In 2015, when cognitive neuroscientist Devin Terhune was hit by a car, the impact took less than a second, but he felt it to be much longer.

“I was riding [my bike] very fast, and so when I hit the car I went flying back around 15 feet or more,” he says. “Objectively, I'm sure the whole thing probably unfolded in less than a second but I experienced flying through the air as lasting at least 5 seconds—it felt very slow.”

Time stretched out from milliseconds to seconds and Terhune lived first-hand something we experience in less dramatic ways each day. We measure time in set amounts— seconds, minutes, and hours. But the way time feels is more slippery. Ten minutes while you’re bored is an eternity and those same ten minutes with your best friend disappear like nothing.

This flexibility in perceiving time is only enhanced when psychedelic drugs enter the mix. A review from 1964 on hallucinogens reveals how long we’ve been playing with the dials of time—speeding it up, and slowing it down—through drugs. One account from 1913 on mescaline intoxication said that mescaline made a person feel like “the immediate future was rushing on at chaotic speed, and the time was boundless.”

A study from 1954 found time disorders in 13 out of 23 people under the influence of psychedelics. Most of them felt a "sense of temporal insularity,” where only the present was real and the past and future were far, far away. “One subject experienced a 'timeless, suspended state; a few felt time to be slipping away very quickly, whilst in others the passage of time was slowed down,” the review wrote. “In one case where the mood fluctuated between elation and depression, the passage of time was experienced concurrently as rapid and slow.”

The perception of time is a fundamental process of the brain, linked tightly to attention, emotions, memory, psychiatric and neurological disorders, and even consciousness—but while scientists have been anecdotally noting how drugs can change time perception for decades, very few have been able to address the question rigorously with tightly designed studies.

Terhune says he’s been interested in understanding the neurochemical mechanisms involved in the distortions in the perception of time, and these drugs are one way to do that. Psychedelics act on specific pathways and chemicals in the brain, and if they also change the perception of time, we could learn exactly how it happens.

At the end of November, Terhune and his co-authors published a randomized, double-blind, placebo-controlled study in Psychopharmacology on the effects of microdoses of LSD on people’s perception of time. They found that even at small doses, LSD seems to change the way people interpret time, though the specifics of how and when are still to be determined.

In the new work, 48 healthy people were split up into four groups. One group got a placebo, and the other three received different small doses of LSD: 5, 10, or 20 micrograms. Then, they did what’s called a temporal reproduction task. In this task, you see something on a screen for a certain amount of time—in the study it was a blue circle—and are asked to remember and recreate how long you saw it.

The participants were shown a blue circle for periods of time from 800 milliseconds all the way up to 4,000 milliseconds, in increments of 400 milliseconds. “So, this blue circle would appear on the screen for, say, 1,200 milliseconds, or 1,600 milliseconds, whatever it might be,” Terhune says. “The participant had to focus on that, estimate and memorize that duration.” They would then hold the space bar down on the computer for the same amount of time they saw the circle.

Terhune and his colleagues looked to see how accurate the different groups of people were in reproducing those intervals, and found that the people in the LSD groups tended to hold down the space bar for significantly longer periods of time than the placebo condition. The researchers call this “over-reproduction.”

Importantly, Terhune says that they saw these changes in time perception without any major conscious effects from the drug. They asked people to report if they felt anything from taking the LSD, like perceptual distortions, unusual thoughts, if they felt high, or if it affected their concentration. There were a couple of weak effects, but statistically, the change in time perception happened independent of any subjective influence of the drug.

In previous work on time perception and hallucinogens, a factor that complicated interpretation were the strong effects from the drugs themselves. When time perception changed for people in those studies, was it truly because their perception had changed, or was it rather that their attention had shifted, for instance, to a strange visual hallucination across the room?

Still, it can be a little complicated to unpack what the findings really mean. Terhune says that it could be that people saw the blue circle on the screen, they perceived it to last longer than it did, and that’s why they held the space bar down longer. Or was time perception affected at a different point—for instance, when they were holding down the space bar?

