If you’ve ever wondered why you procrastinate when it comes to doing your taxes early or getting started on mundane admin jobs at work, you’ll be pleased to know it’s not just because you dislike them. New research has uncovered a specific pathway in the brain that slams the brakes on investing energy in these tasks, making them harder to get done.
Researchers from Kyoto University’s Institute for the Advanced Study of Human Biology (WPI-ASHBi) set out to investigate “motivational paralysis,” which is nuanced and different for everyone but something that seems specifically shaped by our brain chemistry. It’s essentially an aversion to the harder or more “boring” executive-function tasks – something that anyone with neurodivergent brains will be painfully aware of. And with that paralysis and avoidance often come feelings of shame and guilt. But it’s more than just dopamine- and pleasure-seeking, it turns out.
In a study on macaque monkeys, the researchers uncovered what they best describe as a “motivation brake” – which is activated along the neural pathway that connects the ventral striatum (VS) and ventral pallidum (VP) regions of the brain. When that pathway interruption was disabled, blocking the brake effect, the animals’ resistance to unpleasant tasks was minimal.
“Classical reinforcement learning theories emphasize the role of goal valuation in motivating behavior, supported by findings that lowering expected value decreases the likelihood of associated actions,” the scientists explain in their study. “However, recent computational frameworks propose that the initiation of behavior may be regulated by mechanisms distinct from valuation, particularly under aversive contexts that impose additional costs, such as physical, cognitive, or temporal effort, on initiating behavior.”
The researchers set out a series of reward-based tasks for the monkeys, jobs designed designed to separate physical ability from motivation. In some trials, the animals had to invest more effort and experience some unpleasant experiences to get the reward at the end. However, the study wasn’t to see what the monkeys would do to seek the reward, but if starting the task wasn’t worth the payoff.
Taking this beyond observations of behavior, the researchers mapped the neural pathway connecting the VS and VP regions, identifying the neurons playing key roles in communication between the two zones. They then used electrophysiological recordings to monitor activity along this pathway while the monkeys undertook the behavioral tasks.
The monkeys were trained in two tasks – one that earned a water reward, and another that delivered the same prize but came with an unpleasant air puff direct to the face before reaching the goal. Before each task, the animals could see which path to follow, knowing what each entailed. And the researchers weren’t focused on which path the monkeys chose, but their hesitancy in approaching the less pleasant one. Because while the monkeys knew both paths led to a reward, one they were less eager to initiate.
Through this, the scientists found that the neural pathway circuit became more active when motivation dropped – in this case, when the animals were confronted with the more high-effort task. Essentially, the brain was pressing pause on exerting energy to deal with the job that was harder, regardless of the reward that was waiting at the end.
Biological function across species – from insects to humans – is a sort of supply and demand relationship when it comes to energy use. While we, as humans with advanced brains, are mostly unaware of this basic energy investment/payoff relationship – our neurons will still follow the path of least resistance. We, of course, can see that as laziness, or needing to work on motivation or try harder (many of these dictated by societal and environmental expectations), but this study shows there could be more biochemistry at play in our brains we’re coming up against.
“This chemogenetic study provides causal evidence that the VS-VP pathway regulates the initiation of goal-directed behavior under aversive conditions while exerting minimal effects on outcome valuation,” the researchers explain the study. “This dissociation supports computational models proposing that behavioral initiation and evaluative processes rely on distinct neural mechanisms. In particular, our findings suggest that aversive contexts can suppress initiation independently of value judgment, consistent with theories emphasizing the role of effort-cost computations in motivation.”
The study’s fascinating findings support the idea that the brain has dedicated neural systems that don’t just seek rewards and pleasure, but can work against behavior that perceives those tasks as being too emotionally or physically taxing. That distinction may prove important for understanding conditions like depression, attention-deficit/hyperactivity disorder (ADHD) and other neurodivergence – where intellectually understanding that there is a reward by completing harder tasks is overridden by the struggle to even start that to-do list.
“Our trial-history analysis further showed that modulation of initiation by the VS-VP pathway depended on recent error history rather than on goal valuation, suggesting that this pathway regulates motivation to initiate behavior in a history-dependent, context-specific manner,” the researchers confirm in the study. “The VS-VP pathway appears to be preferentially engaged in aversive contexts and to play a key role in sustaining task-driven motivation. Early in sessions, reward- and task-driven motivations likely act in parallel, but as reward-driven vigor declines with satiety, behavior becomes more dependent on task-driven motivation.
“These results highlight the VS-VP pathway as a critical substrate for regulating task engagement when goal pursuit conflicts with aversive outcomes,” they conclude.
The scientists also add some caution to their findings, as the pathway obstacles are, biologically speaking, there for a reason. So removing those guardrails may not be ideal, either.
“Over-weakening the motivation brake could lead to dangerous behavior or excessive risk-taking,” says Ken-ichi Amemori, lead author of the study. “Careful validation and ethical discussion will be necessary to determine how and when such interventions should be used.”
Nonetheless, the study is an important step towards understanding why we avoid some tasks in favor of others, regardless of the “reward” waiting at the end. In the future, interventions such as non-invasive brain stimulation, or new drugs, might help moderate this brake system, but it’s worth remembering that, biologically at least, this pathway obstacle exists to divert energy to where it’s most needed, and taking the proverbial foot off the pedal completely creates a deficit that isn’t likely to benefit us, either.
The study was published in Current Biology.
