Impulsivity and affective state
Interepisode subjects had mean SADS-C mania rating scale (MRS) score of 5.7 ± 4.6 (SD) and depression score of 7.9 ± 4.8; for manic subjects, MRS was 18.9 ± 6.7 and depression 8.7 ± 4.9; for depressed subjects, MRS was 4.6 ± 4.9 and depression 24.6 ± 4.9, and for mixed states, MRS was 17.9 ± 7.9 and depression score was 22.4 ± 7.3. Depression and mania scores did not correlate significantly (r = −0.09, p > 0.4). As shown in , BIS scores were increased in depressed, manic, and mixed, compared to interepisode, subjects, but the specific BIS-11 scores that were increased depended on affective state. Motor impulsivity appeared to be selectively related to mania, nonplanning impulsivity more strongly related to depression, and attentional impulsivity similarly, and additively, related to both. No interactions between depressive and manic states approached significance. Post hoc analysis showed that elevations in motor, attentional, and total impulsivity scores were associated with the manic state, being higher in manic than in interepisode subjects and higher in mixed than in depressed subjects. Nonplanning impulsivity was higher in depressed or mixed than in interepisode subjects.
BIS scores and affective state
Substance abuse can have prominent effects on impulsivity and its relationship to bipolar disorder (Swann et al., 2004
). The 27 subjects who had never met criteria for a substance use disorder resembled the entire group, with noninteracting main effects of depression and mania for total (F(mania) = 11.9, p = 0.0022); F(depression)=6, p = 0.022; F(interaction) =0)), attentional (F(mania) =6.9, p=0.015; F(depression)=5.6, p = 0.026); F(interaction)=0) and nonplanning impulsivity (F(mania)=5.6, p = 0.027; F(depression)=8.1, p = 0.009; F(interaction)=0.9). Motor impulsivity was significantly increased in mania (F(mania)=15, p = 0.0008), without a main effect of depression (F(depression)=1.1). Unlike the case with all subjects, both mania and depression had significant main effects on nonplanning impulsivity in subjects without histories of substance use disorders. Results of post hoc analyses in subjects without histories of a substance use disorder were essentially identical to the case for the entire group, except that the difference in Motor impulsivity between manic and interepisode subjects was significant rather than being a trend.
Among subjects who had definitely met criteria for a substance use disorder, there were no significant effects of affective state on BIS scores (for main effects, F < 1.8, for interactions, F < 0.8). Among all subjects, with substance use disorder added to the ANOVA model, there were significant interactions between mania and substance abuse history for BIS total (F(1,63) = 4.6, p = 0.035) and motor score (F(1,63) = 5.7, p = 0.02), reflecting a higher BIS score in interepisode subjects, and a smaller difference between manic and interepisode subjects, with a history of a substance use disorder (for BIS total score in subjects without histories of a substance use disorder, interepisode 62.1 ± 13 vs manic 75.0 ± 9.1; for those with definite substance use disorder history, interepisode 81.1 ± 13.4 vs manic 84.3 ± 11.8). MRS in interepisode subjects did not differ between those without (6.7 ± 4.8) and with (5.1 ± 4.4) histories of a substance use disorder (t (df=21) = 0.5), so the higher BIS scores in interepisode subjects with histories of substance use disorders were not due to higher residual mania scores.
Differential relationships between impulsivity and depression or mania
Multiple regression analysis, with BIS scores as dependent variables and depression and mania scores as independent variables, showed that both depression and mania scores contributed significantly to BIS total and attentional scores. Mania, but not depression, contributed to BIS motor scores, while depression, but not mania, contributed to BIS nonplanning scores. summarizes the data for the 27 subjects who had never met criteria for a substance use disorder. The entire group of 74 subjects, including the 47 with a substance use disorder, had exactly the same pattern of significant relationships. When age of onset, substance use history, and treatment with antipsychotic medicines, lithium, anticonvulsants, and antidepressants were taken into account, the same relationships as those in persisted.
Multiple linear regression analyses of BIS, depression, and mania subscale scores in subjects with bipolar disorder but without substance use disorders
Impulsivity and affective symptoms
In order to investigate relationships between individual depressive or manic symptoms and impulsivity, we conducted a principal components analysis of SADS-C items to determine which symptoms contributed most to depression and mania in these subjects. After varimax rotation, four factors accounted for over half the variance. The factors were 1) Depression, consisting, in order of strength of loading, subjective depression, anhedonia, hopelessness, negative self-evaluation, worry, fatigue, somatic anxiety, self-reproach, and suicidality (eigenvalue 5.2, 20.2% of variance); 2) Mania, consisting of increased energy, elevated mood, visible hyperactivity, accelerated speech, grandiosity, increased goal-directed activity, decreased need for sleep, and racing thoughts (eigenvalue 5.9, 18.9% of variance); 3) Psychosis, consisting of delusions, hallucinations, and paranoia (eigenvalue 2.3, 8.8% of variance); and 4) Hostility, consisting of overt irritability, overt anger, and subjective irritability (eigenvalue 2.2, 8.4% of variance).
For all subjects (n=74), attentional impulsivity correlated significantly with depression (r=0.28, p = 0.015) and mania factor (r = 0.25, p = 0.03) scores, motor impulsivity correlated with mania factor scores (r = 0.24, p = 0.04) and nonplanning impulsivity correlated with depression factor scores (r = 0.24, p = 0.04). There were no significant correlations between BIS scores and hostility or psychosis factor scores. For subjects without history of a substance use disorder (n=27), attentional impulsivity correlated significantly with depression (r = 0.42, p = 0.03) scores, motor impulsivity correlated with mania scores (r = 0.39, p = 0.04), and nonplanning impulsivity correlated with depression scores (r = 0.44, p = 0.02). The pattern of multiple regression correlation coefficients for the mania and depression factors was exactly the same as that shown in for mania and depression subscale scores.
We then investigated relationships between BIS scores and the rating scores for the symptoms loading most strongly to depression or mania, in all subjects having an episode, depressed subjects, and manic subjects. shows that, among manic symptoms in all subjects having episodes, visible hyperactivity correlated most strongly with BIS scores. There were significant but more modest correlations with increased energy and accelerated speech. In manic episodes, visible hyperactivity correlated significantly with attentional (Kendall tau = 0.306) and motor (Kendall tau = 0.265) scores; no other symptoms correlated with BIS scores. Visible hyperactivity was also the only manic symptom correlating with BIS scores among depressed subjects, where it correlated significantly with total (Kendall tau = 0.424), attentional (Kendall tau = 0.408) and motor scores (Kendall tau = 0.408).
Correlations between manic or depressive symptoms and BIS scores
As was the case with mania, subjective depressive mood itself did not correlate with BIS scores. Hopelessness and anhedonia correlated significantly with BIS attentional scores in all subjects and in subjects experiencing manic episodes. Suicidality also correlated modestly but significantly with BIS attention scores for subjects in depressive or manic episodes (Kendall tau = 0.175, p = 0.03) and in all subjects (Kendall tau = 0.192, p = 0.02).