Parkinson's disease is a neurodegenerative disorder classically characterized by motor symptoms. Among them, hypomimia affects facial expressiveness and social communication and has a highly negative impact on patients' and relatives' quality of life. Patients also frequently experience nonmotor symptoms, including emotional‐processing impairments, leading to difficulty in recognizing emotions from faces. Aside from its theoretical importance, understanding the disruption of facial emotion recognition in PD is crucial for improving quality of life for both patients and caregivers, as this impairment is associated with heightened interpersonal difficulties. However, studies assessing abilities in recognizing facial emotions in PD still report contradictory outcomes. The origins of this inconsistency are unclear, and several questions (regarding the role of dopamine replacement therapy or the possible consequences of hypomimia) remain unanswered. We therefore undertook a fresh review of relevant articles focusing on facial emotion recognition in PD to deepen current understanding of this nonmotor feature, exploring multiple significant potential confounding factors, both clinical and methodological, and discussing probable pathophysiological mechanisms. This led us to examine recent proposals about the role of basal ganglia‐based circuits in emotion and to consider the involvement of facial mimicry in this deficit from the perspective of embodied simulation theory. We believe our findings will inform clinical practice and increase fundamental knowledge, particularly in relation to potential embodied emotion impairment in PD. © 2018 The Authors. Movement Disorders published by Wiley Periodicals, Inc. on behalf of International Parkinson and Movement Disorder Society.

According to embodied simulation theory, understanding other people’s emotions is fostered by facial mimicry. However, studies assessing the effect of facial mimicry on the recognition of emotion are still controversial. In Parkinson’s disease (PD), one of the most distinctive clinical features is facial amimia, a reduction in facial expressiveness, but patients also show emotional disturbances. The present study used the pathological model of PD to examine the role of facial mimicry on emotion recognition by investigating EMG responses in PD patients during a facial emotion recognition task (anger, joy, neutral). Our results evidenced a significant decrease in facial mimicry for joy in PD, essentially linked to the absence of reaction of the zygomaticus major and the orbicularis oculi muscles in response to happy avatars, whereas facial mimicry for expressions of anger was relatively preserved. We also confirmed that PD patients were less accurate in recognizing positive and neutral facial expressions and highlighted a beneficial effect of facial mimicry on the recognition of emotion. We thus provide additional arguments for embodied simulation theory suggesting that facial mimicry is a potential lever for therapeutic actions in PD even if it seems not to be necessarily required in recognizing emotion as such.

15Investigating depression-like conditions in animals is methodologically challenging, but also revealed that horses scored as withdrawn then remained significantly likely to display the 24 behaviour. We measured sucrose intake, a classic measure of anhedonia never previously 25 applied to horses. Flavoured sugar blocks, novel to these subjects, were mounted in each stall 26 and weighed 3h, 8h, 24h and 30h after provision. We predicted that if affected by depression-27 like states, the most withdrawn horses would consume the least sucrose. This prediction was 28 met (F1,18 = 4.65, two tailed p = 0.04). This pattern could, however, potentially reflect general 29 appetite levels and/or food neophobia. To control for these confounds, hay consumption was 30 measured over 5 days, as were subjects' latencies to eat a meal scented with a novel odour. 31Although low hay consumption and long latencies to eat scented food did predict low sucrose 32 consumption, statistically controlling for these confounds did not eliminate the relationship 33 between being withdrawn and consuming less sucrose (although reducing it to a strong trend): Table 1) that include low, hopeless moods, 49"not caring", social withdrawal, and fatigue (APA, 2013). These are present for many days or Miller et al., 2007, and sub-57 normal levels e.g. Strickland et al., 2002). 58In terms of aetiology, a common trigger is chronic stress, for instance that arising from 59 aversive life events or chronic pain or illness ( e.g. Banks and Kerns, 1996; Blackburn-Munro 60 and Blackburn-Munro, 2001;Tafet and Bernardini, 2003; Munce et al., 2006;Siegrist, 2008; 61 Hammen et al., 2009; APA, 2013). Two types of cognitive change can often be observed before 62 the illness fully develops, and these may act as mediators in some subjects, being hypothesised 63 to help cause the onset and/or maintenance of the disease (Beck, 1967; Gotlib and 64 Krasnoperova, 1998). One is 'learned helplessness', which is proposed to occur "when highly 65 5 desired outcomes are believed improbable or highly aversive outcomes are believed probable, 66 and the individual comes to expect that no response in his repertoire will change their 67 likelihood" (Abramson et al., 1978). The second involves negative biases in attention, memory 68 and/or judgment (Beck, 1967; MacLeod and Byrne, 1996; Gotlib and Krasnoperova, 1998). 69Thus depressed people are prone for example, to judge ambiguous stimuli as being unlikely to 70 be positive ('cognitive pessimism'), and to recall unpleasant memories more readily than 71 pleasant ones. 72The symptoms of depression may not be unique to humans. A Web of Science literature 73 search using the terms "rats" OR "mice" OR "monkeys" AND "depression" yielded over Engel, 2002 p174, Brune et al., 2006 Ferdowsian et al., 2011; Hennessy et al., 2014) 96 and maternally deprived monkeys ( e.g. Harlow and Suomi, 1974;Suomi et al., 1975; Hennessy 97 et al., 2014). Horses, too, have been suggested to sometimes display depression-li...