Recent research into the “facial feedback hypothesis” using Botox injections to the forehead has found that the injections can change the way the brain interprets and processes other people’s emotions. This may mean people's ability to understand the expression of emotions is temporarily impaired due to disruption to neuromuscular feedback. 

The facial feedback hypothesis states that, when we see an angry or happy expression on another person’s face, we flex or contract the muscles in our own face in order to simulate the expression. This is an unconscious process. As our facial muscles mimic another person’s smile or scowl, signals are sent to our brains to help us interpret them. This is thought to not only assist in our ability to identify other people’s emotional states, but to experience them ourselves. 

The idea is often believed to have started with Charles Darwin when he conjectured over the origins of emotions. Darwin hypothesized that the expression or repression of emotions on one’s face would directly affect the experience of said emotion. 

For some, this has led to the idea that emotions are expressed in universal ways across the human race, though this has been hotly debated. Nevertheless, the facial feedback hypothesis suggests that there is a connection between muscle memory in the face and the processing of emotions in our brains. 

A team of researchers from the University of California, Irvine, published a study that investigated the feedback hypothesis by using Botox injections on a group of 10 female participants, each aged between 33 and 40. They injected the women to induce temporary paralysis in the glabellar muscle (which is responsible for frowning) and then measured their brain activity while they observed images of emotional faces. 

During functional magnetic resonance imaging (fMRI) scan sessions – one prior to their injections and one two weeks after the procedure – the participants were shown photos of happy and sad faces, along with neutral expressions. 

The researchers found that activity in the amygdala, the center of our brains responsible for emotional processing, showed signs of change when seeing happy and angry faces after the Botox injections. They also saw alterations in the fusiform gyrus, part of the inferior temporal cortex that helps with object and facial recognition, when the participants saw happy expressions. 

The results show that preventing frowning through Botox injections inhibits the way the brain processes emotional faces. Botox paralyzes muscle movement, which seems to disrupt the modulation of activity between the face, the amygdala, and the fusiform gyrus. 

There have been other studies into the impacts Botox has on emotional processing. A 2011 study found that people who received Botox injections to the forehead and area around the eyes where crow’s feet form experienced significant impairment in emotion perception, compared to others who only underwent procedures that do not affect feedback (such as dermal filler). 

Another study found that people took longer to read sentences containing emotional language.  

Yet other research has found that the inability to frown could also help patients suffering from depression. Although the underlying therapeutic mechanism for why this treatment helps ease depression symptoms is still not clear, it appears to be a potentially safe and effective means of managing depression. More research is of course needed before we draw any conclusions.

The study is published in Scientific Reports.