Delay discounting and reward sensitivity in a 2 x 2 study of bipolar disorder and alcohol dependence

Background and Aims Separate studies have shown increased delay discounting in people with bipolar disorder (BD) and people with alcohol dependence (AD) relative to people without mental health problems. Delay discounting was compared in people with no mental health problems, AD, BD and AD plus BD. Associations of delay discounting with self-reported impulsivity and reward sensitivity were also assessed. Design The study was a two-by-two factorial comparative observational design. Setting Data were collected at baseline diagnostic visits as part of a neuroimaging study at a medical university in South Carolina, USA. Participants Twenty-two BD + AD, 33 BD, 28 AD and 27 people without mental health problems participated. Measurements Diagnostic and clinician-rated symptom measures, self-report questionnaires and a computerized delay discounting task were administered. Two-by-two general linear univariate models were tested to examine between-group differences on discounting rates, and bivariate correlations and hierarchical regression analyses were performed to examine associations between discounting rates and self-reported reward sensitivity and impulsivity. Findings There was a significant main effect of AD (P = 0.006, eta(2) = 0.068). The main effect of BD and the BD x AD interaction terms were non-significant (P >= 0.293, eta(2) <= 0.010). Reward sensitivity and impulsivity were not significantly associated with discounting rates after adjustment for the other (P >= 0.089). Conclusions People with alcohol dependence appear to have higher delay discounting, while previously found associations between bipolar disorder and delay discounting may be secondary to alcohol use disorder.