It defines stimulus everything that can excite a body or part of it, causing a response or activation of the same. Our senses are continually affected by stimuli, that is, to change and to stress our system is ready to receive them in order to adjust to. In this optical stasis is not significant, or at least it is less of change: a stimulating treatment is based on the delivery of a stimulus to counteract precisely a situation of stasis and produce, as a result, a positive effect.