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Our research findings provide a direct functional link between the bursting activity of midbrain dopamine neurons and behavior. The research has significant applications for the improvement of health, because the dopamine neurons we are studying are the same neurons that become inactivated during Parkinson's Disease and with the consumption of psychostimulants such as cocaine and amphetamine

Midbrain dopamine neurons fire in two characteristic modes, tonic and phasic, which are thought to modulate distinct aspects of behavior. When an unexpected reward is presented to an individual, midbrain dopamine neurons fire high frequency bursts of electrical activity. Those bursts of activity allow us to learn to associate the reward with cues in our environment, which may predict similar rewards in the future.

When researchers placed the mice in reward-based situations, they found that the mice without the NMDA receptor in their dopaminergic neurons could not learn tasks that required them to associate sensory cues with reward. Those same mice, however, were able to learn tasks that did not involve an association with rewards.

Marc G. Berman and colleagues at the University of Michigan wanted to test the effect of a walk’s scenery on cognitive function (Berman, Jonides & Kaplan, 2008; PDF).

In the first of two studies participants were given a 35 minute task involving repeating loads of random numbers back to the experimenter, but in reverse order.

The results showed that people’s performance on the test improved by almost 20% after wandering amongst the trees. By comparison those subjected to a busy street did not reliably improve on the test.