Background
Most of us know the feeling: maybe it’s making a difficult phone call, starting a report you fear will be criticized, or preparing a presentation that makes you nervous just thinking about it. You understand what you need to do, but taking that first step is surprisingly difficult. When this difficulty becomes severe, it is medically known as a miscarriage. People with abulia aren’t lazy or ignorant: they know what to do, but their brain just can’t seem to hit the go button. Abortion commonly occurs in conditions such as depression, schizophrenia and Parkinson’s disease and severely disrupts a person’s ability to manage daily life and maintain social functions.
Research in neuroscience and psychology has suggested that before we act, the brain weighs how much effort a task might cost. If the cost is too high, motivation falls. But until now, it was unclear how the brain turns this judgment into a decision not to act. To explore this question, a research team at WPI-ASHBi applied an advanced genetic technique called chemogenetics to highly intelligent macaque monkeys, allowing them to temporarily and precisely adjust communication between specific brain regions and identify a circuit that acts as a brake on motivation.
Methods and key findings
Monkeys were trained to perform two types of tasks. In one, completing the task earned a water reward. In the other, the reward came with an added downside: an unpleasant breath of air in the face. Before each trial, the monkeys saw a cue and were free to decide whether to start or not. The researchers focused not on which option the monkeys chose, but on something more fundamental: did they take the first step at all? As expected, when the task involved only one reward, the monkeys usually started without hesitation. But when the task involved an unpleasant puff, they often held back, even though there was still a reward available.
The researchers then temporarily weakened a specific brain connection that connects two regions involved in motivation: the ventral striatum (VS) and the ventral pallidum (VP). In the reward-only task, suppression of this pathway had little effect on the monkeys’ behavior, and the monkeys started the task normally. By contrast, in tasks involving an unpleasant puff of air, the mental brake on starting was relaxed: the monkeys became much more willing to start. Importantly, the monkeys’ ability to judge rewards and punishments was not changed. What changed was the step between knowledge and action.
The researchers took a closer look at what was actually happening in these brain regions during this process. Neural activity in the VS increased during the stressful task, suggesting that it helps the brain register when a situation feels stressful. In contrast, activity in the VP gradually fell as the monkeys became less willing to initiate the task, indicating that these two regions play different roles. Together, these findings suggest that the VS to VP pathway acts as a “motivational brake” that suppresses the internal “go” button, particularly when faced with stressful or unpleasant tasks.
Future prospects
This discovery of the VS–VP “motivational brake” may shed light on conditions such as depression and schizophrenia, where severe loss of motivation is common. In the future, interventions such as deep brain stimulation, noninvasive brain stimulation, or new drug strategies may aim to fine-tune this brake when it becomes too tight. But this “brake” exists for a reason. While an overly tight brake can lead to a stall, a brake that is too loose could make stopping difficult, even in extremely stressful situations, potentially leading to burnout. In other words, the VS–VP circuit can help maintain motivation in a healthy range. “Too much weakening of the motivational brake could lead to risky behavior or excessive risk-taking,” said Ken-ichi Amemori, lead author of the study. “Careful validation and ethical debate will be needed to determine how and when such interventions should be used.”
In modern society, especially at a time when burnout is at an all-time high, these findings invite us to rethink what “motivation” really means. The brain can actively reduce the urge to act when tasks are unpleasant or stressful, so getting started isn’t just about willpower. Rather than trying to forcefully boost motivation, the focus should be on how society can better support people in dealing with stress. This is a question that requires wider social dialogue.
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