Modulation of amygdala activity for emotional faces due to botulinum toxin type A injections that prevent frowning

Abstract

According to the facial feedback hypothesis, when we see an angry or happy face, we contract or flex the relevant muscles to recreate the expression to assist in identifying and experiencing the emotion reflected. We investigated the facial feedback hypothesis by using botulinum toxin type A (onabotulinumtoxinA; onabotA) injections to induce temporary paralysis in the glabellar muscles (responsible for frowning) and measured functional brain activity during the processing of emotional faces. Ten females viewed pictures of happy and angry faces during two functional magnetic resonance imaging (fMRI) scan sessions: one prior (Pre) to onabotA and one following (Active) onabotA injections. We found Pre vs. Active onabotA modulation of activity in the amygdala for both happy and angry faces, as well as modulation of activity in the fusiform gyrus for happy faces. Consistent with our predictions, preventing frowning through inhibition of glabellar muscle contraction altered amygdala processing for emotional faces. The modulation of amygdala and fusiform gyrus activity following onabotA may reflect compensatory processes in a neuroanatomical circuit involved in emotional processing that is engaged when facial feedback is impaired. These data contribute to a growing literature suggesting that inhibition of glabellar muscle contraction alters neural activity for emotional processing.Clinical Trials.gov registration number: NCT03373162.

Botulinum Toxin Injections for Psychiatric Disorders: A Systematic Review of the Clinical Trial Landscape

“…Interestingly, while clinical trials have been successful at establishing the efficacy of BONT-A for affective disorders using a variety of clinical tools and instruments, the field is generally lacking mechanism-oriented studies with patient populations. For instance, Stark et al (2023) [ 40 ] recently published a task-based fMRI study showing that BONT-A injections and inhibition of frowning alter the processing of emotional faces in the amygdala; these findings were confirmed in 10 healthy females. In psychiatric populations, only three fMRI studies so far have shown downregulation of the amygdala induced by BONT-A injections—notably, in MDD [ 13 , 14 ] and borderline personality disorder [ 15 ].…”

Machine Learning-Based Interpretable Modeling for Subjective Emotional Dynamics Sensing Using Facial EMG

“…Previously, some researchers have proposed mechanistic models to examine the association between subjective and facial emotion responses. For instance, facial muscle activations have been indicated to offer feedback to the brain regions, such as the amygdala, in the form of emotional proprioceptive signals [ 39 ]. However, few models specify the functions of associations among facial muscle activity, mediators, and subjective emotion states.…”

Botox (onabotulinumtoxinA) mechanism of action

“…[ 106 ] More recently, a study found that BoNT/A modulated the response of the left amygdala to viewing happy and angry faces, as well as the response of the right fusiform gyrus to viewing happy faces. [ 107 ] Another study found that corrugator muscle activity was positively associated with amygdala and negatively associated with ventromedial prefrontal cortex activity during the viewing of pictures designed to elicit negative emotions. [ 108 ] Finally, patients who responded to antidepressant medication showed a greater reduction of activity in the amygdala and several other brain areas than those who did not respond, indicating that early changes in emotional processing involving the amygdala and other structures are associated with clinical improvement.…”