Update: Botulinum Toxin for Depression: More Than Skin Deep

Botulinum Toxin Treatment for Depression: A New Paradigm for Psychiatry

Multiple randomized double-blind placebo-controlled trials have shown that botulinum toxin A (BoNT/A), when injected into the frown musculature, is an antidepressant. This review outlines the conceptual narrative behind this treatment modality, starting with theory developed by Charles Darwin. We develop the concept of emotional proprioception and discuss how the muscles of facial expression play an important role in relaying valenced information to the brain's emotional neuroanatomical circuit. We review the role of facial frown musculature as the brain's barometer and transmitter of negatively valanced emotional information. The direct connections between the corrugator muscles and the amygdala are reviewed, and these provide a neuroanatomical circuit that is a logical target for treatment with BoNT/A. The centrality of amygdala dysfunction in the pathogenesis of many psychiatric disorders, and the evidence that BoNT/A modulates amygdala activity, provides the mechanistic link between BoNT/A and its antidepressant activity. Animal models of BoNT/A's antidepressant effects confirm the evolutionary conservation of this emotional circuit. The clinical and theoretical implications of this evidence, as it relates to the potential treatment of a broad range of psychiatric disorders by BoNT/A, is discussed. The ease of administration, long duration, and favorable side effect profile of this therapy is reviewed in the context of existing antidepressant treatments.

A multi-lab test of the facial feedback hypothesis by the Many Smiles Collaboration

Following theories of emotional embodiment, the facial feedback hypothesis suggests that individuals' subjective experiences of emotion are influenced by their facial expressions. However, evidence for this hypothesis has been mixed. We thus formed a global adversarial collaboration and carried out a preregistered, multicentre study designed to specify and test the conditions that should most reliably produce facial feedback effects. Data from n = 3,878 participants spanning 19 countries indicated that a facial mimicry and voluntary facial action task could both amplify and initiate feelings of happiness. However, evidence of facial feedback effects was less conclusive when facial feedback was manipulated unobtrusively via a pen-in-mouth task.

Does Blocking Facial Feedback Via Botulinum Toxin Injections Decrease Depression? A Critical Review and Meta-Analysis

Researchers have proposed that blocking facial feedback via glabellar-region botulinum toxin injections (GBTX) can reduce depression. Random-effects meta-analyses of studies that administered GBTX to individuals with depression indicate that, 6 weeks postintervention, GBTX groups were significantly less depressed compared to placebo groups ( d = 0.83) and pretreatment levels ( d = 1.57). However, we noted the following concerns: (a) effect sizes were extraordinarily large, (b) authors failed to provide information to compute 51% of relevant effect sizes, (c) 96% of effect sizes came from studies conducted by investigators with conflicts of interest, (d) there is some evidence of publication bias, and (e) studies used ineffective blinding procedures. These considerations suggest that confidence in GBTX as a treatment for depression is premature.