Do nonhuman animals live in a kind of eternal present, or are they aware of the passage of time? That question has been debated by scientists for decades.
Most experts agree that animals have some way of measuring time, but how their brains process time has long been a mystery. We may never know what the passage of time feels like to other animals, but researchers are beginning to discover what’s going on in the brain when animals process time.
How Animals Process Time
Daniel Dombeck, a neuroscientist at Northwestern University, has done a lot of work on what happens in the brain as it forms, stores, and recalls memories. As you might imagine, this kind of work often involves mice and mazes. However, in Dombeck’s lab, they let the mice play video games — that is, they use a virtual reality maze. This turned out to be a brilliant way of designing an experiment to study how animals process time.
The researchers knew that spatial navigation and episodic memories are encoded in the temporal lobe, specifically in the medial entorhinal cortex (MEC). Episodic memory is the memory of specific events: what you did last Tuesday, what you had for breakfast, what you were doing the last time you saw your keys.
So they thought that perhaps that area of the brain could also be involved in encoding time. To test the idea, they trained mice to run on a treadmill in a virtual reality environment. About halfway down the track, the mice came to a closed door. After six seconds, the door opened; a click signaled the start of the countdown. The mice continued through the door to get their reward. If the mice tried to run before the six seconds had expired, it was game over. No reward.
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Encoding Time in the Brain
Then the scientists changed the game. They made the door invisible. The mice could still tell where the door was, because the floor of the track changed. But the mice could not tell, by vision, hearing, smell, or any other cue, if the door was open. The only way they could tell when the door opened was by knowing that those six seconds had elapsed. And for that, they needed to rely on an internal sense of time.
Meanwhile, the researchers monitored activity in the animals’ brains. They found a group of neurons that appeared to encode time. While the mice were running along the track, brain cells that control spatial encoding were firing. When the mice stopped at the invisible door, those cells stopped firing, and a set of cells the researchers called ‘timing cells’ turned on. These cells encoded how long the animal rested in front of the door.
“People knew that animals had an estimate of time, but it wasn't known where that representation of time came from in the brain,” says Dombeck. “Our work was one of the first to pinpoint this specific part of the brain, the medial temporal lobe, as a place where the time cells might actually sit, and where the sense of time might arise.”
Dombeck adds that the idea of exactly where in the brain time is processed is still controversial. Time representations have been found in the striatum and the lateral cortex as well. However, in a follow-up study, Dombeck and colleagues silenced the MEC while the mice were learning the task. And sure enough, the mice couldn’t perform the invisible door task.
Still, there is much work to be done to understand how the brain processes time.
“Figuring out how all of these different timing circuits interact with each other and how the brain chooses which one to pay attention to at any given moment is where a lot of the work is going in the future,” Dombeck says.
Time Moves Slow and Fast
Dombeck also points out that other animals don’t experience time the way we do.
“They don’t have clocks; they’re not counting seconds,” he says. “It’s not clear what time means to them.” And, of course, they can’t tell us.
However, one thing we do know is that time doesn’t pass the same way for all animals. According to research by Kevin Healy and others, small animals with faster metabolisms, birds, for example, process more information in a given amount of time — visually, they process more frames per second — than do larger animals.
That’s why it’s so difficult for a human to catch a fly. The fly has more opportunity to see what you’re doing than you have to see what it’s doing.
This difference in processing speed means these animals experience time more slowly. On the other hand, large animals with slower metabolisms, such as giant turtles, experience time faster.
In more recent work, Healy has shown that dragonflies can process 300 changes per second. Humans can manage only about 65 changes per second.
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Article Sources
Our writers at Discovermagazine.com use peer-reviewed studies and high-quality sources for our articles, and our editors review for scientific accuracy and editorial standards. Review the sources used below for this article:
Nature Neuroscience. Evidence for a subcircuit in medial entorhinal cortex representing elapsed time during immobility
Cell. Inactivation of the Medial Entorhinal Cortex Selectively Disrupts Learning of Interval Timing
Animal Behaviour. Metabolic rate and body size are linked with perception of temporal information
Science Direct. Critical Flicker Fusion
British Ecological Society. Research reveals which animals perceive time the fastest
Avery Hurt is a freelance science journalist. In addition to writing for Discover, she writes regularly for a variety of outlets, both print and online, including National Geographic, Science News Explores, Medscape, and WebMD. She’s the author of Bullet With Your Name on It: What You Will Probably Die From and What You Can Do About It, Clerisy Press 2007, as well as several books for young readers. Avery got her start in journalism while attending university, writing for the school newspaper and editing the student non-fiction magazine. Though she writes about all areas of science, she is particularly interested in neuroscience, the science of consciousness, and AI–interests she developed while earning a degree in philosophy.
