Draft of a short tale on the beauty and complexity of our brain

Draft of a short tale on the beauty and complexity of our brain

So you all have a unique copy of this most complex object in the known universe, the human brain. Forget today’s most powerful computers that send vehicles to Mars, reveal cosmic beauties to us with the James Webb telescope, highlight the Higgs boson or send drones to kill people on the other side of the planet . No, really, these technological achievements are nothing compared to that 1.4 Kilo bowl of Jello you have between your two ears!

Jello, you have to agree… In terms of consistency, the analogy is good, but not in terms of shape or complexity! Because there is no Jello mold capable of reproducing the convolutions of our cerebral cortex. If our cortex has all these folds and folds, it is above all a surface. A surface of 2-3 millimeters where a lot of neurons are concentrated, our famous “gray matter”. This surface, if unfolded, would be about the size of a large newspaper page. So how do we get that into our little skull? By crumpling it, of course! This crumpling however took place very gradually throughout evolution, the mouse or the rat not having for example a fold on the cortex, their cortical surface not being large enough to require these folds.

By the way, we don’t have time to tell this long story here, but did you know that you and your brain were of a “certain age”? Yes, I am happy to remind you that you were born 13.8 billion years ago! What ? Well, because we are all the fruit of a triple evolution: a cosmic evolution that allowed the atoms that make up your brain and your body to be built in the heart of the stars; a chemical evolution which began on the Earth shortly after its formation 4.5 billion years ago and which allowed chemical reactions to assemble these atoms to form the complex molecules which constitute us; and finally a biological evolution which allowed the emergence and the evolution of the living cell, this small chemical factory which spends its time repairing itself and producing the constituents which… are used to produce it!

Because, it must be said, we face a constant challenge, we living beings: disorder! Disorder, or entropy, or the 2e principle of thermodynamics which states that in a closed system, everything tends towards disorganization, that a cathedral will become a ruin of a cathedral a millennium later if we do not take care of it, but that a ruin will not spontaneously form a cathedral… Finally, you see the principle… All that to say that plants manage to rebuild themselves constantly directly thanks to solar energy, because they have chlorophyll which allows them to carry out photosynthesis, to seek the carbon atoms in the CO2 of the air and build with that. We animals don’t have a green complexion (except sometimes the day after waking…), and so we unfortunately don’t have any chlorophyll, so we have to perceive our environment and above all move around in it to find vegetable or animal molecules already constituted and which contain the carbon and the energy that we also need to keep us alive.

And there, casually, I have just revealed to you the origin of the nervous systems, that is to say this sensorimotor loop which allows us to perceive and move in the world! Then, the rest, mathematics, poetry or politics, it’s a bonus, it came after. Because if we look at the brain of a chimpanzee, our closest cousin, compared to ours, two things jump out at us. First the size: for a comparable body mass, our brain is three times larger! And then, thanks to all sorts of brain imaging techniques which I will spare you here, we realize that it is not the sensory or motor regions of the cortex that have expanded the most during the evolution of primates , but the so-called “associative” regions, those that make it possible to make links between our sensory neurons and our motor neurons. And people like that, we have a lot, a lot, a lot, a lot, a lot! They are the ones who will create this vast “mental space” which is specific to human beings and which allows us, among other things, to understand the stories we are told. To make us mental images, simulations, projections. In short, to invent new worlds and objects, a heavy trend in human beings…

But how many of these famous neurons do we have in our brain, are you going to ask me? At last count, we were talking about something like 86 billion neurons in each human brain. 86 billion neurons which will receive 100, 1,000, 5,000, sometimes up to 10,000 connections from other neurons! And there, I indulged in a little calculation. If we take a rather conservative number of 1000 connections per neuron, that would therefore be around 86,000 billion connections. What does big numbers like that eat in winter? To give you a first idea, do you know how long it takes to count to a million by going there with one digit per second? It takes about 11 days! And a billion? 32 and a half years old!! So I did a little calculation with astonishing result. I wondered how long that was 86 trillion seconds. Verification made, it is equivalent to approximately… 2.7 million years! So to count all the nerve connections in your brain at the rate of one per second, you would have had to start a little before the appearance of Homo habilis, the first representative of the genus Homo 2.5 million ago. years! We imagine him then, discovering that he can sharpen a flint by hitting it with another stone, at the rate of one blow per second… tchak… tchak…. tchak… And it’s only now, at this very moment, that he would finish counting the nerve connections in his brain! He would probably be very happy to have finally finished and his spear would probably be sharpened in criss, if you forgive me the expression…

