Depressive patients are more impulsive and inconsistent in intertemporal choice behavior for monetary gain and loss than healthy subjects--an analysis based on Tsallis' statistics.

OBJECTIVES Depression has been associated with impaired neural processing of reward and punishment. However, to date, little is known regarding the relationship between depression and intertemporal choice (delay discounting) for gain and loss. This examination is potentially important for advances in neuroeconomics of intertemporal choice, because depression is associated with reduced serotonergic activities in the brain. DESIGN AND SETTING We compared impulsivity and inconsistency in intertemporal choice for monetary gain and loss between depressive patients and healthy control subjects. METHODS We conducted delay discounting tasks for gain and loss in depressed and healthy control subjects. We then quantified impulsivity and inconsistency in the delay discounting with parameters in the q-exponential discount function based on Tsallis' statistics. RESULTS We observed that depressive patients were more impulsive and time-inconsistent in intertemporal choice action for gain and loss, in comparison to healthy controls. MAIN FINDINGS Depressed patients were more irrational in temporal discounting. CONCLUSIONS The usefulness of the q-exponential discount function for assessing the impaired decision-making by depressive patients was demonstrated. Furthermore, biophysical mechanisms underlying the altered intertemporal choice by depressive patients are discussed in relation to impaired serotonergic neural systems.