motor cortex

The motor cortex is the strip of brain surface that plans and commands voluntary movement — the part that says "now lift the arm" and sends the order on its way. It runs as a band across the top of the brain, just in front of the deep groove that splits the front and back halves.

It is organized as a rough map of the body, sometimes drawn as a little distorted figure called the homunculus. Nearby patches of cortex control nearby parts of the body, and areas that need fine control — like the hand and lips — get an outsized share of territory. So where activity lights up roughly tells you which body part is being moved.

That orderly map makes the motor cortex the prime target for movement-decoding BCIs. The key trick: even when the body can't move, merely imagining or attempting a movement still stirs the matching region. A BCI can read that stirring and turn the intended-but-blocked movement into real action on a device.