"Should I stay or should I go?"

I've mentioned that dopamine drives motivation, and that more dopamine tends to reinforce actions. The brain isn't just a vat full of chemicals sloshing around, though: most of the space is taken up by brain cells. These neurons come in different shapes, but the basic mechanism is almost always the same: one end takes inputs, the other end sends output, and the parts in between decide whether or not to send an output based solely on the sum of the inputs.

This may seem too simple to account for thought and behavior, and indeed, most of the interesting behavior produced by the brain comes from the ways that neurons connect to one another. Neurons connect in complex patterns that are fairly consistent over time and across different people: if you scan my brain, your brain, and the brain of some random person on the street, you'll find the same basic connections in the same places. These connections can be thought of as computer circuits in some ways, and different parts of the brain have circuits that perform different tasks. Since people tend to develop the same circuits, we can examine them and figure out what they do.

Basal Ganglia circuit. Copyright Andrew Gillies.

One of the neural circuits relevant to dance is called the basal ganglia. It's the home of dopamine, where most of it is stored and released. It's also crucial for control of physical movement: for example, Parkinson's disease occurs when just one small part of the basal ganglia dies. This isn't a coincidence. As it turns out, dopamine levels in the basal ganglia determine whether we start a planned physical action or not: high dopamine levels lead us to act and carry out the current plan, while low dopamine levels stop us from acting, and may lead us to come up with a new motor plan that releases more dopamine. Parkinson's patients lose their dopamine-releasing neurons, so their constant low levels of dopamine leave them unable to act on any of their thoughts and plans.

It seems, then, that dance owes its popularity to this circuit on two different levels. On one level, dancing is a motor activity, and relies on this deep system of neurons for carrying out the intricate and detailed movements required. On another, more fundamental level, the decision to dance may be made at least partly by the balance of dopamine and the ways it affects the flow of signals in the basal ganglia. If oxytocin causes pleasant feelings and leads to more dopamine release during dance, then the basal ganglia make sure that the surge of dopamine leads to more dancing!