A neurological messenger in the brain known as dopamine is described as the “feel-good” chemical related to reward and pleasure. Dopamine is present in the brain of humans and the brains of other animals, including mice. The purpose of the neurotransmitter is to carry signals between brain cells, and dopamine serves many functions, including aspects of cognitive processing. Dopamine has been studied extensively from the perspective of external cues known as deterministic signals. Researchers at the University of California San Diego investigated a less understood aspect related to spontaneous impulses of dopamine. The team found in the study that mice can willfully manipulate random dopamine pulses. Rather than occurring only when presented with pleasurable or reward-based expectations, researchers found the neural cortex in mice displayed with unpredictable impulses dopamine occurring approximately once per minute.
The team set out to investigate if the mice were aware that these impulses were occurring. The impulses were documented in the lab through molecular and optical imaging techniques. A feedback scheme was devised where mice on a treadmill received a reward if they show they were able to control impromptu dopamine signals. Researchers found that not only were the mice aware of the dopamine impulses, data gathered showed that the mice learned to anticipate and volitionally act upon a portion of them.
Researchers wrote in their study paper that critically, the mice learn to reliably elicit dopamine impulses before receiving a reward. The effects were reversed when the reward was removed. Researchers believe that spontaneous dopamine impulses may serve as a salient cognitive event in behavioral planning. Researchers believe the study opens a new dimension in the study of dopamine and brain dynamics.
In the future, the research will be extended to explore if and how unpredictable dopamine events drive foraging. Foraging activity is an essential aspect of the life of rodents in the wild for finding food, mates, and as a social behavior when colonizing new homes. The team believes the animals sense spontaneous dopamine impulses that could motivate them to search and forage in the absence of known reward-predictive stimuli.