=61, p=0.01). There was no difference in the euthymic patients receiving (N=6) or not receiving (N=9) antidepressant medication (t=0.61, df=13, p<0.56). Total errors did not correlate with Hamilton depression scale scores in the relatives of patients with bipolar I disorder (r=0.18, df=27, p<0.37) or euthymic patients (r=0.12, df=15, p=0.68).