Feeling unmotivated to learn new skills as you get older? Researchers from the University of Queensland believe your aging brain structure may be to blame. According to their findings, published in the journal Neuron, a key circuit in the brain that’s responsible for learning through goal attainment, may deteriorate with age.

"Flexibility issues in aging have long been described in other navigation and spatial memory tasks,” said the study’s lead author J. Bertran-Gonzalez, a postdoctoral research fellow at the University of Queensland, in a statement. “Here we describe a similar flexibility problem but applied to goal-directed action, which of course has more detrimental consequences for everyday life and potentially compromises survival. This flexibility problem could constitute a first step towards major motivational decline and, in some cases, seed further cognitive conditions and dementia.”

For the study, researchers placed a group of young and older mice inside a chamber and trained them to press two different levers, each one containing a different reward. Lever one released a grain-flavored food pellet, while lever two released a sweet-flavored pellet. After they learned how to receive their desired food pellets using the levers, they were placed in another chamber that gave them open access to only the plain-flavored pellets. Once the mice had spent an hour eating as much grain-flavored pellets as they wanted, researchers placed them back into the first chamber where both old and young mice chose the lever with the sweet-flavored pellets.

Next, researchers reversed the levers. The first one released sweet-flavored pellets instead of grain-flavored pellets, and the second lever now released grain-flavored pellets instead of sweet-flavored. The young mice, which were 2 to 3 months old, were able to successfully adjust to their change in environment. Meanwhile, the older mice, which were 20 to 22 months old, became confused and were unable to distinguish between the levers in order to release the desired sweet-flavored pellets. This indicated to the team that the older mice may have been incapable of learning the new lever location of their favorite pellets due to brain aging. Was there a difference between the young and older mouse’s neural network?

“Elderly people often experience deterioration of these behaviors that can lead to fundamental problems in their everyday life, including the inability of being self-sufficient,” Bertran-Gonzalez told Medical Daily. “These results point out the importance of considering motivational decline in aged people, as it can potentially seed further complications such as cognitive decline and in some cases dementia.”

To find out, researchers examined each mouse using a technique called immunofluorescence analysis, which highlighted sections of their brain with a fluorescent microscope. They found deterioration in a specific circuit called the parafascicular-to-cholinergic interneuron pathway (PF-to-CIN), which is a circuit in the brain responsible for storing and processing new and existing information during goal-directed action. After locating the problem area, researchers tested it further by damaging the younger mice’s PF-to-CIN circuit and repeated the pellet lever tests. They found that young mice with damaged circuits acted just like the older mice.

“There is a brain circuit that appears to be especially sensitive to aging and that can lead to motivational decline,” Bertran-Gonzalez said. “It is important to detect the problem early on and design strategies to keep goal-directed action flexible, so that aged people can continue with their daily activities and enjoy a stimulating life for as long as possible.”

Bertran-Gonzalez and his team believe the PF-to-CIN circuit is an area of the brain that is often overlooked and that damages to it could be commonly mistaken for other age-related conditions among older people, such as poor memory and attention.

"We think that it is of utmost importance that motivational decline is considered as a condition in its own right, so that strategies can be efficiently implemented early on to prevent motivational problems in the aged," Bertran-Gonzalez said. "In addition to extending the quality of life in the elderly, efficient restoration of motivational behaviors could in some cases reduce the risk of further cognitive decline and progression to dementia."

Source: Bertran-Gonzalez J, Matamales M, Skrbis Z, Hatch RJ, Balleine BW, and Gotz J. Aging-Related Dysfunction of Striatal Cholinergic Interneurons Produces Conflict in Action Selection. Neuron . 2016.