Synaptic competition

Professor Jeff Lichtman introduces the concept of synaptic competition, the process whereby nerve cells compete for space in the brain - much like protozoa in a very weird pond.

It probably would come as a surprise to most people to realize that the brain is made up of a bunch of nerve cells that probably don’t have any real idea that they’re part of your brain. They are singe-celled organisms not very different maybe from single celled organisms one finds in a pond, protozoa, that are living in a very weird pond, your mind, your brain, and they’re trying to get by, they are trying to survive. Like organisms that live in a pond the resources that are available to them are limited. In fact, there isn’t quite enough of anything for all of them to be happy. These nerve cells therefore have to undergo a period of time of competition and there are two main waves of competition in the nervous system of mammals (humans included) that are very important to us. The first takes place long before we’re born, when our nervous system cells, the neurons are first born, and they grow out to contact targets. Believe it or not there isn’t enough space in the targets for all those cells to survive and a substantial portion of the neurons that your brain generated when you were still a fetus, when you were still in the womb, die before you are born. About half the nervous system cells in our brain never make it to birth. So there is this phase of competition where only the most aggressive, perhaps, neurons that are most successful at getting what they need survive, and all the other neurons die. Then after birth, when the nervous system is first making its fine set of connections out in the world, there is a second wave of competition. This wave is extremely important to human beings. At the beginning of our lives our nervous systems are not built with the understanding of what it is that we are going to be doing with our nervous systems. Our nervous systems don’t know whether we’re going to be brought up in a world where we have to type, or speak English, or speak Chinese, or learn how to read, or live in a world with a particular kind of gravity. All of these things you might think the nervous system knew beforehand it does have no idea about it. So for humans, we have to some how shape our nervous system to the world around us. The way this is done is by nervous system cells each trying to make connections based on the experience the animal brings to bear. That competition between nerve cells leads to again a substantial number of the connections that are made early in life to be completely eliminated, and the ones that remain are essentially who we are. To put it in one other way, we start off with a nervous system wired up for any one of an infinite number of contingencies and possibilities, and then as we grow up in a particular world through competition between these nerve cells, a small subset of those connections survive, and everything else is trimmed away. That is who we become.