Paradoxical enhancement of choice reaction time performance in patients with major depression

The Cued Reinforcement Reaction Time (CRRT) task is a choice reaction time task in which rewards (points) are available if the subject responds quickly enough and are signalled with a certain probability by stimuli. Reaction times (RTs) are faster following stimuli predicting reward with a high probability than with a low probability. This RT difference is sensitive to manipulations and individual differences in the serotonin (5-HT) system, but the CRRT task performance has not yet been examined in patients with depression. We observed that patients performed better on the task than controls, as evidenced by a greater points score, a greater likelihood of reaching their reinforcement threshold and fewer errors. RT variability was reduced in the patients. No group differences in the effect of the conditioned stimuli on RTs were observed. Accounts of these surprising data are discussed, considering possible effects of antidepressant medication or task-dependent differences in selective attention. Regardless of precise mechanism, the results do indicate that depressed patients are not invariably impaired in motivational paradigms and that their RT performance in certain situations can be superior to that of controls.