Manoj Doss, a postdoctoral cognitive neuropsychopharmacologist at Johns Hopkins University who studies memory, tells me there could be an issue with encoding. In a Twitter thread about the paper, he explained what he means by that: “Let's pretend you thought to yourself that an initial interval felt like 3 seconds (and it actually was). When you're reproducing it under a state in which time feels twice as long, you would think that 3 seconds passed when actually only 1.5 seconds had passed. This means that participants in their study could have encoded the interval in a perfectly normal fashion but felt that time had "sped" up during the reproduction interval, thereby leading to longer estimation. My guess is that both effects are at play.”

“These things are a bit difficult to tease apart,” Terhune agrees. “In this study, we certainly were not able to do that, so we definitely want to be kind of cautious.”

But the main finding of over-reproduction is intriguing despite what’s exactly causing it. In the few other studies using psychedelics and this exact task, the opposite has been found. Marc Wittmann is a neuropsychologist at the Institute for Frontier Areas of Psychology and Mental Health in Germany, the author of a recent book Altered States of Consciousness: Experiences Out of Time and Self, and one of the leading figures in the field of time perception and altered states. He has co-authored nearly all of the other papers on psychedelics and time perception, and found that when people were given psychedelics, they under-reported intervals—the converse of Terhune’s findings.

“I was a little surprised concerning the over-reproduction, but it's actually very interesting,” Wittmann tells me. “In our former studies, also with microdoses of psilocybin [the psychoactive compound found in magic mushrooms], which is a slightly different drug but also psychedelic and very, very similar to LSD, we found an under-reproduction,”—meaning that when people reproduced the duration they had seen, they did for less time it had actually been.

In 2007, Wittmann and colleagues tested 12 healthy people on medium and high doses of psilocybin and found that psilocybin significantly impaired their ability to accurately reproduce intervals longer than 2.5 seconds. In a 2008 paper in Neuroscience Letters, co-authored with University of Zurich’s Franz Vollenweider, psilocybin also shortened people’s reproductions of intervals. In that study, there was an experiment where the people were given a low dose.

The comparison of Terhune's work to the experiment with a low dose of psilocybin is especially exciting, says Doss. "If you have two drugs that essentially do very similar things in the brain and one is doing the opposite, has the complete opposite effect, that's amazing," he says.

Terhune doesn’t see his results as contradicting Wittmann’s necessarily, it just means we have more to learn. Wittmann speculated that LSD could have a more varied response in the brain than psilocybin does. Psilocybin mainly affects the serotonin system. LSD affects serotonin, but also the dopamine system, and might be one reason Terhune had different results.

Terhune says there is some intriguing work in animals that hints at the possibility that LSD might act in stages in the brain: first on serotonin, and then later, on dopamine. Since his participants were tested about two hours after they were dosed, that could explain why their time perception was different. But since no human studies have looked at this yet, it remains just a hypothesis for now.

If we understood exactly how time perception works, could we modulate it for our benefit? People with depression and other psychiatric or neurological disorders have expressed differences in the perception of time. Might intentionally accelerating or decelerating time help with any of these disorders? In depression, time seems to slow down or stop altogether.

“This is very much related to very strong emotions, negative emotions, and there's this feeling of being stuck in time,” Wittmann says.

At the moment, there isn't one unifying theory on how regular time perception works, Wittmann tells me. He thinks that subjective time is very closely related to the body and how much we feel our bodies—something called interoception—and that a brain area responsible for sensing our internal body signals might also be responsible for feeling the passage of time.

Further work in LSD and psilocybin, with attention paid to timing and dosage, could reveal these subtleties even further and show not just how time perception changes while on drugs, but how it works in everyday life, and perhaps a bigger question underneath.

And for Wittmann, understanding the perception of time is inextricably linked with an understanding of one of life’s greatest mysteries: consciousness. Terhune agrees that there's a very close link between our conscious experience and our perception of time.

“I would say time consciousness and self-consciousness are modulated together,” Wittmann tells me. “If you're bored, what happens? You're very much related to your self. You're very self-reflective. You feel yourself and your bodily self very much, and time drags. But if you are some sort of less aware of yourself, because you're in an interesting conversation, you're watching a movie or something, or you're doing sports or something, you're in this flow mode, then you don't notice yourself very much, your bodily self, and time passes very quickly. There, you see how perception of self and time are totally interrelated.”