Tonic dopamine modulates exploitation of reward learning

Area of Science:

• Neuroscience
• Behavioral Science
• Computational Neuroscience

Background:

• The role of dopamine in adaptive behavior, particularly tonic dopamine, remains under-explored in naturalistic settings.
• Existing research suggests phasic dopamine is key for reinforcement learning, while tonic dopamine may modulate performance without affecting learning itself.

Purpose of the Study:

• To quantitatively assess the function of tonic dopamine in adaptive behavior using a semi-naturalistic instrumental task.
• To investigate how altered dopamine levels impact learning and behavioral expression in mice.

Main Methods:

• Utilized a "closed economy" paradigm where DAT knockdown mice (hyperdopaminergic) and wild-type mice earned food by lever pressing.
• Introduced frequently shifting relative costs for food rewards on different levers.
• Applied reinforcement learning models to analyze lever choice data and distinguish between learning acquisition and expression.

Main Results:

• Hyperdopaminergic mice worked harder, pressing levers with higher costs more frequently, to maintain body weight.
• Both groups demonstrated rapid responses to changes in lever costs, indicating intact change detection.
• Reinforcement learning models revealed normal learning from reward history but a reduced ability to utilize this learning in hyperdopaminergic mice.

Conclusions:

• Tonic dopamine modulates the expression of learned behaviors by influencing the coupling between prior learning and action selection.
• Altered dopamine levels impact motivated behavior by affecting how learned information guides choices, rather than the learning process itself.