Improbable can find but one formal scientific study which features investigations of fMRI monitored responses to meaningless lower-face acts (a.k.a. ‘gurns’). Experiments carried out in year 2000, under the protocols of the UK’s Bethlem Royal and Maudsley Hospital Research Ethics Committee, were designed to answer the question: ‘Can the cortical substrates for speechreading be distinguished from similar – but non-speech – face actions?’ The research, in which participants undergoing fMRI viewed stimuli of people speaking or gurning [see photo], showed that there can indeed be differences.
“Those areas activated more by observing gurning than speaking faces included [the] middle occipital gyri, middle temporal gyri, [and] fusiform gyri.”
See: “Cortical substrates for the perception of face actions: an fMRI study of the specificity of activation for seen speech and for meaningless lower-face acts (gurning)” by Ruth Campbell, Mairead MacSweeney, Simon Surguladze, Gemma Calvert, Philip McGuire, John Suckling, Michael John Brammer, and Anthony S. David, in: Cognitive Brain Research, 12, (2001) pp. 233–243.
Bonus Question [optional] ‘Are gurns always meaningless?’
BONUS: Intentional gurning may be a different kind of activity. Some people celebrate it. Here’s video of a British gurning competition: