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CHICAGO (Xinhua) – A study from Northwestern University (NU) has uncovered some of the most obvious evidence that animals can judge time.
By examining the medial entorhinal cortex of the brain, the researchers discovered a hitherto unknown set of neurons, which lights up like a clock when an animal is waiting.
NU researchers have set up an experiment called a "door stop" virtual task.
In the experiment, a mouse turns on a physical treadmill in a virtual reality environment.
The mouse learns to go down a hallway to a door halfway down the track. After six seconds, the door opens, allowing the mouse to continue down the hall to receive its reward.
After several training sessions, the researchers made the door invisible on the virtual reality scene.
In the new scenario, the mouse always knew where the now invisible
"Door" was located according to the changing textures of the floor. And he waited six more seconds at the "door" before running abruptly on the track to recover his reward.
"The important point here is that the mouse does not know when the door is open or closed because it's invisible," said James Heys, a postdoctoral fellow at NU and first author of the study.
"The only way for him to effectively solve this task is to use the sense of internal time in his brain."
The UN researchers pushed the experiment even further by analyzing the brain activity of the mouse.
Using two-photon microscopy, which allows advanced imaging of the brain at high resolution, they observed the fire of mouse neurons.
"As the animals run along the track and head for the invisible gate, we see the cells firing that control the spatial encoding," said Daniel Dombeck, associate professor of neurobiology at
College of Arts and Sciences, Weinberg (NU).
"Then, when the animal stops at the door, we see these cells go out and a new set of cells light up.
It was a big surprise and a new discovery.
"Not only are the cells active during rest," he said, "but they actually encode how long the animal is at rest."
The researchers discovered these new time-coded neurons. They can now study the incidence of neurodegenerative diseases on this set of cells.
"Patients with Alzheimer's disease forget that events happen on time," said Heys.
"It may be because they lose some of the basic functions of the entorhinal cortex, one of the first areas of the brain affected by the disease.
"This could therefore lead to new tests for early detection of Alzheimer's disease," added Dombeck.
"We could start asking people to judge the elapsed time or ask them to navigate a virtual reality environment – essentially asking a human to do a" door stop "task."
The study was published online in the journal Nature Neuroscience journal.
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