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Review Development of the self-concept during adolescence Catherine Sebastian, Stephanie Burnett and Sarah-Jayne Blakemore UCL Institute of Cognitive Neuroscience, 17 Queen Square, London WC1N 3AR, UK Adolescence is a period of life in which the sense of self changes profoundly. Here, we review recent behavioural and neuroimaging studies on adolescent development of the self-concept. These studies have shown that adolescence is an important developmental period for the self and its supporting neural structures. Recent neuroimaging research has demonstrated that activity in brain regions associated with self-processing, including the medial prefrontal cortex, changes between early adolescence and adulthood. These studies indicate that neurocognitive development might contribute to behavioural phenomena characteristic of adolescence, such as heightened self-consciousness and susceptibility to peer influence. We attempt to integrate this recent neurocognitive research on adolescence with findings from developmental and social psychology. Introduction: the self in adolescence Human adolescence begins at puberty onset and ends with stable commitment to an adult role [1]. As such, adolescence has both biological and psychosocial demarcations. Social psychology studies indicate that during and after puberty, children become increasingly self-conscious and more aware of, and concerned with, others opinions [2,3]. Recent empirical research has focussed on neurocognitive aspects of self-processing in adolescence. These studies point to continuing development of the self during adolescence, and an increasing integration between one s own and others mental states. Here, we describe the development of the self-concept (Box 1) and its neural correlates during adolescence, with a focus on the medial prefrontal cortex (MPFC), a brain region that has a key role in selfreflection [4]. We also consider how this development might be related to changes in perspective-taking and peer influence. Corresponding author: Blakemore, S.-J. (s.blakemore@ucl.ac.uk). A changing concept of the self There are two main sources of information that we use to build up a self-concept [5]. Direct appraisals of what we are like can be abstracted from our own reactions to past events and experience, whereas reflected appraisals result from our beliefs about how we are seen by others, a concept termed the looking glass self. Research in developmental psychology has shown that evaluation of oneself becomes more comprehensive and differentiated during childhood and adolescence [6]. By early adolescence, children are more likely to compare themselves with others and to understand that others are making comparisons and judgments about them; they also begin to place higher value on these judgments. Thus, the looking glass self starts to have a larger role in self-concept. During adolescence, interpersonal environments undergo rapid change and an individual takes on new social roles [7], both of which probably contribute to changes in the self-concept. Recent neuroimaging research indicates that developmental changes in the self-concept might also be because of neuroanatomical development (Box 2) and functional brain changes in regions involved in self-processing, as described in the following section. Neural correlates of the self in adolescence Neuroimaging studies of self-reflection in adults, in which participants think about their own attributes and preferences, have shown activation in a network of brain regions, with consistent activations in dorsal MPFC. For example, reflecting on one s own thoughts, or on personality trait adjectives that describe oneself, activates dorsal MPFC [8 11]. This is one of the brain regions that undergoes anatomical development during adolescence; a recent longitudinal MRI study revealed that the MPFC is one of latest developing regions [12] (see Box 2 and Figure 1). Recent developmental neuroimaging studies have begun to look at the neural correlates of self-reflection in children and adolescents. A functional magnetic resonance imaging (fmri) study compared young adolescents (mean age 10 years) and adults (mean age 26 years) on a task of self versus social knowledge retrieval [13]. Participants were scanned while they judged whether phrases such as I like to read just for fun, described either themselves (the self-condition) or a familiar other (in this case, the fictional character Harry Potter; the social condition). Adolescents activated the dorsal MPFC to a greater extent than did adults during the self-condition (Figure 2). By contrast, adults activated the lateral temporal cortex more than adolescents did during the self-condition. The authors [13] suggest that, given the part played by the lateral temporal cortex in semantic memory retrieval, adults use stored self-knowledge when performing the task more than adolescents do. By contrast, adolescents might rely more on on-line self-reflective processing performed by the MPFC [8 11]. This indicates that adolescents and adults use different neurocognitive strategies when making selfreferential judgments. In addition to being able to reflect on one s own attributes and preferences, the self-concept also comprises the ability to think about what you are likely to do in a given situation. A recent fmri study investigated the develop- 1364-6613/$ see front matter ß 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.tics.2008.07.008 Available online 18 September 2008 441

