Diego A. Pizzagalli Department of Psychology Harvard University
Recently, we described a probabilistic reward task based on a differential reinforcement schedule that allowed us to objectively assess participants’ propensity to modulate behavior as a function of reward history (Pizzagalli et al., 2005). In this 20-25-min computerized task, participants are confronted with a choice between two responses that are linked to different probabilities of reward. Due to this probabilistic design, participants cannot infer which stimulus is more advantageous based on the outcome of a single trial and so need to integrate reinforcement history over time in order to optimize their choices. Behavioral performance is analyzed using signal-detection theory by calculating both response bias toward the more frequently rewarded stimulus and overall discriminability (in addition to reaction time and hit rate). Unix scripts are available for automatic data quality check, outlier detection, and computation of behavioral variables.
In prior studies in non-clinical samples, subjects reporting elevated depressive symptoms showed reduced responsiveness to the more frequently rewarded stimulus (Pizzagalli et al., 2005). Moreover, reward responsiveness negatively correlated with self-reported anhedonic symptoms (Bogdan and Pizzagalli, 2006; Pizzagalli et al., 2005), and predicted these symptoms one month later (Pizzagalli et al., 2005). These findings have recently been extended to two clinical groups: euthymic patients with bipolar disorder (Pizzagalli et al., in press) and unmedicated subjects with unipolar depression (Pizzagalli et al., in press) were characterized by reduced reward learning and reward responsiveness, respectively.
In healthy controls, we have shown that reward responsiveness is reduced (1) under an acute stress condition (Bogdan and Pizzagalli, 2006); (2) by a pharmacological manipulation affecting the dopaminergic system (Pizzagalli et al., 2007a); and (3) in individuals reporting elevated stress appraisal (Pizzagalli et al., 2007b). Blunted reward responsiveness in participants receiving a dopaminergic challenge were simulated by reduced presynaptic DA signaling in response to reward in a neural network model of striatal-cortical function (Santesso et al., under review). Conversely, reward responsiveness was increased when a nicotine patch was applied to healthy non-smokers (Barr et al., in press). In addition, a preliminary study in monozygotic and dizygotic twins indicates that reward responsiveness has a substantial heritability component, with 45% of the variance explained by additive genetic components (Bogdan and Pizzagalli, under review). Finally, ongoing ERP and fMRI studies have provided preliminary evidence that response bias is associated with feedback-related negativity (FRN) and activation in the dorsal anterior cingulate and basal ganglia. A federal grant has been secured to develop a rodent model of our probabilistic reward task.
If you are interested in adopting the probabilistic reward task in your research, please email Dr. Pizzagalli (dap[at]wjh.harvard.edu).
Barr, R.S., Pizzagalli, D.A., Culhane, M.A, Goff, D.C., Evins, A.E. (in press). A single dose of nicotine enhances reward responsiveness in non-smokers: Implications for development of dependence. Biological Psychiatry, doi:10.1016/j.biopsych.2007.09.015.
Bogdan, R., Pizzagalli, D.A. (2006). Acute stress reduces hedonic capacity: Implications for depression. Biological Psychiatry, 60, 1147-1154.
Bogdan, R., Pizzagalli, D.A. (under review). The heritability of reward responsiveness and perceived stress: A twin study evaluation of depressive endophenotypes.
Pizzagalli, D.A., Bogdan, R., Ratner, K.G., Jahn, A.L. (2007b). Increased perceived stress is associated with blunted hedonic capacity: Potential implications for depression research. Behaviour Research and Therapy, 45, 2742-2753.
Pizzagalli, D.A., Evins, A.E., Schetter Cowman, E., Frank, M.J., Pajtas, P.E., Santesso, D.L., Culhane, M. (2007a). Single dose of a dopamine agonist impairs reinforcement learning in humans: Behavioral evidence from a laboratory-based measure of reward responsiveness. Psychopharmacology, doi:10.1007/s00213-007-0957-y
Pizzagalli, D.A., Goetz, E., Ostacher, M., Iosifescu, D., Perlis R.H. (in press). Euthymic patients with Bipolar Disorder show decreased reward learning in a probabilistic reward task. Biological Psychiatry.
Pizzagalli, D.A., Jahn, A.L., O'Shea, J.P. (2005). Toward an objective characterization of an anhedonic phenotype: A Signal-detection approach. Biological Psychiatry, 57, 319-327.
Pizzagalli, D.A., Iosifescu, D., Hallett, L.A., Ratner, K.G., Fava, M. (in press). Impaired hedonic capacity in major depressive disorder: A Signal-detection study. Journal of Psychiatric Research.
Santesso, D.L., Evins, A.E., Frank, M.J., Cowman, E.M., Pizzagalli, D.A. (under review). Single dose of a dopamine agonist impairs reinforcement learning in humans: Evidence from electrophysiology and computational modeling of striatal-cortical function.