Feel good brain messenger: Neuroscientists have shown that mice can learn to manipulate random dopamine impulses to obtain rewards.

The neurological messenger known as dopamine has been described as a “Feel good” brain chemical associated with reward and pleasure, from elation at the sound of an approaching ice cream truck to bursts of pleasure when sipping fine wine.

A ubiquitous neurotransmitter that transmits signals between brain cells, dopamine, in addition to its many functions, is involved in many aspects of cognitive activity. This chemical messenger has been widely studied in terms of external signals, or “deterministic” signals. Instead, researchers at the University of California, San Diego recently set out to study the less understood aspects associated with spontaneous dopamine impulses. Their results, published July 23 in the journal Current Biology, showed that mice can deliberately manipulate these random dopamine impulses.

San Diego State University graduate student Conrad Fu led the study, which found that mice’s neocortex is flooded with unpredictable dopamine pulses that occur about once a minute.

Working with colleagues at the University of California, San Diego (Department of Physics and Section of Neurobiology) and the Icahn School of Medicine at Mount Sinai in New York, Fu investigated whether the mice were aware that these pulses — recorded in the lab using molecular and optical imaging techniques — were actually happening. The researchers devised a feedback circuit in which mice on a treadmill were rewarded if they showed they could control impromptu dopamine signals. The findings showed that the mice were not only aware of these dopamine impulses, but also confirmed that they had learned to anticipate and voluntarily act on part of them.

“Very importantly, the mice learned to reliably elicit (dopamine) impulses before receiving a reward,” the researchers noted in their paper. “These effects reversed when the reward was removed. We hypothesize that spontaneous dopamine impulses may serve as a meaningful cognitive event in planning behavior.”

According to the researchers, the study opens up a new dimension in the study of dopamine and brain dynamics. They now intend to expand this study to see if unpredictable dopamine events contribute to foraging, which is an important aspect of finding sustenance, mate search and social behavior in colonizing new habitats.

“We also hypothesize that sensing spontaneous dopamine impulses may induce animals to search and forage in the absence of known stimuli that portend reward,” the researchers noted.

Trying to control for dopamine, the researchers specified that dopamine appears to stimulate rather than initiate motor behavior.

“It all started with an unexpected finding by a talented and inquisitive graduate student with the intellectual support of a wonderful group of colleagues,” said senior study co-author David Kleinfeld, professor in the Department of Physics (Department of Physical Sciences) and the Neurobiology Section (Department of Biological Sciences). “As a result of unforeseen efforts, we spent many long days extending the original study and, of course, conducting control experiments to test the claims. This led to the present conclusions.”

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