The study, led by neuroscientist Ken-ichi Amemori of Kyoto University, aimed to analyze the brain mechanisms that reduce motivation to perform a task when there is stress, punishment or discomfort. To do this, the researchers designed an experiment with monkeys, a widely used model for understanding decision-making and motivation processes in the brain.
The scientists worked with two macaques that were trained to perform various decision-making tasks. In the first phase of the experiment, after a period of water restriction, the animals could activate one of two levers that released different amounts of liquid; One option offered a small reward and the other a large reward. This exercise allowed them to evaluate how the value of a reward affects the willingness to perform a task.
At a later stage, an unpleasant element was incorporated into the experimental design. The monkeys were given the option of drinking a moderate amount of water without negative consequences or drinking a large amount of water under the condition of being subjected to a direct blast of air in the face. Although the second option had greater rewards, it involved an uncomfortable experience.
As the researchers predicted, the macaques’ motivation to complete the task and reach the water decreased significantly when the aversive stimulus was introduced. This behavior allowed them to identify a brain circuit that acts as a brake on motivation in the face of anticipated adverse situations. Specifically, connections were observed between the ventral striatum and ventral pallidum, two structures located in the basal ganglia of the brain, which are known for their role in regulating pleasure, motivation, and reward systems.
Neural analysis revealed that when the brain anticipates an unpleasant event or potential punishment, the ventral striatum becomes activated and sends an inhibitory signal to the ventral pallidum, which is normally responsible for driving the intention to perform an action. In other words, when the task is associated with a negative experience, this communication reduces the impulse to perform the task.
The brain connection behind procrastination
To investigate the specific role of this connection, as described in the study published in the journal Current Biology, the researchers used a chemogenetic technique that, through the administration of a particular drug, temporarily disrupted communication between two brain regions. By doing this, the monkeys regained the motivation to begin the task, even in trials that involved blowing air.
Specifically, the inhibitory substance made no changes in trials where punishment was not accompanied by reward. This result suggests that the EV-PV circuit does not regulate motivation in a general way, but is activated specifically to suppress it when discomfort is expected. In this sense, as communication between these two areas intensifies, indifference to unpleasant actions appears to gradually develop.
In addition to explaining why people unconsciously undertake household chores or resist inconvenient obligations, the findings have relevant implications for understanding disorders such as depression or schizophrenia, in which patients often experience significant impairment in the desire to perform tasks.
However, Amemori emphasizes that this circuit performs an essential protective function. “Overwork is very dangerous. This circuit protects us from burnout,” he said in comments reported by Nature. Therefore, he cautions that any attempts to externally modify this nervous system should be done with caution, as more research is needed to avoid interfering with the brain’s natural protective processes.
This story originally appeared in WIRED en Español and is translated from Spanish.
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