Box 1. Multiple selves There is no single unified definition of self [32]. Here, we focus on the development of one aspect of self: the self-concept. The selfconcept is defined as how one perceives oneself (e.g. I am outgoing ). The self-concept also includes the social self-concept, that is, one s perceptions of how others perceive them (e.g. people think I am shy ). This is sometimes referred to as the looking glass self [5]. More primitive aspects of self require less explicit self-reflection, and are present from an early age [33]. Even newborn babies seem to have some forms of implicit self-awareness, that is, they show signs of being able to distinguish between self and other. Within 24 h of birth, babies root (orient their face towards the source of tactile stimulation) more to external touch compared with spontaneous self-touch to the cheek [34]. By 5 6 months of age, infants show preferential looking to a pre-recorded video of another, same age infant, compared to a pre-recorded video of themselves wearing identical clothes [35]. At around 18 months, self-awareness becomes more explicit: there is evidence that children this age show signs of understanding that they exist as an individual, separate from other people. For example, children this age start to recognize themselves in mirrors [36]. In the second and third years, infants start to show an understanding that other people are similarly self-aware, and differentiate between themselves and other people in speech [37]. ment of this ability by asking participants to think about what action they would take, given a particular intention [14]. Adolescents (aged 12 18) and adults (aged 22 37) were scanned while answering questions about intentional causality (e.g. You want to see what s on at the cinema; do Box 2. MRI studies of the adolescent brain Recent structural magnetic resonance imaging (MRI) studies have shown that brain regions involved in self-related processing continue to develop during the second decade of life [38,39] (see Figure 1 in main text). The amount of white matter in various cortical regions, including the prefrontal cortex (PFC), temporal and parietal cortex, increases between childhood and adulthood [40]. This increase in white matter is thought to reflect continued axonal myelination [41]. At the same time, grey matter volume in several cortical regions decreases between childhood and adolescence [38]. Some MRI studies have found that grey matter volume follows an inverted U shape during adolescence [37]. An initial increase in grey matter volume, thought to reflect a period of synaptogenesis during childhood, gives way to a protracted decrease in grey matter volume, hypothesized to reflect synaptic pruning during adolescence [42]. These changes in the grey and white matter do not occur on the same timescale throughout the brain. Areas subserving primary functions, such as sensory or motor systems, tend to mature before puberty [40]. By contrast, higher order associative regions, including prefrontal, parietal and temporal cortices, are still maturing after puberty and this continues even into the twenties. A subset of these late-maturing brain regions are involved in selfrelated processing including MPFC. It has been proposed that these neuroanatomical changes contribute to the functional changes (increased prefrontal activity) between adolescence and adulthood reported in several fmri studies. The continued axonal myelination and pruning of synapses in certain regions in adolescence might render the neuronal circuitry more efficient so that less activity would be required to perform a given task [43]. This explanation might account for the decrease in activity in the MPFC in self-referential tasks between early adolescence and adulthood [13,14,21]. This idea is speculative and makes several assumptions about neuronal activity and its relation to the BOLD signal (see Ref. [44] for further discussion). Furthermore, it cannot account for brain regions such as the temporal cortex, in which activity increases with age according to several studies [13,14,21]. Figure 1. Cortical thickness development in MPFC data from a longitudinal study of 375 participants aged 3.5 to 33 years [12]. The figure shows cortical thickness trajectories across age in different regions of the right medial prefrontal cortex. Phylogenetically recent (isocortex) areas develop along a cubic trajectory with age (in red). More primitive regions follow either a quadratic trajectory (with an initial increase in cortical thickness followed by a decrease in green) or a simple linear decline in thickness (blue). For regions in which development followed a cubic or quadratic trajectory, cortical thickness peaks at an earlier age (around 7 years) in primary sensory and motor areas than in secondary areas. Parietal regions peak at around 9 10 years, whereas dorsolateral prefrontal, medial prefrontal (shown here) and cingulate cortices reach peak thickness last (around or after 10.5 years). Data from Ref. [12]. you look in a newspaper? ), or physical causality (e.g. A huge tree suddenly comes crashing