Objective: To compare spontaneous facial expression of Happiness as measured by Action Units; AU6 (cheek raise) and AU12 (smile) between individuals with Parkinson’s Disease (PD) in off-medication (PDoff) and on-medication (PDon) states and Healthy Controls (HCs) using Automated Facial Expression Analysis (AFEA).

Background: Hypomimia is a common symptom of PD [1]. Individuals with PD have been judged as insincere due to an increased presence of a non-Duchenne smile (a smile with absence of cheek raise)[2]. Hypomimia is considered a levodopa responsive symptom[3] but findings have been mixed.

Method: 30 HCs (25M, 5F) and PD subjects (off/on medication) (26M, 4F) completed a video watching task (watching an amusing clip) and a speaking task (talking about the clip). Footage was analysed using Affdex AFEA. AFEA provided a score (%) pertaining to activation of Cheek raise (AU6)  and Smile (AU12)  which together are considered to form a genuine Duchenne smile and expression of ‘felt’ happiness [4].

Results: A Two-Way Mixed-Design ANOVA examined differences in Cheek raise and Smile activation across groups (HC, PDoff, PDon) in each task (see Figures 1 & 2). A significant main effect of Group was found. Bonferroni-corrected post hoc comparisons revealed that HCs exhibited significantly greater Cheek raise activation than both PDoff (p < .001) and PDon (p = .019), and significantly greater Smile activation than PDoff (p = .003) and PDon (p = .017). The Task × Group interaction was not significant- Cheek raise (p = .177), AU12 (p = .153), though PD groups exhibited larger task-related differences than HCs. A Two-Way Repeated Measures ANOVA found no significant effect of medication between PDoff and PDon Cheek raise (AU6)  (p = .085), Smile (AU12) (p = .486) though a small effect of medication on Cheek raise in speech was observed. Cheek raise was diminished to a greater extent than Smile in PD groups.

Conclusion: These findings confirm that production of a Duchenne happy expression is reduced in individuals with PD compared to HCs. Medication did not significantly enhance facial activation overall, though a limited effect was observed. Cheek raise (AU6) activation is more vulnerable than Smile (AU12)  in PD subjects, particularly in speech. This aligns with prior findings that individuals with PD produce fewer Duchenne smiles during social interaction [5]. Future research might explore subtle medication effects on facial expressivity, particularly in speech-based tasks.

Figure 1

Figure 2

References: 1] Benno Schwartz, The natural history of the Parkinson’s disease in early stages. Logos Verlag, 2011.
[2] M. C. Smith, M. K. Smith, and H. Ellgring, “Spontaneous and posed facial expression in Parkinson’s disease.,” Journal of the International Neuropsychological Society, vol. 2, no. 5, pp. 383–391, 1996, doi: https://dx.doi.org/10.1017/S1355617700001454.
[3] L. Ricciardi et al., “Hypomimia in Parkinson’s disease: an axial sign responsive to levodopa,” Eur J Neurol, vol. 27, no. 12, 2020, doi: 10.1111/ene.14452.
[4] P. Ekman, R. J. Davidson, and W. V. Friesen, “The Duchenne Smile: Emotional Expression and Brain Physiology II,” J Pers Soc Psychol, vol. 58, no. 2, 1990, doi: 10.1037/0022-3514.58.2.342.
[5] T. K. Pitcairn, S. Clemie, J. M. Gray, and B. Pentland, “Non-verbal cues in the self-presentation of Parkinsonian patients.,” British Journal of Clinical Psychology, vol. 29, no. 2, pp. 177–184, 1990, doi: https://dx.doi.org/10.1111/j.2044-8260.1990.tb00867.x.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/assessment-of-hypomimia-in-parkinsons-disease/