Animals can track the passing of time, science says

Preparing your dog’s dinner in the kitchen, you get a text message. You stop, sit down, and type out a response. “Fido won’t mind waiting a minute,” you say to yourself as he watches from his empty bowl.

Science says that, actually, Fido might mind.

Researchers from Illinois’s Northwestern University looked at the medial entorhinal cortex — a part of the brain associated with memory, navigation and keeping track of time — in animals. They found a previously unknown set of nerve cells, or neurons, that activate when an animal is waiting.

“Does your dog know that it took you twice as long to get its food as it took yesterday? There wasn’t a good answer for that before,” said study lead Daniel Dombeck. “This is one of the most convincing experiments that animals really do have an explicit representation of time in their brains when they are challenged to measure a time interval.”

Because of the medial entorhinal cortex’s ability to encode spatial information into “episodes,” or memories, Dombeck theorized that this part of the brain could also be involved with encoding an animal’s perception of time in a similar way.

“Every memory is a bit different,” said researcher James Heys. “But there are two central features to all episodic memories: space and time. They always happen in a particular environment and are always structured in time.”

An elaborate, virtual reality (VR) mouse maze was used to test the hypothesis. In the real world, a real mouse would run on a real treadmill while experiencing a VR hallway closed off by a VR door. Upon reaching the door in VR, the mouse would face a six-second wait, then the door would silently open, revealing a prize at the end of the hallway.

After a few rounds of this, the door was made invisible in the VR simulation. The mouse could still identify where the door was thanks to a change in the floor texture, but the door itself couldn’t be seen. But even then, the mouse would stop at the door and wait — precisely six seconds — before continuing to the reward beyond.

“The important point here is that the mouse doesn’t know when the door is open or closed because it’s invisible,” said Heys. The VR environment meant no other sensory cues could tip the mouse off about the door’s open or closed state. “The only way he can solve this task efficiently is by using his brain’s internal sense of time.”

There’s more to it than that, though. An imaging technique called two-photon microscopy let the researchers see each mouse’s brain activity.

“As the animals run along the track and get to the invisible door, we see the cells firing that control spatial encoding,” Dombeck said. “Then, when the animal stops at the door, we see those cells turned off and a new set of cells turn on. This was a big surprise and a new discovery.”

And while it’s always great to better understand our animal friends, it’s a bonus when the research can be used to promote human health as well. The researchers hope their findings can be used to learn more about Alzheimer’s, perhaps to design new early-detection tests.

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