Abstract
The treatment of glabellar lines with botulinum toxin type-A (BoNT-A) is a staple for aesthetic providers who specialize in facial rejuvenation. Clinical efforts are currently underway to substantiate upper facial injections (the corrugator muscles are the target muscles) of BoNT-A as an antidepression therapy. This article describes the origin of "facial feedback" by Charles Darwin nearly 150 years ago, as well as "emotional proprioception"-2 neuroanatomical concepts that help provide the scientific rationale behind the general influence facial muscles have on the emotional centers of the brain, and, specifically, how the corrugator muscles-involved with frowning-promote a gloomy mood. The journey researchers have taken to clinically qualify BoNT-A injections of the corrugator muscles-to inhibit frowning, and thereby mitigate depression-will also be highlighted so that aesthetic providers are up to date on this emerging benefit of BoNT-A.