قشر فرونتال راست تقلید خشم را مختل می کند

The current study investigates the neural substrates of facial expression mimicry by assessing individuals with right and left lateralised frontal cortical lesions. Electromyography was used to measure spontaneous changes in electrical activity over the corrugator supercilii (brow) and zygomaticus major (cheek) muscle regions in response to happy and angry facial expressions. Individuals with right (n = 4) and left (n = 5) frontal cortical lesions and demographically matched controls (n = 9) were compared. It was shown that while all three groups mimic happy facial expressions, only controls and individuals with left frontal lesions mimic angry expressions. These data are consistent with evidence for right frontal cortical specialisation for the processing of anger.

Viewing a facial expression spontaneously induces a congruent facial reaction in the observer (Dimberg, 1982 and Dimberg and Lundquist, 1988), even when the observed face is not perceived consciously (Bailey and Henry, 2009 and Dimberg et al., 2000). Most investigations of the human neural substrates of this mimicry phenomenon have focused on the imitation of hand and finger movements, and only a handful have assessed facial expression mimicry. The first of these studies found that explicit instructions to imitate facial expressions result in predominantly right lateralised inferior frontal gyrus activation (Lee, Josephs, Dolan, & Critchley, 2006). However, it is of particular interest to understand the neural mechanisms of spontaneous, as opposed to intentional, facial expression mimicry since it has been suggested that this type of behaviour facilitates successful social interaction, including interpersonal rapport ( Lakin & Chartrand, 2003) and emotion recognition ( Goldman and Sripada, 2005 and Oberman et al., 2007). Some studies do not find that this type of mimicry is associated with emotion recognition ( Bogart & Matsumoto, 2010), but they do show that it facilitates congruent emotions between interaction partners ( Blairy, Herrera, & Hess, 1999). Each of these potential functions of spontaneous facial expression mimicry is consistent with a motor theory of empathy (Leslie, Johnson-Frey, & Grafton, 2004). According to this theory, perceiving another's facial emotion spontaneously activates one's own motor representation of that emotion, which in turn facilitates recognition of, and empathy for, the observed emotion (Lipps, 1903 and Preston and de Waal, 2002). This form of motor mimetic responding is also considered a form of empathy in its own right (Blair, 2005), with studies showing that stronger facial expression mimicry is associated with higher levels of empathy (Dimberg et al., 2011 and Sonnby-Borgstrom, 2002), in particular when mimicry occurs via the corrugator (i.e., brow) region in the upper half of the face ( Harrison, Morgan, & Critchley, 2010). Disruptions of mimicry in groups with reduced capacity for empathising, such as autism ( McIntosh, Reichmann-Decker, Winkielman, & Wilbarger, 2006) and schizophrenia ( Varcin, Bailey, & Henry, 2010) provides further evidence for the link between mimicry and empathy. In a brain imaging study, Leslie et al. (2004) found that whereas passive viewing of a facial expression activates the right frontal cortex, explicit instructions to imitate results in bilateral frontal activation. This suggests dissociation between conscious left frontal control of facial musculature and right frontal involvement in spontaneous empathic mimicry. It has also been shown that observation of facial expression stimuli activates the right premotor cortex (Carr, Iacoboni, Dubeau, Mazziotta, & Lenzi, 2003), contributing to the suggestion that the right, but not left, frontal region may play an important role in spontaneous facial expression mimicry. The only other study to assess the neural substrates of spontaneous facial expression mimicry suggests that the frontal regions may be particularly important for the mimicry of angry, but not happy, facial expressions. Specifically, individuals with traumatic brain injury did not mimic angry facial expressions, and this was attributed to the involvement of ventral frontal damage in this type of injury (McDonald et al., 2011). However, there have been no lesion studies to date that have specifically investigated the role of the right frontal cortex in facial expression mimicry, which clearly seems an important next step in delineating the neural substrates of this behaviour. Indeed, Dimberg and Petterson (2000) show that mimicry of angry and happy facial expressions produces stronger muscle activity on the left than the right side of the face, suggesting right hemisphere dominance in imitative behaviour. In addition, individuals with injury to the right hemisphere are less able to produce positive and negative facial expressions (Borod et al., 1985 and Borod et al., 1986), and have difficulty recognising basic emotional expressions (Adolphs, Damasio, Tranel, & Damasio, 1996). Further evidence for the potential importance of the right hemisphere in processing facial expressions comes from a study showing improved recognition of emotional valence when expressions are presented to the left rather than the right visual field (Natale, Gur, & Gur, 1983). More specifically, it has been shown that a patient with focal right frontal trauma demonstrated impairment in recognition of, and autonomic responding to, angry expressions, as well as high levels of aggressive behaviour and difficulty understanding others’ anger (Blair & Cipolotti, 2000). Together with evidence that viewing angry facial expressions activates the right orbitofrontal cortex (Blair, Morris, Frith, Perrett, & Dolan, 1999), it has been suggested that the right frontal region represents a specialised system for responding to, and generating expectations of, others’ anger (Blair & Cipolotti, 2000). In contrast, activations in non-frontal regions have been associated with smiling to happy expressions (Lee et al., 2006), as well as with viewing happy faces (Phan, Wager, Taylor, & Liberzon, 2002). A further study shows that processing negative expressions results in greater orbitofrontal activity relative to happy expressions (Iidaka et al., 2001). These studies suggest that damage to the right frontal region may disrupt the mimicry of angry, but not happy, facial expressions. Spontaneous facial mimicry responses are generally detected in experimental settings using facial electromyography (EMG; measurement of changes in the electrical activity of muscles), which is sensitive to even subtle changes in facial muscle activity. Numerous EMG studies have shown that images of angry facial expressions evoke increased corrugator supercilii (i.e., brow) activity relative to images of other types of expressions. In addition, happy facial expressions elicit greater zygomaticus major (i.e., cheek) activity relative to other types of expressions. Using this technique, the present study was the first to assess spontaneous facial expression mimicry among individuals with lesions localised to either the right or left frontal cortex. It was predicted that right frontal cortical lesions would disrupt the spontaneous mimicry of angry, but not happy, facial expressions.