Opinion – Suzana Herculano-Houzel: The brain economy is limited by the local supply

It is not new that wars are fought with economic sieges. The difference is that physical sieges, which prevented besieged populations from leaving their cities to bring food and other resources, are now joined by restrictions on the passage of intangible financial resources. But the principle is the same: the functioning of complex living systems depends on flows of energy and matter, and stopping these flows is a guaranteed way to extinguish complexity first, and then life.

I was telling you last week that my colleague Douglas Rothman and I at Yale University recently demonstrated that the brain’s economy is also limited by the flow of energy and matter, in the form of the blood circulation that supplies neurons and the glial cells that accompany them with oxygen. and nutrients. Until then, our colleagues assumed that cerebral blood circulation was abundant enough to not be limiting. Just as muscles that are in action receive more blood, neurons that are more active should also receive more energy, man. And that’s it: there’s no need to worry about supply and distribution chains in the brain.

It would be great if it were true. In practice, we have found that the functioning of the brain is doubly limited. In the entry of blood through the internal carotid artery, which always passes the same volume of blood per second, and in the local distribution. The brain is like a city served by a single avenue through which all the cars pass, in constant flow, which are the exclusive distributors of all food and water to each of the houses on the edge of all the streets. A traffic jam on the main avenue is catastrophic, of course.

But a crater or roadblock on any street is also immediately challenging, especially since homes in this town immediately consume all the water and food they can get out of cars as they drive by. There are barely any leftovers or reserves. Terrifying, no?

The image explains why clinical neuroscience begins to be concerned with the health of capillaries, the streets of the brain, in addition to the great arteries, or avenues, which have been the focus of research on ischemia and infarction.

But there are far more implications. Doug and I have suggested that the brain’s economy is so limited by the distribution of resources that an extra effort here is possible, yes—at the expense of a momentary reduction there, always. The priority dedication of cognitive resources to a focus, which we call attention, is perhaps precisely the inevitable result of this bloodbath in the brain.

Over time, then, we are limited by the flow of blood through our brain capillaries to learn one thing at a time. Paying attention to two things at the same time is impossible. Our neurons are powerful, but the brain can only work in series.

I can only think of how it makes our time even more precious.