As long as you are in delusions of grandeur, I have another question for you. If I put my two fists in front of each other like this, and I tell you that this represents a nerve connection, also called a synapse, then what would be the “scale” size of the human brain that would go with that? Big like the room here, like the whole building, the whole street corner? No. I did a little calculation again and it gave me around 40 kilometres! 40 kilometres, that’s about the distance from one end of the island of Montreal to the other. This means that if you leave Terrebonne to the east and drive for a good half hour to get to Sainte-Anne-de-Bellevue completely to the west, well you would see all along the road fists like that looking at each other, i.e. nerve connections, nerve connections, and more nerve connections… And not just east-west, north-south as well, and 40 kilometers up also, because the brain is a three-dimensional sphere, don’t forget that!

Two small things still to be in the impressive numbers about the brain. You know that neurons are cells like any other, but specialized cells for transmitting messages very quickly from one place to another. For this, they have developed two types of extension along which the nerve impulse will circulate: the dendrites and the axon. I’m going to show you this with a neuron model that I always have on hand, that’s the case, since it’s… my hand! Indeed, if I hold my hand with the fingers spread like that, each finger would represent dendrites, which usually receive the signal from other neurons; my hand would represent the cell body of the neuron, where all the small excitations received will, for example, converge; and my arm would represent the axon which can be very long and on which a nerve impulse will be triggered, for example if our cell body has received sufficient stimulation from other neurons. And that’s how the neurons will be able to excite each other and transmit information to each other. However, if we put all these little cables, all the dendrites and axons, end to end, it has been estimated that we could circle the Earth more than 4 times with the contents of a single human brain!

In closing I wanted to leave you with two metaphors about the brain. And no, it’s not the computer, especially not! The idea that our brain works “like a computer” may work very superficially, but the computer has no body to keep alive, and that very quickly prevents this metaphor from working well. I have a lot to say about that, and you can go to my website and my blog at www.lecerveau.mcgill.ca or by simply typing “the brain” on Google to find a lot of business that I wrote about it.

No, one of the best metaphors for our neuron forest, well, it is precisely… a forest! A forest where each tree represents a neuron, with its branches which form the dendrites, the trunk which takes the place of the cell body, and the longest root which goes deep into the earth would be the axon which goes to others neurons on the other side of the hill… or the neighboring cerebral convolution! The next time you go for a walk in the forest, imagine that you have been made tiny and that you are exploring the neuronal forest of your own brain… Dizziness guaranteed!

And as long as you are in the forest, if you come across a stream that runs down a good slope, stop for a moment to contemplate it. And tell yourself that it is not very different, basically, from all the global cerebral activity of your whole brain which then allows you to perceive this stream! Because the water flowing between the rocks and creating a lot of eddies is basically not so different from the incessant nervous activity of your billions of neurons. Like her, the water flows and agitates, but not just anywhere: it must go around the rocks and follow the bed of the stream. Just as our nerve activity is constrained by the large bundles of axons in our brain that it has no choice but to follow. But where this metaphor acquires its full force is when we see that it also works on another time scale. Because if we come back the following year or in ten years to see our stream, it won’t be quite the same. The water activity during all this time will have moved rocks, eroded the banks, so the water will follow a bit of another path. Well, so does the nerve activity in our brain, which also alters the efficiency of the nerve connections it crosses, strengthening the ones it often stimulates, weakening the less traveled smaller pathways. So all the time what our brain is basically doing is modifying itself. To integrate what he lives to constantly build the best models in the world. Like tonight here, for example, where I’m sure you’ll come out with a little different brain than you came in with. A brain perhaps a little more aware of its beauty, its complexity, and all that it allows us to tell and contemplate together.

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There will be no ticket next week for the reasons mentioned at the beginning of this one and because I am giving a lecture next Monday. Back, then, in two weeks. Until then, don’t forget to get your 86 billion neurons some fresh air while taking advantage of the beautiful autumnal light still present…

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