Opinion – Suzana Herculano-Houzel: Another sleep mystery deciphered

More than twenty-four thousand neuroscientists from various countries are this week at the annual meeting in the US, trading cards, and will return to their respective laboratories full of new information and ideas.

I exceptionally stayed home because my parents were coming for my 50th birthday, although the US Consulate smeared my plans by denying my mother a visa — proof that having a green card in this country doesn’t make the family welcome, but that’s another story. I’ve also traveled enough this year, so while my colleagues exchange stickers in person, I review the literature.

I found in my pile of promising topics an article in Science magazine from August that kills a 70-year-old riddle: where do rapid eye movements in dreams come from? Are they random, or do they correspond to eye and head movements in what you are dreaming about?

Yuta Senzai and Massimo Scanziani of the University of California, San Francisco, respond. The two took advantage of the fact that it is possible to record, with electrodes implanted in the brains of mice, the activity of neurons in the thalamus that represent the current direction of the head in the horizontal plane, while monitoring eye movements, all In real time.

While the animal is awake and exploring the environment, eye and head movements are perfectly matched: the second immediately follows the first —exactly as in Daniel Filho’s tip to Regina Duarte, teaching her to raise her eyes before lifting her head in front of the camera (the trick obviously impressed me, I was a girl and I remember!).

The logic: the eyes automatically move towards what you see moving; the head follows—and a very cool reflex that envelops the labyrinth, in the inner ear, slides the eyes back to the center of the orbit when facing the new target head-on.

And when the animal falls asleep and begins to dream… Senzai and Scanziani discovered that the eye movements, which keep happening, precisely precede a new virtual direction of the head, signaled by the thalamus.

The simplest explanation for the phenomenon is that the content of dreams — images, sounds, touches, and also inner planes represented by the brain — causes eye movements, which virtually “move” the dreaming head.

But while dreaming, the head and the rest of the body, paralyzed, don’t really move, so it won’t be that reflection of the labyrinth that will bring the gaze back to the center. No problem: perhaps caused by the virtual movement of the head, caused and represented by the brain, the eyes soon move in the opposite direction in the same way.

What the mice were dreaming about, we still don’t know. But the new finding seems to me a very strong indication that the eyes do move as we mentally enact our dreams.

Hmmm. All the more reason to sleep with my blindfold on…