Electrical smiles spark better moods

Can the physical act of smiling make you feel happier? According to the facial-feedback hypothesis, it can. However, the idea that feedback from facial muscles can influence our emotions has been hotly debated, with research in the field producing mixed results. In 2016, for example, one of the best-known findings in support of the idea — that holding a pen in the mouth, to simulate a smile, made humorous cartoons seem funnier — notoriously failed to replicate.

In 2022, however, research by a global team that included sceptics as well as supporters of the facial-feedback hypothesis led to the conclusion that while holding a pen between your teeth is unlikely to change your mood, there is some evidence that smiling can make you make feel happier. And now, into this mix, comes a new study in Emotion, which found that using electrodes to stimulate some of the muscles involved in forming a smile or a frown affected the participants' mood.

Themis Nikolas Efthimiou at the University of Essex and colleagues studied 58 people, who across a series of trials, had electrical current applied to either their zygomaticus major muscles, which pull up the edges of the mouth, into a smile — or to their depressor anguli oris muscles, which pull the ends of the mouth down, into an 'unhappy' expression.

In some of the trials, the participants were also shown images. These content of these images was either emotionally neutral, or was chosen to match the expression being induced by the electrodes. In other words, sad images were sometimes shown when the ends of the mouth were being pulled down, and happy images were sometimes shown when their mouth was being made to smile. These participants also regularly rated their mood, on a scale from 1 to 100.

When the team analysed the data, they found that the highest levels of positive emotions were reported when the participants' mouths were being pulled into a smile and they were looking at happy pictures. However, even in the absence of positive imagery, stimulation of these smile muscles was still associated with feeling more positive emotion. The researchers also found that the lowest mood ratings accompanied stimulation of the depressor anguli oris 'frown' muscles, especially when the participants were also looking at sad images.

One note of caution about these results is that the size of the effect of muscle stimulation on emotional experience were small. However, the induced muscle movements were themselves small, the team writes. And they did not target all the facial muscles that are recruited for a smile or a frown, only a few around the mouth. If the induced smiles and frowns had been more pronounced, perhaps the effects would have been stronger, they suggest. Further research will be needed to explore this.

Still, these results clearly do contribute to the ongoing debate about whether facial muscle movements themselves have any impact on our emotions. "The finding that changes in felt emotion can be induced through brief and controlled activation of specific facial muscles is in line with the facial feedback hypothesis," the team concludes.

Read the paper in full:
Efthimiou, T. N., Baker, J., Elsenaar, A., Mehu, M., & Korb, S. (2024). Smiling and frowning induced by facial neuromuscular electrical stimulation (fNMES) modulate felt emotion and physiology. Emotion. Advance online publication. https://doi.org/10.1037/emo0001408

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