Science Questions

Does an octopus have one motor cortex with 8 sections, one for each arm, or just one brain to control them all?

We put this question to professor Scott Hooper, of the University of Ohio

A 2001 article in Science by Sumbre, Gutfreund, Fiorito, Flash, and Hochner has the answer. Octopus arms contain a very large number of neurons. To show that these neurons generate arm movements, Sumbre and her co-workers amputated octopus arms and then electrically stimulated nerves in the arms that normally carry information to the arms from the brain. This stimulation induced normal arm movement and, importantly, in many cases the movements did not begin until after the stimulation had ended. These experiments thus showed that signals from the brain trigger arm movements (they give the command to move), but it is the peripheral nervous systems (one in each arm) that calculate how to actually make the movements.

This is clearly a very efficient way to do things, because it means the brain can concentrate on the environment and responding to it, not on boring calculations about what muscles to activate. This same efficiency is present in human nervous systems. When we walk, it is spinal neural networks, not the brain, that calculate in what order and how strongly the leg muscles need to be activated to produce walking. The higher parts of the brain are thus free to do other things such as looking for predators, thinking, and talking on radios.

August 2007