Neuronal coding of stimulus-response association rules in the motor cortex.

Two monkeys were trained to perform wrist movements to align a pointer with visual targets. In the spatially 'compatible' condition, monkeys had to point at the target position (left/right), whereas in the 'incompatible' condition, they had to point at the position opposite to the target. A large proportion of neurones recorded in the primary motor cortex showed changes in activity according to either the side of the target or the side of the movement. However, more than 40% of neurones changed their activity as a function of the stimulus-response mapping rule. Some of these neurones, being sensitive only to the stimulus-response compatibility effect, must therefore be viewed as specifically involved in the neural mechanisms that control the association process between sensory inputs and motor outputs.