Behavioral Activation System (BAS) differences in bipolar I and II disorder

A growing body of evidence supports the Behavioral Activation System (BAS) dyresgulation model of bipolar disorder, however its application to bipolar II disorder is limited. The current study examines its potential relevance to bipolar I and II disorders. We specifically sought to determine whether bipolar sub-types would differ in terms of BAS sensitivity, and examined for differential prospective relationships between BAS sensitivity and bipolar I and II symptom expression.

Participants were recruited from the Sydney-based Black Dog Institute. Diagnostic groups were derived on the basis of agreement between clinician and DSM-IV diagnoses from structured interviews. Baseline measures of BAS sensitivity, mood symptoms and anxiety were completed. Self-rated mood was assessed over a 6-month period. Clinician-rated mood status was re-assessed at follow-up to determine the predictive utility of BAS scores.

The sample comprised 151 bipolar participants (69 bipolar I, 82 bipolar II). BAS-Drive and Reward Responsiveness scores were significantly higher in bipolar I disorder participants. BAS sub-scale scores were uniquely positively associated with mood variability in bipolar I and II disorder. BAS-Drive and Reward Responsiveness scores were positively associated with bipolar I hypo(mania), and with the former also positively associated with bipolar II depression. BAS scores did not predict bipolar I or II mood episode status at 6-month follow-up.

BAS sensitivity was self-reported; inability to establish independence of BAS scores from residual symptoms; lack of controlling for medication effects; inability to determine the influence of life events; length of follow-up period may have not been sufficient to evaluate the predictive utility of BAS sensitivity for mood episodes or detect course of illness differences across bipolar sub-types.

Differences in BAS sensitivity and associations with mood variability were quantified in bipolar I and II disorder, suggesting the need for tailored treatments for these separate conditions. Further investigation of the role of the BAS in bipolar sub-types is warranted.