Although our results imply sensorimotor system involvement

Although our results imply sensorimotor system involvement in facial expression processing, they do not give any indication of whether children explicitly recognized the expressions they observed. Explicit and implicit recognition of facial expressions are thought to be distinct processes (Mathersul et al., 2009), involving separate but overlapping networks of indole-3-carbinol regions (Adolphs, 2002; Habel et al., 2007). Explicit recognition is the volitional mapping of an observed facial expression onto a discrete category with an associated label, such as ‘happiness’ or ‘sadness’. On the other hand, implicit recognition involves the automatic activation of representations associated with a facial expression, including emotional and motor components (e.g. the ‘feeling’ of happiness and the motor commands used to smile). Investigating the explicit recognition of facial expressions in young populations with limited verbal capacities is very difficult, however, it has been shown that by three years of age, children do begin to accurately name expressions (Pons et al., 2004). This implies that children start to explicitly recognize certain facial expressions around this age, but measures such as naming may rely on additional abilities that are still developing. By 30 months of age, and indeed much earlier (Farroni et al., 2007), children are capable of producing and show implicit recognition of all basic facial expressions, including those used in this study (Leppänen and Nelson, 2009). There are many event-related EEG studies that support implicit recognition of various facial expressions in infancy, which includes differentiation between emotional and neutral expressions (Leppänen et al., 2007; Taylor-Colls and Pasco Fearon, 2015; De Haan et al., 2004), as well as observational research showing that young children modulate their behaviour in response to the emotional versus neutral expressions of others (Nichols et al., 2010). Therefore, although we did not test explicit recognition in this study, children of this age do appear to implicitly recognize a number of facial expressions, and the differential mu desynchronization we found in response to emotional and non-emotional facial expressions suggests a role for the sensorimotor system in this process.
Funding This work was supported by a Medical Research Council UK doctoral studentship (MR/J003980/1) awarded to Holly Rayson.
Acknowledgements
Introduction From infancy to old age, humans have a fundamental need to form and maintain lasting positive relationships with others (Baumeister and Leary, 1995). Social exclusion frustrates this need and can lead to retaliation toward the sources of exclusion (Twenge et al., 2007), but may also lead to prosocial responses aimed at reconnection; both toward potential new sources of affiliation (Maner et al., 2007) as well as the peers responsible for exclusion (Will et al., 2015). The way people react to social exclusion has been hypothesized to be shaped through exposure to prolonged rejection by close others, such as parents (Feldman and Downey, 1994), or peers (London et al., 2007). Indeed, children and adolescents with a history of chronic peer rejection become increasingly more likely to defensively expect, readily perceive, and overreact to social rejection (London et al., 2007) and show a heightened neural reactivity to social exclusion (Will et al., 2016). Yet, how the neural responses underlying behavioral reactions to exclusion vary as a function of a history of chronic peer rejection remains to be investigated. Therefore, we examined neural processes involved in retaliatory (i.e. punishing) and prosocial (i.e. forgiving) reactions to social exclusion in adolescents with a history of chronic peer rejection and tested how they differed from adolescents with a history of stable high levels of peer acceptance. Peer rejection reflects the collective valence of negative sentiments in a group toward a specific individual in that group, which is most commonly assessed through asking group members who they like most (positive) and who they like least (negative) (Bukowski et al., 2000; Coie et al., 1982; Newcomb and Bukowski, 1983). Children who receive many negative nominations and very few positive nominations are classified as rejected and develop widespread impairments in daily life, ranging from conduct problems (Sturaro et al., 2011) to delinquency (Kupersmidt et al., 1995) and dropping out of school (Hymel et al., 1996). Transactional developmental models posit that such impairments arise out of a sustained pattern of reciprocal interactions between peers expressing dislike toward a rejected group member and the rejected member’s reactions to being disliked (Coie, 1990; Sandstrom and Coie, 1999). Social exclusion − defined as excluding someone from a group or activity − is one of the most common methods adolescents use to express dislike toward rejected peers (Coie, 1990). Transactional models predict that adolescents who react to exclusion with retaliatory vengeance might be more likely to elicit further rejection than those who show behavior aimed at reconnecting after exclusion. Preliminary support for this hypothesis comes from studies showing that adolescents with a rejected status report using more aggressive coping styles in response to social exclusion in a hypothetical scenario (Sandstrom, 2004). Elucidating the neurocognitive mechanisms underlying behavioral reactions to exclusion can further our understanding why some adolescents become trapped in a vicious cycle of chronic rejection and exclusion.