Empirical validation of a touchscreen probabilistic reward task in rats

Area of Science:

• Neuroscience
• Behavioral Pharmacology
• Psychiatry

Background:

• Anhedonia, a core symptom of major depressive disorder (MDD), signifies a loss of pleasure and is a target for drug development.
• Quantitative measures of reward responsiveness are crucial for objectively assessing deficits and accelerating therapeutic interventions for mood disorders.
• The human probabilistic reward task (PRT) quantifies reward learning by assessing response bias towards more frequently rewarded stimuli.

Purpose of the Study:

• To validate a touchscreen-based rodent probabilistic reward task (PRT) with formal and functional similarity to the established human task.
• To assess the task's sensitivity to pharmacological manipulations and its utility as a preclinical assay for reward learning.

Main Methods:

• Rats were trained on a visual discrimination task involving two lines of differing lengths, with probabilistic reward contingencies.
• Parametric manipulations included varying reward probabilities, stimulus disparities, and administering drugs (amphetamine, scopolamine, oxycodone).
• Response bias and discriminability were measured to assess task performance and pharmacological effects.

Main Results:

• Rodent PRT performance showed orderly shifts in bias and discriminability based on reward asymmetry and stimulus differences.
• Reward-enhancing drugs (amphetamine, scopolamine) increased response bias, confirming task sensitivity; oxycodone did not.
• Task performance was successfully replicated in female rats, demonstrating broader applicability.

Conclusions:

• The touchscreen-based rodent PRT is a valuable preclinical tool for quantitatively assessing reward learning and anhedonia.
• This validated assay can significantly aid in the development of novel pharmacotherapies for neuropsychiatric conditions characterized by reward deficits.