Single Cell, Multiple Functions

Professor William Kristan explains that it is dangerous to ascribe a single function to a single cell, which may in fact be used for multiple purposes.

There are all kinds of dangers for assigning function. Even when you do the experiments the way we did and say "okay this cell is active while the animal is swimming," and in fact we know that some cells, when we stimulate them, they produce swimming. So, they are called command cells, so they command a behavior. They command the swimming and so that gets labeled a swim command cell. When we looked at other behaviors, looked to see what that cell did during crawling behavior or during shortening behavior, that cell was active during that behavior too. And so, what we are finding is that cells get recycled, neurons get used for a lot of different behaviors. We call it multiplexing, they are used for multiple functions. What they actually do, what part they have in behavior depends on what other cells are active too. If you say this cell is a swim command cell, you might overlook the fact that it is actually doing something much more complicated than that. I think that’s the biggest danger because I think nervous systems of any level of complexity, and ours is by far the most complex, are probably doing that all the time. The nervous system is using the same cells. Most of the cells in our brain are getting used for several different behaviors and I think that’s one of the reasons why brains are different from computers that we tend to do things massively parallel in overlapping ways. It’s bad for doing quick calculations, computers are much better at doing that than we are, but it is better for making associations between things that we see and want to do or sentences that we start to say and catch ourselves in the middle of it, ideas that we have remind us of other things. I think the reason that happens so frequently in our brains is because we use the same cells, the same parts for different things. So, while we’re in the midst of using it for one thing, it reminds us of something else. And I think that’s a danger in trying to assign a function to a part of the brain or a given cell because it has probably got multiple functions.