down in a forest; does it make a loud noise? ). Consistent with the self versus social knowledge study described earlier, adolescents activated part of the dorsal MPFC more than adults did when thinking about their own intentions, compared to during physical causality judgments (Figure 2). By contrast, in the same comparison (intentional physical), adults activated part of the right superior temporal sulcus more than adolescents did. Therefore, these two studies show that during development there is a shift in the pattern of activity associated with self-reflection, such that MPFC regions are used more in adolescence and posterior temporal regions are used more in adulthood. There are several possible explanations for this shift in activation pattern. One possibility is that adolescents and adults use different neurocognitive strategies when performing the same task. A second possibility is that the functional brain changes are related to the neuroanatomical changes that take place during adolescence (Box 2). Development of perspective-taking during adolescence The looking glass self refers to the self as viewed by other people. Therefore, an increasing awareness of others perspectives might provide additional information from which to construct the self-concept. A behavioural study investigated the development of perspective-taking during adolescence [15]. Children (mean age 9 years), adolescents (mean age 13) and adults (mean age 24) were tested using a perspective-taking task that required the participant to imagine which of two emotions either she or he (firstperson perspective) or a protagonist (third-person perspective) would feel in various emotional scenarios. The results demonstrated that the difference in reaction time between first-person and third-person perspectivetaking decreased with age. This indicates that proficiency of perspective-taking improves between childhood and adulthood. Alternatively, as the self-concept becomes more coherent with age, adolescents might increasingly use the self as the basis for judging others. 442

Figure 2. Functional development of MPFC in self-tasks. Activity changes in MPFC between early adolescence and adulthood from two developmental fmri studies in which participants reflected on the self. (a) Activity in MPFC (Montreal Neurological Institute coordinates [MNI] coordinates 10, 54, 14) was higher in young adolescents than in adults on a task of self versus social (other) knowledge retrieval [13]. Participants were asked to indicate whether phrases accurately described them (self-condition) or a fictional, familiar other (social condition). (b) Activity in a similar region within MPFC (MNI coordinates 12, 42, 21) was more active in adolescents than in adults when thinking about one s own intentions and actions relative to thinking about physical events [14]. Increased awareness of others perspectives during adolescence might also be related to the imaginary audience. This term describes the phenomenon whereby adolescents believe that others are constantly observing and evaluating them [16], even if this is not actually the case. The New Look Theory [17,18] suggests that the phenomenon results from a combination of two processes. First, adolescents need to develop their own identity as separate from their parents (separation-individuation). As they begin to question who they are and how they fit in, they might become increasingly self-conscious, leading to the imaginary audience. Second, the development of social perspective-taking results in adolescents becoming increasingly aware that others have the capacity to evaluate them. This could subsequently lead them to overestimate the extent to which this actually occurs [19]. It should be noted that studies conducted more recently indicate that the imaginary audience peaks in adolescence but persists into young adulthood, and that even older adults exhibit some phenomena associated with it [20]. The ability to integrate the wider context in a social encounter is another form of perspective-taking that might affect self-concept. For example, to understand whether a remark is meant sincerely or ironically, an individual needs to be able to appraise the effect of recent events on the speaker s mental state, and use this to interpret their implied meaning. A recent neuroimaging study provided evidence that the neural processing underlying context-based inference in social encounters develops during adolescence [21]. Adolescents (aged 9 14) and adults (aged 23 33) judged whether a series of phrases (e.g. Nice going! ) were sincere or ironic. Adolescents showed stronger activation of the dorsal MPFC during this task than adults did. Adults activated posterior regions, including the superior temporal and fusiform gyri, more than adolescents did. This study shows that the pattern of neural activity associated with taking into account the wider context of a social encounter changes during adolescence. These results are similar to the developmental neuroimaging studies of self-processing described earlier, showing again that activity moves from anterior (dorsal MPFC) to posterior (temporal) structures with age. A similar result was found in a recent fmri study that investigated changes in the neural processing of social emotion in the first or third person perspective during adolescence. [22]. Adult (age 22 32) and adolescent (age 10 18) participants read scenarios that described either social emotions (guilt or embarrassment) or basic emotions (fear or disgust), and were asked to imagine these scenarios happening either to themselves (self-condition) or to someone else (their mother other condition). First, akin to the findings of several developmental social cognition studies reviewed earlier, activity in the dorsal MPFC during social emotion relative to basic emotion was higher in the ado- 443

