From the thrill of hearing an ice cream van approaching to the peaks of joy over a fine wine, the neurological messenger known as dopamine has been popularly described as the brain’s “feel good” chemical associated with reward and pleasure.
Dopamine, a ubiquitous neurotransmitter that carries signals between brain cells, is involved in several aspects of cognitive processing among its many functions. The chemical messenger has been studied extensively from the perspective of external cues or “deterministic” signals. Instead, researchers at the University of California San Diego recently set out to investigate less understood aspects related to spontaneous impulses of dopamine. Their results, published July 23 in the journal Current biology, have shown that mice can intentionally manipulate these random dopamine pulses.
Rather than just appearing on pleasant or reward-based expectations, Conrad Foo, a PhD student at UC San Diego, led research that found that the neocortex in mice is flooded with unpredictable dopamine pulses that occur roughly once a minute.
In collaboration with colleagues from UC San Diego (Department of Physics and Section of Neurobiology) and the Icahn School of Medicine at Mount Sinai in New York, Foo investigated whether mice actually know that these impulses – in the laboratory, molecularly and optically documented imaging procedures – actually occur. The researchers developed a feedback scheme in which mice on a treadmill were rewarded for showing that they were able to control spontaneous dopamine signals. The data showed that not only were mice aware of these dopamine impulses, but the results also confirmed that they learned to anticipate part of it and to respond to it willingly.
“It is crucial that mice have learned to reliably trigger (dopamine) impulses before they receive a reward,” the researchers write in the paper. “These effects were reversed when the reward was removed. We posit that spontaneous dopamine impulses can serve as a pre-eminent cognitive event in behavior planning.”
The researchers say the study will open a new dimension in research into dopamine and brain dynamics. They now intend to expand this research to investigate whether and how unpredictable dopamine events drive foraging, which is an essential aspect of foraging, partnering, and social behavior in colonizing new home bases.
“We further suspect that the feeling for spontaneous dopamine impulses could motivate an animal to search and forage for food in the absence of known reward-predicting stimuli,” the researchers found.
In their efforts to control dopamine, the researchers made it clear that dopamine appears to enliven rather than initiate motor behavior.
“This started as the chance discovery of a talented and curious PhD student with the intellectual support of a wonderful group of colleagues,” said David Kleinfeld, lead co-author of the study, professor in the Department of Physics (Division of Physical Sciences) and Section Neurobiology (Division of Biological Sciences). “As an unexpected result, we spent many long days expanding the original study and of course doing control experiments to verify the claims. These led to the current conclusions.”
Materials provided by University of California – San Diego. Originally written by Mario Aguilera. Note: The content can be edited in terms of style and length.