As people grow older, the desire to learn and engage in daily activities often dwindles.
That phenomenon, which Psychology Benefits Society said psychologists refer to as anhedonia, could appear when people no longer wish to pursue old hobbies, such as gardening, or if they do continue a hobby, they don’t maintain it.
A recent study of mice from researchers at the Massachusetts Institute of Technology found a brain circuit that is critical for maintaining motivation so something such as anhedonia does not occur.
In the study, which was published Tuesday in the journal “Cell,” neuroscientists examined what happens in striosomes. These play critical roles in a variety of behaviors. They’re also major parts of the forebrain component, basal ganglia, which plays an important role in reinforcement learning. Researchers studied striosomes as mice learned to make emotional decisions. To do that, they measured and analyzed the activity of striosomes while mice learned to pick between negative or positive results.
The experiment saw mice hear two different tones. Sugar water served as a reward with one tone. The other tone was joined by a bright light, which served as a mildly aversive stimulus. Slowly, the mice learned if they licked the spout more upon hearing the first tone, more sugar water came. By licking less when hearing the second tone, they found the light would shine less brightly.
As the mice learned the task, scientists found striosomes displayed more activity than other parts of the striatum, a main input area for the basal ganglia. This activity was associated with the mice’s behavioral responses to both tones, suggesting striosomes might be crucial for attaching subjective value to a certain result.
“A person, or this case a mouse, may value a reward so highly that the risk of experiencing a possible cost is overwhelmed, while another may wish to avoid the cost to the exclusion of all rewards," said lead author and MIT research scientist Emily Hueske in a press release. "And these may result in reward-driven learning in some and cost-driven learning in others.”
Then, scientists discovered mice who were roughly equivalent in age to people in their 60s and up had decreased engagement in learning this sort of cost-benefit analysis. Compared to younger mice, their striosomal activity declined simultaneously. A similar loss of motivation had been found in a mouse experiment of Huntington’s disease, a neurodegenerative disorder that affects the striatum and its striosomes.
Using genetically targeted medications to increase activity in the striosomes, researchers noticed the mice became more engaged in doing the task. When striosomal activity was suppressed, however, mice were disengaged.
Currently, researchers are working on potential medicinal remedies that could arouse this circuit. Teaching patients to enhance activity in this circuit through biofeedback could offer a possible potential way to enhance their cost-benefit evaluations, researchers suggest.
“If you could pinpoint a mechanism which is underlying the subjective evaluation of reward and cost, and use a modern technique that could manipulate it, either psychiatrically or with biofeedback, patients may be able to activate their circuits correctly,” said Alexander Friedman, a former MIT research scientist who is now an assistant professor at the University of Texas at El Paso and also a lead author of the study.
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