Introduction Emotion regulation has been broadly defined

Introduction Emotion regulation has been broadly defined as the monitoring, evaluation and modifying of emotional reactions in order to accomplish goals (Thompson, 1994). This can include both implicit emotion regulation, i.e. processes which occur automatically and largely outside conscious awareness and occur at very early stages of the emotion regulation process, and explicit emotion regulation, which involves using conscious strategies to modify emotional responses (Gyurak et al., 2011). Fully functional emotion regulation requires the ability to recognise the emotional significance of perceived stimuli, to appreciate the need for regulation, and then to select and implement an appropriate strategy (Sheppes et al., 2015). As such, it requires the co-ordination of multiple high-level processes including executive functions (Kesek et al., 2009) and in some cases social cognitive skills such as perspective taking. Adolescence (approximately spanning the ages 10–19; Sawyer et al., 2012) is of considerable interest from an emotion regulation perspective for several reasons. Developmentally, this period is associated with significant biological and physical changes, a growing need for independence, academic and employment pressures and fluctuating social relationships (Casey et al., 2010). These challenges are often accompanied by increased emotional reactivity and stress. As will be discussed in more detail below, it has been hypothesised that ongoing rsk inhibitor development renders adolescents less able to successfully regulate their emotions, putting them at greater risk for anxiety and stress related disorders (Powers and Casey, 2015). Indeed the period of adolescence has been associated with an increasing incidence of internalising and externalising symptoms (Lee et al., 2014; Paus et al., 2008; Spear, 2000). This suggests that adolescents may be particularly vulnerable to emotional dysregulation, although it is worth noting that, as with adults, it can be difficult to distinguish whether these behaviours result from poor regulation, increased affective responses, or both. Cognitively, high-level executive and social processes needed for emotion regulation, including working memory, inhibitory control, abstract thought, decision making and perspective taking, all undergo development during adolescence (e.g. Blakemore and Robbins, 2012; Dumontheil, 2014; Sebastian et al., 2010a; Somerville and Casey, 2010). Development of these cognitive processes appears to be underpinned by structural and functional development at the neural level, particularly in the protracted development of parts of prefrontal cortex and the remodelling of connections between prefrontal and limbic regions (see below). Simultaneously, adolescents are learning to negotiate increasingly complex social contexts (Sebastian et al., 2010a; Vartanian, 2000). It is possible that the interactions between these neurocognitive processes and social pressures could contribute to the observation that aspects of adolescent emotional processing and regulation development appear to follow a non-linear trajectory. In turn, this may at least partially explain increased emotional volatility and risk taking at this stage of life relative to both adulthood and earlier childhood (Casey and Caudle, 2013). Adolescence may therefore be a critical phase for the development of adaptive emotion regulation, with long-term consequences for future regulatory success and mental health. It has been suggested that adolescence is a period of heightened learning and flexibility (Casey et al., 2008; Steinberg, 2005). It could therefore be a critical phase for the development of adaptive emotion regulation strategies and in turn the implementation of interventions. Targeting this window of opportunity could have positive long-term consequences for mental health (Wekerle et al., 2007). This review will present mounting behavioural and neural evidence on the development of implicit and explicit emotion regulation in adolescence, and will highlight potential research directions. We will first briefly discuss the structural development of brain regions involved in the detection, expression and regulation of emotion across adolescence (see Blakemore, 2012; Giedd, 2008; Giedd and Rapoport, 2010; Lenroot and Giedd, 2006; Paus, 2005 for more comprehensive reviews of adolescent structural brain development). We will then review human behavioural and neuroimaging data investigating the development of different aspects of emotion regulation, ranging from automatic implicit emotional control (e.g. the ability to filter out emotional information via attentional control mechanisms) through to explicit and effortful strategy use. This section of the review will broadly follow the Process model of emotion regulation (e.g. Gross, 1998), and the recent Extended Process model (Sheppes et al., 2015). fMRI evidence suggests that, while conceptually quite different, there may be continuities in the way these implicit and explicit processes are instantiated at the neural level (e.g. Drabant et al., 2009). It is worth noting that due to the existence of other comprehensive reviews in the field (Blakemore and Robbins, 2012; Casey and Caudle, 2013; Steinberg, 2008) we will not cover risky decision-making, although emotion regulation abilities doubtless play a role here.