Background. Cognitive behavioural therapy (CBT) has been implemented in bipolar (BP) disorder with varying degrees of success. The link between CBT for BP disorder and underlying theory is not clear. There have been attempts to identify a unique style of dysfunctional thinking in BP disorder analogous to that in unipolar (UP) disorder but this has suffered from a dearth of prospective studies controlling for mood and phase of illness. In this prospective study, we have examined whether dysfunctional thinking and the (dys)regulation of traumatic memories are trait vulnerability factors in BP versus UP mood disorders.

Method. BP-1 and UP groups were followed-up from acute episode to recovery, and compared with a healthy control group. Measures of dysfunctional thinking and linked personality dimensions were taken, together with measures assessing autobiographical memory retrieval (AMT). The presence and control of intrusive memories of traumatic events in BP and UP disorder were assessed.

Results. Controlling for mood symptoms and phase of illness, the BP (but not the UP) group was largely indistinguishable from controls on dysfunctional thinking. Intrusive memories of traumatic events were present in 45% of the BP and 48% of the UP groups; and those without intrusions were more overgeneral on the AMT in all phases of illness.

Conclusion. These findings are in line with the ‘affect regulation’ hypothesis for UP disorder and deliberate self-harm. This may help in understanding the mode of action of CBT in BP disorder and to further improve the therapy, primarily through the promotion of affective regulation, which is one component of the complex CBT intervention for BP disorder.