Figure 3. Social emotion from the self- and other-perspective. Adults and adolescents imagined social and basic emotion scenarios (a) from their own or from their mother s perspective. A region within left temporo-parietal junction (b) differentiated better between self and other in adults than it did in adolescents [22]. lescent group than in the adult group. Second, the left temporo-parietal junction (TPJ) showed differential activity to protagonist and emotion, depending on age group (Figure 3). Specifically, this region differentiated better between self and other in adults than it did in adolescents, whereas in adolescents the left TPJ was more responsive to the difference between social and basic emotion irrespective of perspective. This finding indicates that the neurocognitive strategies for attributing social and basic emotions to self and other develop with age. A possible interpretation is that adolescents rely more heavily than adults do on a simulation-based strategy when imagining the emotional response of another person. Emotion regulation and resistance to peer influence It has been argued that positive social feedback becomes increasingly rewarding during adolescence and that negative social experiences can contribute to the increased incidence of affective disorders such as depression during this period of life [23]. A recent study showed that having a negative self-concept in adolescence (defined by high scores on measures of self-hate, self-neglect and self-blame) is associated with both internalising behaviours such as depression and anxiety, and externalising behaviours such as delinquency and aggression [24]. Regulating the distress associated with negative social events, in addition to other negative stimuli, is important in self-concept development. An fmri study recently looked at self-regulation of emotion, which relies on lateral and medial PFC in adults [25], in a group of children aged 8 10 years [26]. When the children voluntarily suppressed their emotional reactions to sad film excerpts, there was activity in a larger number of prefrontal regions than in adults. The authors [26] suggest that this change in activation pattern might be related to anatomical development within these regions (Box 2). Adolescence is a particularly important time for the self-concept to be shaped by other people, especially peers. Self-report studies have shown that adolescents find spending time with peers particularly rewarding and are particularly influenced by their peers [27,28]. Susceptibility to peer influence is thought to contribute to adolescents greater propensity to engage in risky activities, compared to other age groups [29]. Arecent behavioural study measured the incidence of risky driving events in a car simulation video game, in which adolescents and adults played alone or with two friends present [30]. For adolescents, the presence of peers more than doubled the number of risks taken, whereas for adults the presence of peers had little effect on risky driving. This empirical study corroborates anecdotal evidence that adolescents are more likely to make risky decisions in the presence of peers. A recent fmri study found that children (aged 10 years) with high resistance to peer influence showed greater functional connectivity between several brain regions when observing emotional (angry) gestures, compared to children with low resistance to peer influence [31]. This was interpreted as indicating that children with low resistance to peer influence scores were more reactive to emotionally laden actions. It would be interesting in future studies to investigate systematically how susceptibility to peer influence relates to self-concept and how its neural basis develops within the same individual over time. 444

Box 3. Outstanding questions - Are there gender differences in the development of the selfconcept during adolescence? - Does development of self-concept proceed through a series of discrete cognitive stages during adolescence? - How is the development of self-concept affected by individual differences in genetic background? - How does the environment influence development of the selfconcept and its neural correlates? - How is self-concept development related to neuroanatomical maturation, and how is this related to functional brain activity in adolescence? - Is the development of self-concept in adolescence related to the increased incidence of affective and anxiety disorders during this period of life? Conclusion Adolescence is an important period for development of the socially integrated self-concept. The evidence discussed here indicates that neurocognitive development during adolescence occurs in brain regions involved in reflecting on the self. 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