Botox may diminish the experience of emotion

11 Mar

Category: Neuroscience  • Psychology 
Posted on: April 16, 2010 7:15 AM, by Mo 

DO you smile because you’re happy, or are you happy because you are smiling? Darwin believed that facial expressions are indeed important for experiencing emotions. In The Expression of the Emotions in Man and Animals, he wrote that “the free expression by outward signs of an emotion intensifies it…[whereas]…the repression…of all outward signs softens our emotions.” This idea was subsequently elaborated by the great psychologist William James, who suggested that “every representation of a movement awakens in some degree the actual movement which is its object.”

Botox, which is used by millions of people every year to reduce wrinkles and frown lines on the forehead, works by paralyzing the muscles involved in producing facial expressions. A study due to be published in the journal Psychological Sciencesuggests that by doing so, it impairs the ability to process the emotional content of language, and may diminish the quality of emotional experiences.

David Havas of the University of Wisconsin-Madison and his colleagues have been investigating the relationship between emotion and language. In a study published in 2007, they covertly manipulated facial expressions by asking participants to hold a pen either in their teeth, to simulate smiling, or between their lips, to prevent them from smiling. This was found to affect the time taken to read sentences containing emotional content: reading times for sentences describing pleasant situations were shorter when the participants were smiling than when they were prevented from smiling, and this was reversed when they read sentences describing unpleasant situations. Thus, understanding of the  sentences was apparently enhanced when their emotional content matched the participants’ facial expression, and impaired when it did not.

Other researchers have shown that reading words describing emotions can activate the muscles involved in producing the facial expressions associated with those emotions. For example, reading negative emotional words causes contraction of the corrugator supercilii, which pulls the eyebrows down towards the centre of the face to produce vertical frown lines at the top of the nose, whereas reading positive emotional words activates the zygomaticus, which raises the corners of the mouth to produce a smile. These findings provide evidence that involuntary facial expressions can evoke emotions, and suggest that the brain mechanisms involved in experiencing emotions are also used in understanding the emotional content of language.

Following on from this earlier work, Havas recruited 40 women for the new study, all of whom were seeking first-time botox injections as a cosmetic treatment for frown lines on the forehead. These participants were asked to read sentences describing happy, sad or emotionally neutral situations. Immediately afterwards, they were taken to the physician, who gave them a single injection of botox into the corrugator supercilii, or “frown” muscle. (Botox acts by inhibiting the release of the neurotransmitter acetylcholine from motor neurons, leading to temporary muscle paralysis 24-48 hours later. Typically, the procedure is repeated after 3-4 months; with time, the muscles may atrophy, or waste away, through disuse.) Two weeks after the injection, the participants returned to lab to read another set of similar sentences.

The reseachers found that botox slowed the reading of the sentences containing sad emotional content, which, as the earlier work showed, would normally cause the frown muscle to contract. The reading time for the happy and neutral sentence was the same in both sessions. The researchers assume that the increase in reading time means that paralysis of the frown muscles hindered the participants’ understanding of the emotional content of the sad sentences. They also argue that their findings support the hypothesis that feedback from the muscles involved in producing facial expressions is critical in regulating emotional experiences.

The media have overstated the findings of this study, by reporting that botox can damage relationships and cause those that use it to lose friends. The results may suggest that botox can impair emotional reactivity, but this is by no means conclusive, and the news stories completely overlook the more profound implication of the results – that by paralyzing the muscles involved in producing facial expressions, botox may actually diminish the experience of emotion in those who use it. According to statistics compiled by the American Society for Plastic Surgeons, some 4.6 million people received botox injections in 2008 in the United States alone, making it by far the most popular cosmetic procedure. Given the widespread and unregulated use of botox, the findings suggest that further investigation of its possible effects on cognitive function is needed.


Havas, D., et al. (2010). Cosmetic use of botulinum toxin affects processing of emotional language. Psych. Sci. (in press). [PDF]

Niedenthal, P. M., et al. (2009). Embodiment of emotion concepts. J. Pers. Soc. Psych96: 1120-1136 [PDF]

Oberman, L. M., et al. (2007). Face to face: Blocking facial mimicry can selectively impair recognition of emotional expressions. Social Neurosci2: 167-178 [PDF].

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