You can find this exercise on page 40 of the book Synergistic Golf.
Exercise Type: DYNAMIC STRETCH
Exercise Category: FLEXIBILITY, HEAD - NECK
Stand tall with arms hanging to sides and shoulders relaxed. Picture a string pulling the top of your head to the sky and rotate head looking to the right then to the left. Allow approximately 4 seconds to rotate from one side to the other. Keep chin elevated and focus on lengthening. Inhale in center and exhale on turn. Repeat 5 times in each direction.