Figure 1.

Two axes conceptual framework for regulation of behavioral energy expenditure by dopamine. The horizontal axes represents dopamine's role in regulating generalized activity levels along a continuum from low activity (conserve) to high activity (expend). The vertical axes represent the role of dopamine in regulating the balance between exploration and exploitation by modulating the degree to which reward information biases the distribution of behavioral activity. “Dopamine function” is construed broadly here and may include not only extracellular concentrations of dopamine in target regions, activity of dopamine neurons (i.e., rate of tonic activity, prevalence of bursting) but also parameters such as relative expression of different receptors (e.g., D1 and D2), expression and activity of the doapmine transporter (DAT) as well as properties of vesicular release, including size of readily releaseable pool and vesicle size. As a general conceptual principle, we associate reduced dopamine function with conservation and exploitation (lower left quadrant) and increased dopamine function with expenditure and exploration (upper right quadrant), as reflected by the larger arrow. However, alterations of different aspects of the dopamine system (for example, shifting the relative expression of D1 and D2 receptors) may shift this relationship, generating behavior described by the other quadrants, such as high expenditure coupled with a greater exploitation of reward information (lower right quadrant).