Introduction
muscle memory
The “facial feedback hypothesis” proposes that muscle memory in the face interacts with emotional regions of the brain, particularly the amygdala, and that this signaling is bidirectionalTo more directly evaluate the link between corrugator muscle activity and processing of negative emotions, several studies have attempted to inhibit those muscles via injections of botulinum toxin A (BoNTA). BoNTA injections cause a temporary relaxation of the muscles at the injection site by inhibiting the release of acetylcholine at motor nerve endingsSimilarly, several studies have suggested that peripheral BoNTA injections in the region of the glabellar muscles may be effective in treating major depressionIn addition, BoNTA injections in the glabellar region have been shown to modulate amygdala activity in response to the imitation of emotional expressionsHere, our aim was to better understand the effect of BoNTA (as onabotulinumtoxinA; onabotA) on functional activity in the brain during the processing of emotional faces. We first sought to test the hypothesis that onabotA injections would alter emotional-related activity in the amygdala, as shown by others