Now, researchers have discovered the reason behind it—and it may have implications for the future of antidepressants.

Researchers from Northwestern University in Chicago deprived mice of sleep for a short period of time, then observed their behaviors and brain activity. They found that the mice’s brains released more dopamine—a neurotransmitter and hormone involved in pleasure—during sleep loss. 

What’s more, they discovered that the mice’s brains re-wired themselves, with neurons in the brain’s prefrontal cortex forming synapses to receive the dopamine. The findings could help researchers understand how mood transitions naturally occur and how fast-acting antidepressants like ketamine work, researchers say. Their findings were published Thursday in the journal Neuron.

“Surprisingly, our findings reveal that even a brief period of sleep loss can exert a more substantial impact on our brain function than we had initially anticipated,” Yevgenia Kozorovitskiy, an associate professor of neurobiology at Northwestern University and a co-author of the paper, tells Fortune. “This is an important reminder of how our casual activities, such as a sleepless night, can fundamentally alter the brain in as little as a few hours.”

The antidepressant effect of sleep loss in some mice mirrors the way ketamine works, she says. Ketamine also promotes the formation of synapses to receive dopamine in the prefrontal cortex. That’s why its antidepressant effects can endure for days, even though the medication leaves the body quickly.

Not all neurons are the same

Not all mice behave the same after brief sleep deprivation, just as not everyone responds the same to antidepressants, Kozorovitskiy says. For instance, mice that tended to be aggressive or hypersexual before sleep deprivation were more so with sleep deprivation. 

That’s because different brains have different dopamine pathways. And as scientists are learning, not all dopamine neurons function the same way, with their location in the brain apparently making a difference.

“Dopamine neurons play very important but very different roles in the brain,” she says. Unlike researchers once thought, “they are not just this monolithic population that simply predicts rewards.”

Knowledge gained from this study could help scientists create new antidepressants that target the prefrontal cortex, researchers say. 

Don’t try this at home

In the meantime, scientists emphasize that they’re not recommending that anyone pull an all-nighter in an effort to improve their low mood. It doesn’t work for everyone. Furthermore, chronic sleep deficiency, especially, has been linked with increased anxiety and mental distress, poor decision-making, and accidents.

“The antidepressant effect is transient, and we know the importance of a good night’s sleep,” Kozorovitskiy says. “I would say you are better off hitting the gym or going for a nice walk.”