Final answer:
The sternocleidomastoid is the muscle typically massaged when focusing on the neck and decolletage area, as it is responsible for rotating and flexing the head.
Step-by-step explanation:
When massaging the neck and decolletage, the muscle that is typically addressed is the sternocleidomastoid. This muscle is significant in that it laterally flexes and rotates the head, and when both the left and right muscles work together, they are responsible for the flexion of the head. The sternocleidomastoid can be felt when placing fingers on either side of the neck and turning the head from side to side, indicating the origins of the muscle's movement. It also serves to divide the neck into anterior and posterior triangles when viewed from the side.