Researchers from the Massachusetts Institute of Technology (MIT) discovered a new link between the motivation of learning new things and aging. The study by MIT neuroscientists was recently published in the journal Cell using a Huntington's Disease model.
Using engineered mice models, the team discovered a brain circuit associated with the motivation of learning. The circuit is also involved in decision-making as the brain evaluates the cost and reward of actions.
During the study, older mice that had the brain circuit activated had increased motivation to learn. They discovered that the opposite was also true when the circuit was suppressed.
Professor Ann Graybiel said, "As we age, it's harder to have a get-up-and-go attitude toward things." Engaging behavior is an essential factor for people's social well-being and learning. It is difficult to learn without attending or engaging with others.
Brain Circuits and Consequences
The basal ganglia contains brain circuits associated with forming habits, movement, emotions, and addiction. This brain region contains the striatum composed of cell clusters called striosomes. Years ago, Graybiel discovered striosomes but had not determined their function due to their size and location in the brain, which remained difficult to capture using functional magnetic resonance imaging (fMRI).
In recent years, the researchers discovered that striosomes are involved in approach-avoidance conflict, one form of making decisions. Unlike the fight or flight instincts, the decisions involve taking good and bad consequences or avoiding the situation altogether.
For example, the approach-avoidance conflict mechanism kicks in when given a job offer with better pay but is far away from close friends and family. On the negative side, these decisions can trigger anxiety.
Graybiel had previously linked striosomes to cells in a brain center that produces dopamine, suggesting that they could be gatekeepers of sensory and emotional information that determine how people decide how to act. Such actions may be complemented by cells producing dopamine.
Emotional Decision-Making
Stress was also observed to have a significant impact on the brain circuit involved with emotional decision making. In 2017 lab experiments, stressed rats and mice would take higher risks if the brain circuit was blocked or suppressed.
In the new study, the mice were stimulated by tones and a bright light with sugar water as a reward. They learned that licking the spout more after hearing the first tone meant that they would receive more sugar water. If they licked the spout less after the second tone, the bright light would be dimmer.
Alexander Friedman said, "In order to survive, in order to do whatever you are doing, you constantly need to be able to learn. You need to learn what is good for you, and what is bad for you."
In older mice, striosomal activity was significantly lower than younger mice. The decline of motivation was similar to Huntington's disease, a neurodegenerative illness associated with the striatum. Friedman said that identifying how the brain evaluatees reward and cost could help patients activate their brain circuits correctly.
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