Compassion's Unity

My question is two-fold. First, I believe that *metta* is classified as a meditation object involving concentration. Yet, in this study, researchers suggest it is a mixture of focused attention (e.g. *shamatha*) and open monitoring (e.g. *vipassana*). **Does Buddhism suggest in certain passages or teachings that compassion is dual in this way?** More so, from my experience, compassion meditations deepens insight. Theravada involves a mixture of *shamatha* and *vipassana*, and the Mahayana involves (more so) a union of compassion and wisdom recognizing *sunyata*. I feel the depth of *metta* might occur from its union of concentration and insight (as suggested in the previous paragraph) and from *metta* itself and the realization of *sunyata* (implied by their merging promoted by the Mahayana). I feel all these things occur with *metta* in my experience. When talking about *metta* a researcher described the occurrence of gamma waves: > Davidson found their brainwaves showed never-before-seen levels of gamma, one of the strongest types of brain waves, theorized to appear when the different regions of the brain harmonize. **In Buddhism teachings and texts, is metta said to unite a variety of mental factors together?** Thank you