We reflect other people’s emotions through an ingrained, unconscious process. According to the facial feedback hypothesis, seeing a happy or angry face would make us contract or relax the appropriate face muscles to emulate that expression and better identify and experience the associated emotion. Since botox impairs some facial muscles from contracting in response to certain facial expressions, a group of researchers wondered whether it would also affect emotional processing.
To test their hypothesis, they injected Botox to (temporarily) paralyse the muscle which causes frowning in 10 women aged 33–40 years old and measured their brain activity when looking at faces displaying different emotions.
If you want to know how exactly Botox messed up with emotional processing, read the rest of the article at MappingIgnorance.org