What makes the brain keep chasing a reward when the effort starts to outweigh the payoff? A small group of cells may help decide when to persist and when to give up.
Researchers at Nagoya University in Japan found that orexin neurons became increasingly active as rats worked harder to obtain food. Silencing the cells weakened the animals’ willingness to continue, suggesting that the orexin system helps convert the expectation of a reward into persistent action.
The findings, published in Proceedings of the National Academy of Sciences of the United States of America (PNAS), offer a new view of a brain system best known for controlling wakefulness.
More Than a Wakefulness Signal
Orexin neurons are found in the hypothalamus, a region deep in the brain that helps regulate sleep, hunger, energy balance, and other basic functions. Although relatively few in number, these neurons send signals across much of the brain and can influence arousal, reward processing, and behavior. Orexin is also called hypocretin.
The system has a well-established connection to sleep. The loss of orexin-producing neurons is closely associated with narcolepsy, a disorder that can cause severe daytime sleepiness and sudden muscle weakness. Orexin was originally linked to appetite, but scientists increasingly view it as a broader coordinator of wakefulness, energy needs, and actions that support survival.
That combination makes orexin a plausible link between being alert and having a reason to act. Staying awake is not enough to achieve a difficult goal. The brain must also decide that the expected payoff remains worth the cost.
The Nagoya University team, led by Associate Professor Hiroyuki Mizoguchi and Professor Emeritus Kiyofumi Yamada of the university’s Graduate School of Medicine, set out to determine whether orexin neurons help make that calculation.
Measuring the Willingness to Keep Trying
The researchers created genetically modified “orexin-Cre” rats that allowed them to target orexin-producing neurons with unusual precision. Rats were selected because their strong learning abilities make them well suited for demanding behavioral experiments, although manipulating specific groups of neurons in rats has historically been more difficult than in mice.
The animals completed a progressive ratio test, a standard experiment used to measure how much effort an animal will invest in obtaining a reward. The rats had to make repeated touches to earn food, and the number required increased after each successful trial.
Eventually, the effort became too great and the animal stopped. This stopping point (the breakpoint) provided a measure of how strongly the rat was motivated to continue.
When the researchers activated orexin neurons using chemogenetics, the rats reached higher breakpoints and completed more work for the food. Rats in which orexin neurons had been selectively damaged quit sooner.
The result indicated that the cells were not merely responding to movement or food consumption. Their condition appeared to influence how long the animals were prepared to work.
Orexin Activity Rose With the Cost of the Reward
The scientists next used fiber photometry to track orexin neuron activity as the rats performed the task.
The cells became more active while the animals anticipated a reward, then quieted after the food arrived. When an expected reward did not appear, activity remained elevated.
The response also grew stronger as earning the food required more effort. In other words, orexin neurons appeared to track not only the possibility of a reward, but also the rising cost of obtaining it.
This pattern suggests that the cells may help maintain goal-directed behavior during the period between expecting a result and achieving it. Rather than simply producing pleasure, orexin may support the state of arousal and persistence needed to keep working while success is still uncertain.
Silencing Orexin Neurons Reduced the Drive to Persist
To test whether orexin activity directly caused the behavioral changes, the team used optogenetics, a technique that controls selected neurons with light.
Suppressing orexin neurons while the rats anticipated a reward produced a clear effect. The animals took longer to complete effort-based tasks and stopped at lower breakpoints.
The opposite experiment produced a more complicated result. Artificially stimulating the cells successfully increased their activity, but the rats did not work harder than they normally would.
Orexin May Set the Foundation for Motivation
This imbalance is important. It suggests that orexin neurons are necessary for maintaining motivation, but that motivation cannot be increased indefinitely by pushing those neurons beyond their natural activity.
Without sufficient orexin signaling, persistent behavior breaks down. Once the necessary signal is present, however, other brain systems may determine how much additional effort an animal is willing to make.
Factors such as reward value, hunger, past experience, stress, and competing goals could all influence that decision. The timing and pattern of orexin activity may also matter more than its overall intensity.
“Our study demonstrated significant changes in orexin neuron activity depending on expected rewards and the effort required, suggesting a potential mechanism for translating expectations into sustained action,” Mizoguchi concluded.
The team plans to study the signals entering and leaving these neurons. Mapping those connections could reveal how the brain decides that a goal remains worth pursuing, even as the work required to reach it continues to grow.
Reference: “Reward prediction is encoded by orexin neuron activity during motivated behavior” by Yutao Dong, Sheikh Mizanur Rahaman, Wenjun Zhu, Ayumu Inutsuka, Daisuke Ono, Rinako Tanaka, Tetsuo Matsuzaki, Eiji Shibata, Madoka Isobe, Shuntaro Izawa, Akihiro Yamanaka, Kiyofumi Yamada and Hiroyuki Mizoguchi, 29 June 2026, Proceedings of the National Academy of Sciences.
DOI: 10.1073/pnas.2520677123
This work was supported by Grant-in-Aid for Scientific Research [22K19749; 23K27360; and 23H02669 (2023)]; SENSHIN Medical Research Foundation; Naito Foundation, Japan; Takeda Science Foundation, Japan; SRF, Japan; Asahi Glass Foundation, Japan; Mishima Kaiun Memorial Foundation, Japan; Kao Health Science Foundation, Japan; and AMED, Japan (JP21wm0425014).
Never miss a breakthrough: Join the SciTechDaily newsletter.
Follow us on Google and Google News.