OBJECTIVES: This study examined the association between reward processing, as measured by performance on the probabilistic reversal learning (PRL) task and avoidance/rumination in depressed older adults treated with Engage, a psychotherapy that uses "reward exposure" to increase behavioral activation.

METHODS: Thirty older adults with major depression received 9 weeks of Engage treatment. At baseline and treatment end, the 24-item Hamilton Depression Rating Scale (HAM-D) was used to assess depression severity and the Behavioral Activation for Depression Scale (BADS) to assess behavioral activation and avoidance/rumination. Participants completed the PRL task at baseline and at treatment end. The PRL requires participants to learn stimulus-reward contingencies through trial and error, and switch strategies when the contingencies unexpectedly change.

RESULTS: At the end of Engage treatment, the severity of depression was lower (HAM-D: t(19) = -7.67, P < .001) and behavioral activation was higher (BADS: t(19) = 2.23, P = .02) compared to baseline. Response time following all switches (r(19) = -0.63, P = .003) and error switches (r(19) = -0.57, P = .01) at baseline was negatively associated with the BADS avoidance/rumination subscale score at the end of Engage treatment.

CONCLUSIONS: Impaired reward learning, evidenced by slower response following all switches and error switches, contributes to avoidant, ruminative behavior at the end of Engage therapy even when depression improves. Understanding reward processing abnormalities of avoidance and rumination may improve the timing and targeting of interventions for these symptoms, whose persistence compromises quality of life and increases the risk of depression relapse.