The importance of movement in brain function

Movement is the bottom line when it comes to why we have a brain. And, likewise, movement is fundamental to stimulate, and even optimise, that brain:

“If you move about and you are a multicellular organism, then you have, at the very least, a primitive kind of brain. The importance for moving creatures of having some kind of brain is best illustrated by an observation initially made by the late Emperor Hirohito of Japan, for whom the study of marine life was a passionate hobby. The tunicate in question is known as a sea squirt. When it is an immature larva the sea squirt spends its time swimming around: not only is it capable of movement but it also has a primitive vibration-sensitive device, crudely comparable with an ear, and a primitive light-sensitive device, roughly analogous to an eye. In fact, the sea squirt could be said to have a modest brain. However, when it becomes mature, the sea squirt changes its lifestyle and attaches to a rock. It no longer has to swim around anymore, because it now lives by filtering seawater. At this stage the sea squirt actually performs the remarkable act of consuming its own brain.

The clue to brain function provided by this tale is that you only need a brain when you are moving. For stationary life forms, the brain is no longer necessary. The whole point is that for an animal moving around, there is an interaction with an environment that is incessantly changing. You need a device to tell you very quickly what is happening and, most importantly, to enable you to respond to what is happening, to get out of the way of predators or to chase after prey. So, the brain, in whatever shape, size, and degree of sophistication, is somehow connected in a very basic way to ensuring survival as both a consequence and a cause of movement.”

Prof. Susan Greenfield, The Human Brain: A Guided Tour (2000)