There are no particular sensory receptors through which the brain is specifically informed about the occurrence of a reward event or object. Thus the brain cannot identify a reward from the activation of a neural "labeled reward line." The brain needs to extract the reward information through its own neural mechanisms.

“Major obstacles were our lack of understanding of the relations between the surprising findings and the well-established behavioral theories of reward, hence my motivation to write this paper.”

To investigate this we need to define what a reward is, and this should be based on behavior. Ideally, the same definition would hold for vegetative rewards, like food, liquid, and sex, as well as for more elaborate rewards, like money that we use for daily decisions.

The paper describes some of the basic behavioral theories relating to reward, namely animal learning theory from experimental psychology, and utility theory from microeconomics. Through neuroscience it connects entirely different scientific disciplines.

The paper describes a way to understand reward functions based on a synthesis of knowledge, developed over more than a hundred years.

If you want to investigate how the brain processes reward function, you need to know what functions rewards have. The functions described in the paper are based on measurable behavior rather than subjective states of pleasure, which makes the research more objective and allows it to be carried out in neurobiological experiments in animals.

We tried to find a motor function in dopamine neurons that would correspond to the motor deficits in Parkinsonian patients with degenerated dopamine neurons—and we completely failed. We found something funny: a dopamine response to a piece of apple irrespective of movements, and then to liquid, and then the response disappeared when the food or liquid were predicted by a stimulus, and then we found a different signal in dopamine neurons related to the uncertainty of rewards when we probed for basic parameters of utility theory. Subsequent research discovered reward signals in a few other brain structures, such as the basal ganglia, frontal cortex, and amygdala.

A podcast audio interview with Prof. Wolfram Schultz discusses the neuromechanisms involved in going after a reward and how the brain processes reward function. Podcast formats: mp3 | wma

Major obstacles were our lack of understanding of the relations between the surprising findings and the well-established behavioral theories of reward, hence my motivation to write this paper. We also had people rightly questioning whether animals felt pleasure every time they received 0.01 milliliters of juice, 500 times a day, which led us to consider objective measures of reward functions, such as learning, approach behavior, and preferences described by the behavioral theories.

The research field of reward is currently exploding. My next interests are uncertainty coding and decision-making at the level of single neurons, but also human brain imaging on reward issues that are difficult to investigate in animals, such as higher-order rewards, individual differences for reward and risk, and social relations.

Better understanding of brain processes related to reward and uncertainty has implications for economic decision-making and the understanding and treatment of reward abuse in such disorders as drug addiction, overeating, and gambling.

Medical implications would relate to dysfunctions in which reward and the brain’s reward centers play a role, including learning deficits, attention deficit disorder, schizophrenia, and Parkinson’s disease.

For economics, research on reward might help to understand the biological basis for exceptions to standard utility theory and "irrational" decision making.