When the brain listens to the body – 03/20/2023 – Suzana Herculano-Houzel

“State of mind” is a much nicer expression than “state of mind”, I agree – but the second is the scientifically correct option to describe how we feel in terms of disposition and motivation. After all, what we actually do depends not only on the orders the brain gives to the muscles to move, but also on what the brain judges to be worth the effort in the first place.

The interesting detail, however, is that two recently published studies show that the body, in addition to the brain, has quite a voice in what the brain agrees to do.

The first study, carried out at Harvard University, in the USA, began with one of those simple questions, which many thought had already been answered: why does an infection –flu or a common cold– leave us feeling down, lethargic, not wanting to do anything, not even eat? The word “inflammation” is certainly part of the answer, because anti-inflammatories like aspirin and ibuprofen help to improve that state of mind, in addition to relieving negative sensations in the body.

Hence the inflammation reaching the brain is another five hundred.

Using those genetic tools that require a lot of money and that Brazilian researchers generally only use when working abroad, the group led by Stephen Liberles, at Harvard, discovered that infection with the flu virus leaves mice lethargic and inappetent, just like us. , due to inflammation – but its effect on the brain does not pass through the blood, but through neurons that specifically represent the inflamed state of the throat and nasal passages.

If these neurons are silenced by genetic manipulation, animals with the flu remain alert and hungry. They are even much more likely to survive the flu, which shows that lethargy is not “adaptive” at all. Quite the contrary: you survive the flu despite your lack of appetite.

The second study, led by Karl Deisseroth, a scientist at Stanford University, also in the US, publicly quoted for the Nobel Prize, used the control of gene expression by laser, a trick invented by Deisseroth, to control not the brain of mice, but their heart. Question: would an experimentally induced tachycardia episode be capable of making animals anxious, as in cases of spontaneous tachycardia that arise in anxiety attacks?

The answer, very clearly, is yes – and because the brain, always the brain, detects the tachycardia it didn’t provoke and even so updates the body’s representation to include the new reality.

In absolutely innocuous contexts, tachycardia is just tachycardia, and nothing changes for the animal. But in naturally unsettling contexts, as high and open places are for mice (and lots of people), the tachycardia coming “out of nowhere,” that is, from the researchers’ laser aimed at the heart, is enough to make the animals visibly hesitant and anxious. .

Both studies agree: keeping a healthy mind when the body is not very healthy is difficult…

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