Reviewed by Danielle Ellis, B.Sc.Aug 9 2023 Researchers have long thought that rewards like food or money encourage learning in the brain by causing the release of the "feel-good" hormone dopamine, known to reinforce storage of new information. Now, a new study in rodents describes how learning still occurs in the absence of an immediate incentive.
To provide some clarity, the study authors focused on when and under what circumstances dopamine levels are high at the same time as acetylcholine levels are low. They found that this situation occurs frequently, even in the absence of rewards. In fact, it turns out that the hormones constantly ebb and flow in the brain, with dopamine levels regularly raised while acetylcholine levels are low, setting the stage for continual learning.
As expected, the drink treats created the typical patterns of dopamine and acetylcholine release that are prompted by rewards. However, the team also observed that well before receiving water treats, dopamine and acetylcholine already followed "ebb and flow" cycles approximately twice every second, during which the levels of one hormone dipped while the other surged. Dr. Krok notes that this pattern continued regardless of whether the rodents were running or standing still.
Related StoriesIn schizophrenia, for example, patients often experience delusions that contradict reality. If the dopamine-acetylcholine circuit is constantly strengthening connections in the brain, says Dr. Tritsch, then problems with this mechanism might lead to the formation of too many, and incorrect, connections, causing them to "learn" of events that did not really occur.