Japanese Study Explains How Dopamine Receptors Drive Motivation

Japanese Study Explains How Dopamine Receptors Drive Motivation

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If you’re feeling unmotivated, blame it on your dopamine receptors. A new study reveals that an impaired reward system can lead to disinterest in achieving life goals. Several neuropathological conditions, such as depression or anxiety, can lower motivation and diminish willpower.

In the latest Japanese study, scientists analyzed the behavior of monkeys after manipulating their reward system network. They found several vital missing components of their reward system which could explain their lack of motivation.

But, where does motivation come from, anyway? What drives us to achieve goals or complete monotonous tasks necessary for our survival? The answer lies in the reward system of our brains, which includes dopamine receptors. This evolutionary mechanism prompts us to work and helps us weigh the costs and benefits of taking risks. If we decide the perceived reward warrants the effort to earn it, this mechanism drives us to take that risk.

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However, their reward systems become weakened in people with neurological conditions like depression or Parkinson’s disease. This leads to decreased motivation to work, chronic fatigue, and blunted dopamine receptors.

This new information builds on previous research.

dopamine receptors
Previous studies have pointed to low dopamine levels as a core feature of disorders like depression. When the reward system becomes disrupted, it makes even simple tasks seem difficult to accomplish. The hallmark symptoms of depression such as lethargy or lack of motivation stem from disrupted dopamine receptors.

Recently, neuroscientists have begun studying how people can “beat the system” and overcome behavioral challenges. They’re investigating how the reward system performs cost-benefit analyses to decide whether to complete a task or not. By dissecting the brain’s dopamine receptors, they can figure out how to bypass learned behaviors and increase motivation.

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The Japanese study included Dr. Yukiko Hori of National Institutes for Quantum and Radiological Science and Technology, Japan, and her colleagues. Their research led to a greater understanding of how the reward system evaluates cost-benefit trade-offs. Their findings have been published in the journal PLoS Biology.

The study shows how dopamine receptors drive motivation.

Dr. Hori explains the purpose of their research: “Mental responses such as ‘feeling more costly and being too lazy to act’ are often a problem in patients with mental disorders such as depression, and the solution lies in the better understanding of what causes such responses. We wanted to look deeper into the mechanism of motivational disturbances in the brain.”

To perform the study, Dr. Hori and her colleagues honed in on dopamine (DA). This neurotransmitter encourages motivation and regulates behavior based on cost-benefit analyses. Dopamine gets transmitted in the brain through dopamine receptors or molecular anchors that bind DA molecules. These receptors send signals through neuronal pathways in the brain.

Since the receptors play specific parts in DA signal transmission, the scientists wanted to study how they influence DA signaling. So, using macaque monkeys as subjects, the team hoped to understand how the two classes of DA receptors affect motivation. These dopamine receptors are the D1-like receptor (D1R) and the D2-like receptor (D2R).

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In their research, the scientists first trained the animals to perform two different tasks: “reward size” and “work/delay tasks.” Then, the team measured how the required effort and perceived reward influenced behavior. They also altered the dopamine receptors of the monkeys to gauge their response.

Dr. Takafumi Minamimoto, the co-author of the study, explains the following:

“We systematically manipulated the D1R and D2R of these monkeys by injecting them with specific receptor-binding molecules that dampened their biological responses to DA signaling. By positron emission tomography-based imaging of the brains of the animals, the extent of bindings or blockades of the receptors was measured.”

Next, they allowed the monkeys to perform tasks to earn rewards. The team observed whether the monkeys accepted or refused to carry out the tasks. They also recorded their response time to cues related to the tasks.

Both classes of dopamine receptors play a critical role in making decisions

After analyzing the data, the scientists uncovered interesting findings of the dopamine receptors involved in decision-making. They found that the cost-benefit analysis of completing tasks required both D1R and D2R. What’s more, the team observed that these dopamine receptors played a role in two parts of the cost-benefit analysis:

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  • incentivizing the motivation (the size of the reward-motivated the monkeys to take action)
  • increasing delay discounting (the tendency to prefer immediate, smaller gratification rather than larger, delayed rewards)

They also noted that cost-benefit analyses involve DA transmission via both dopamine receptors. Specific neurobiological processes govern benefits or “reward availability” and costs or “energy expenditure associated with the task.” “Workload discounting,” the process of discounting the perceived value of rewards based on the effort required, only involved D2R manipulation.

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