There is emerging evidence showing that people who suffer from depression have improvement in their symptoms when they utilize Botulinum Toxin A to treat their glabellar lines, also called frown lines between the eyes. The mechanism is thought to be from a feedback loop to the brain. Above it was mentioned how smiling can actually make you happy; this is by releasing chemical signals to the brain telling you you are happy. When you utilize the glabellar muscles it is typically with feelings such as anger, frustration or sadness. By blocking this movement it's theorized that it may also block some of the negative emotions themselves.