Neuronal activity of the supplementary motor area (SMA) during internally and externally triggered wrist movements.

The activity of neurones was recorded from the supplementary motor area (SMA) of monkeys while they were performing a discrete, arbitrary wrist movement. The cells responded similarly whether there was a triggering stimulus at the time of the movement or not. This experiment indicates that SMA neurones are active both in relation to externally triggered and internally initiated (voluntary) actions.