We don’t know what a mouse dreams about. Why He Might Be Dreaming – New Scientist

Do animals dream? And if so, what do they dream about? And why? Research showing that mice in their dreams look closely around them brings us one step closer to the answer.

I come from my nest, from the warm protection of my hole. The sun shines. Do I smell something there? Food? A cat? I take a good look around. Left right. No, nothing to see, I dare to go on, but take a good look around me.

Of course, we don’t know, but maybe mouse dreams look something like this. In any case, this scenario would fit well with an experiment that neuroscientists Yuta Senzai and Massimo Scanziani of the University of California San Francisco conducted on sleeping mice.

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We know that animals – mice, but also humans – have different types of sleep. There is deep sleep, in which brain waves show a calm, predictable pattern, and REM sleep, in which the brain waves are similar to those in the waking state. The eyes also make darting movements back and forth, the so-called rapid eye movements (brake).

Scan hypothesis

When people are awakened during REM sleep, they often report that they were just dreaming. But what do those eye movements mean? Do they correspond to the gaze that wanders over the dream landscape, the so-called scanning hypothesis? Or are they just random?

‘Other muscle movements are turned off during sleep, the eye muscles are an exception,’ says neuroscientist Chris de Zeeuw from the Netherlands Brain Institute in Amsterdam. Therefore, eye movements give an insight into the dream world.

De Zeeuw and his colleague Cathrin Canto are also involved in dream research. They wrote a comment on the article by Senzai and Scanziani in the trade journal science.

The scanning hypothesis is surprisingly difficult to prove, says Canto. “You can wake someone up during REM sleep and ask about the dream, but that research has produced mixed results.”

Compass type

You certainly can’t ask a mouse what he dreamed (at least: you won’t get an answer). Therefore, the American researchers took a different tack. It is known that certain brain cells keep track of the position of the head: these head direction cells (HD) act as a kind of compass. For example, one particular cell only becomes active when the head is turned 30 degrees in space.

The researchers applied electrodes to the mice to measure the activity of HS cells. They also constructed an ingenious structure on the mouse’s head, with an infrared LED light, mirrors and mini-cameras, so that they could continuously measure the movements of the mice’s eyes.

A clear pattern can be seen in awake mice: when the animal turns its head, its eyes often turn in the same direction to follow an object.

Practice movements

The same thing, the researchers discovered, happens during REM sleep. “The eyes turned in the same direction as the HD cells indicated, even though the mouse’s head doesn’t really move during sleep, of course,” says Canto. Apparently, the eyes of the mouse are looking around the dreamed landscape.

And that, in turn, could shed more light on the function of dreams. Dreams are known to help retain memories. De Zeeuw: ‘If you keep waking people up during their REM sleep, they will remember the learned facts less well.’ He and Canto published research suggesting that this also applies to motor memories: movements rather than facts.

“Movements correspond to certain circuits of brain activity that you can help sharpen by playing them more often,” explains De Zeeuw. For example, athletes can train without getting off the couch by visualizing how to perform a certain movement. “Perhaps dreams serve to practice movements without actually performing them,” says De Zeeuw. Including movements of the head and eyes.

Research like Senzai and Scanziani brings the understanding of dreams, memory, learning and sleep one step closer. “It’s fascinating research,” says de Zeeuw. “This means that for the first time we can objectively measure what happens in a dream.” Even if it’s a pipe dream.

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