Researchers Uncover Brain Circuit Behind Motivation Killer

Handling customer complaints or tackling summer homework — tasks you know you must do, yet can't quite bring yourself to start. This familiar hesitation, often dubbed the "motivation brake," is something almost everyone has experienced. 

Now, for the first time in primates, a research team from Kyoto University and other institutions has identified the brain circuits and mechanisms underlying this phenomenon through experiments with Japanese macaques.

In addition to advancing treatment prospects for depression, the research may have implications for burnout syndrome, a condition characterized by prolonged overexertion followed by an abrupt collapse in motivation.

The Science of Motivation Loss

Even when an action is clearly necessary, anticipated failure or negative evaluation can undermine motivation, a phenomenon frequently encountered in daily life. 

In its severe form, the condition is clinically referred to as "decreased spontaneous motivation" and is linked with substantial impairment in social functioning, especially among patients with depression or schizophrenia.

Behavioral science and neuroscience have suggested that, before an individual initiates an action, the brain evaluates the anticipated effort cost and determines whether to proceed. 

Until now, though, the neural mechanisms underlying this process had not been fully elucidated.

To investigate this question, a research team led by Associate Professor Kenichi Amemori of Kyoto University's Institute for the Advanced Study of Human Biology (ASHBi) conducted experiments on two highly intelligent Japanese macaques to identify the neural circuits involved and clarify their function.

Switching Off Motivation Loss

In the experiment, the macaques were presented with two types of tasks: an easy task that offered a water reward, and an aversive task that combined the same reward with a penalty in the form of air blown toward their faces. 

Upon seeing a signal appear on a screen, the subjects decided whether to initiate the task.

The experiment showed that the macaques were less motivated, taking longer to begin tasks that paired a reward with an unpleasant stimulus.

The team then employed chemogenetics to suppress the neural circuit linking the ventral striatum (VS) and ventral pallidum (VP) and conducted the same experiment. 

While no behavioral changes were observed during the easy task, the two macaques initiated the unpleasant task without hesitation.

According to the team, the VS–VP pathway functions as a "motivation brake," suppressing motivational drive under conditions of high stress. The results were published in the online edition of an American academic journal.

Implications for Mental Health

Previous research had identified the ventral pallidum as a key region involved in controlling motivation for action, often described as a "motivation switch." 

However, this study is the first to show that the pathway can also function as a brake.

"Both excessively high motivation and excessively low motivation can affect the mind and body," Amemori said. "The brain likely possesses a braking function to protect itself."

He added that viewing motivation through the lens of regulating this braking function could provide a foundation for understanding disorders such as depression and schizophrenia, and eventually for developing treatments. Both conditions involve marked declines in spontaneous motivation, as does burnout syndrome.

Based on the findings, Amemori said his team plans to explore less burdensome treatment approaches, such as ultrasound-based brain stimulation. "We hope this will spark broader societal discussion about the relationship between stress and motivation."

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Author: The Sankei Shimbun

(Read this in Japanese)