A little medical info here. Each part of the body has its own nerve cell area in the brain. It is like a map. These areas can be measured for things like reaction time.
For instance the thumb and the baby finger have a quicker response time and the fingers in the middle are somewhat inhibited by the “crossfire” of the two outer fingers.
Scientists used an image on a monitor that represented all 10 fingers. The subjects had to press the corresponding keys to what was being marked on the image. The outside fingers were the fastest, the middle finger the slowest.