But an author of the original report—published nearly three decades ago—says that the new analysis has shortcomings, and may not represent a direct replication of his work. The paper has been cited more than a thousand times, and has been followed by other research into facial feedback. In , for example, researchers reported that injections of Botox, which affects the muscles of facial expression, dampen emotional responses. Overall, the experiments found no difference in the way people with pen-induced smiles or frowns rated the cartoons. And 16 of the experiments tested enough people for there to be statistical confidence that even if the studies had been repeated many more times, the researchers would have found the same null result, says Eric-Jan Wagenmakers, a psychologist at the University of Amsterdam who led the analysis. But Strack disagrees.

Thank you for visiting nature. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser or turn off compatibility mode in Internet Explorer. In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript. Botulinum toxin BTX injections reduce muscle mobility and are commonly used to treat the appearance of glabellar frown lines.

Thank you for visiting nature. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser or turn off compatibility mode in Internet Explorer. In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript. A crucial assumption that underpins this hypothesis is that mental states are shaped by information originating from the peripheral neuromotor system — a view operationalised as the Facial Feedback Hypothesis.