Deficits in the Mimicry of Facial Expressions in Parkinson's Disease

Abstract

Background: Humans spontaneously mimic the facial expressions of others, facilitating social interaction. This mimicking behavior may be impaired in individuals with Parkinson's disease, for whom the loss of facial movements is a clinical feature.Objective: To assess the presence of facial mimicry in patients with Parkinson's disease.Method: Twenty-seven non-depressed patients with idiopathic Parkinson's disease and 28 age-matched controls had their facial muscles recorded with electromyography while they observed presentations of calm, happy, sad, angry, and fearful emotions.Results: Patients exhibited reduced amplitude and delayed onset in the zygomaticus major muscle region (smiling response) following happy presentations (patients M = 0.02, 95% confidence interval [CI] −0.15 to 0.18, controls M = 0.26, CI 0.14 to 0.37, ANOVA, effect size [ES] = 0.18, p < 0.001). Although patients exhibited activation of the corrugator supercilii and medial frontalis (frowning response) following sad and fearful presentations, the frontalis response to sad presentations was attenuated relative to controls (patients M = 0.05, CI −0.08 to 0.18, controls M = 0.21, CI 0.09 to 0.34, ANOVA, ES = 0.07, p = 0.017). The amplitude of patients' zygomaticus activity in response to positive emotions was found to be negatively correlated with response times for ratings of emotional identification, suggesting a motor-behavioral link (r = –0.45, p = 0.02, two-tailed).Conclusions: Patients showed decreased mimicry overall, mimicking other peoples' frowns to some extent, but presenting with profoundly weakened and delayed smiles. These findings open a new avenue of inquiry into the “masked face” syndrome of PD.

Altered Kinematics of Facial Emotion Expression and Emotion Recognition Deficits Are Unrelated in Parkinson’s Disease

“…These results, which are in keeping with previous findings, indicate that muscle hypoactivation and slower movements of the lower face in patients with PD than in HS during the expression of facial emotions (18, 19, 21). By contrast, the results of previous studies have shown that the ability of PD patients to voluntarily perform stereotyped movements, such as blinking, is relatively well preserved, there being no evidence of altered velocities or amplitudes (40, 41, 46).…”

“…The results also extend the observations reported in previous studies on PD patients by revealing kinematic abnormalities in spontaneous and posed smiling (13, 14, 18), as well as those of more recent studies on facial mimicry deficits, as assessed by EMG (19, 21). Voluntary facial movements, including expressions of emotions, are primarily mediated by primary and non-primary motor cortical areas in the frontal lobe through direct corticobulbar projections to the facial motor nucleus (11, 44).…”

“…The ability to mimic a facial expression shown in a picture (posed emotions) has been reported to be either normal (16) or impaired (15, 17, 18). However, there is a limited amount of information available regarding the objective assessment of facial expressions of the basic emotions in PD using neurophysiological techniques (16, 19–21). By contrast, facial emotion recognition has been extensively investigated in PD patients (22).…”

“…Impaired emotion recognition has consistently been reported for disgust (23–26), whereas data on other emotions are less concordant (27–33). One important issue that has yet to be clarified is whether a relationship exists between facial emotion expression abnormalities and facial emotion recognition deficits in PD and whether these two deficits share the same underlying pathophysiological mechanisms (19, 21, 34). This information would provide a deeper insight into the pathophysiology of altered emotional processing in PD patients.…”

Facial emotion recognition in Parkinson's disease: A review and new hypotheses

“…Thus, in addition to central disorders, emotional symptoms in PD may be induced by peripheral dysfunction associated with impaired facial mimicry. To our knowledge, only 2 studies tested this hypothesis 30, 133. By recording EMG responses during an FER task, authors showed that FER impairment was accompanied by disruption of facial mimicry in PD.…”