Fortunately, however, adolescents also gain many benefits from these extra hours spent with peers, including companionship, advice and respect (Buhrmester, 1996), and they become reliant on peers as a primary source of social support (Brown, 1990; Buhrmester, 1996; Rubin et al., 2006). While parents might not welcome this change, social support from peers carries with it a host of short- and long-term benefits that may help youth avoid the escalating threat of peer rejection during adolescence. For example, both having high-quality friendships and having a greater number of friends reduce the likelihood of future peer rejection during early adolescence (Hodges and Perry, 1999; Hodges et al., 1999). Moreover, peer rejection is less associated with negative mental health outcomes across time among adolescents with greater social support (Rigby, 2000) and among those who have close friendships (Hodges et al., 1999). Thus, ironically, having closer relationships with peers provides a supportive outlet for adolescents, even as the risk of encountering peer rejection increases.

Despite these positive implications of friend involvement during adolescence, it is unclear what mechanisms yield this positive impact in the face of peer rejection. Furthermore, it is unknown whether the benefits of friends during adolescence remain apparent later, after the transition to young adulthood. In the present investigation, we used a social neuroscience approach to examine the underlying affective processes through which friend involvement during adolescence might be protective in the face of later peer rejection. Specifically, we examined whether spending time with friends during high school was associated with dampened neural sensitivity to peer rejection 2 years later.

Neuroimaging techniques are particularly useful for examining the potential mechanisms through which various types of social support, such as friend involvement, might protect individuals during negative social treatment. For example, one possible mechanism that has recently garnered support is that individuals with more social support perceive social stressors as less threatening, because they feel more supported and cared for in general. As a result, they are less reactive to stressors and display a dampened affective response compared to individuals without social support (Cohen and Wills, 1985; Eisenberger et al., 2007b). Given our growing understanding of the specific neural substrates underlying negative social interactions, we can test how neural affective responses during these negative social interactions relate to varying levels of friend involvement.

In particular, both the dorsal anterior cingulate cortex (dACC) and the anterior insula have been consistently linked with individuals’ affective responses to negative social treatment. The dACC has been linked to social exclusion among young adults (Eisenberger et al., 2003; Eisenberger et al., 2007a, b, c; Kross et al., 2007; DeWall et al., 2010; Masten et al., 2010b) and among adolescents and adults high in rejection sensitivity (Burklund et al., 2007; Masten et al., 2009). The anterior insula has also been linked with social exclusion among both young adults (Eisenberger et al., 2003; Kross et al., 2007; DeWall et al., 2010; Masten et al., 2010a, b) and adolescents (Crowley et al., 2010; Masten et al., 2009, 2010a), as well as negative affective states more generally (e.g. Phan et al., 2004). Thus, to the extent that friend involvement leads individuals to perceive negative social interactions as less threatening, those who are more involved with friends should display less activity in the dACC and anterior insula during these interactions.

In support of this, one recent study demonstrated that daily involvement with close others was associated with dampened threat responses to social exclusion. Specifically, young adults who reported more frequent interactions with supportive others on a daily basis demonstrated reduced activity in the dACC during social exclusion (Eisenberger et al., 2007b). Given this concurrent link between daily social support and reduced responses to social exclusion in early adulthood, we aimed to extend this research by examining whether involvement with friends during adolescence—when peer relationships are particularly important—would lead to similar dampened responses to social exclusion during young adulthood. In particular, given that friends are considered a primary source of social support during adolescence (Rubin et al., 2006), we expected that adolescents who reported more involvement with friends would show less neural evidence of sensitivity to social exclusion 2 years later.

In order to examine friendship involvement during adolescence, we measured the amount of time that individuals spent with their friends outside of school using a daily diary. The amount of time spent with friends was considered a useful index of adolescents’ involvement in supportive peer relationships because both friendship quality (Mathur and Berndt, 2006) and friendship intimacy (Berndt and Perry, 1990) increase as more time is spent with friends at this age. Also, we were interested in examining time spent with friends during adolescence specifically, because of the heightened importance placed on maintaining peer acceptance at this particular stage of development (Brown, 2004).

Furthermore, given that social support and close friendships during adolescence are thought to provide long-term protection from the negative effects of peer rejection across time (Hodges et al., 1999; Rigby, 2000), we assessed whether time spent with friends during adolescence would relate to neural responses to peer rejection at a later time point. To assess this, 2 years after completing the daily diary, participants underwent an fMRI scan during which they were ostensibly excluded by two same-age peers. We examined social exclusion both because its neural substrates have been established in prior research (e.g. Eisenberger et al., 2003; Masten et al., 2009), and because excluding peers is one of the most dominant forms of peer rejection during adolescence (Coie et al., 1990). We predicted that, to the extent that individuals spent more time with their friends during high school—when peer relationships are particularly important—they would be less sensitive to social exclusion 2 years later and thus show less neural activity in regions typically associated with negative affective processing (e.g. dACC and anterior insula), compared to individuals who spent less time with friends.

To examine how daily reports of time spent with friends during high school related to neural affective responses to social exclusion two years later, we performed both ROI regression analyses focused on the specific regions of the dACC and anterior insula that were more active during exclusion (vs the control task), as well as a regression analysis across the whole brain. Together, these findings indicated that time spent with friends during adolescence was negatively associated with activity in the anterior insula and dACC during social exclusion. This is consistent with research indicating that interacting with supportive others relates to reduced social pain-related neural responses to social exclusion among adults (Eisenberger et al., 2007b), and with developmental research indicating that friend involvement during adolescence is protective in the face of peer rejection (e.g. Hodges and Perry, 1999; Hodges et al., 1999; Rigby, 2000; Kochenderfer-Ladd and Skinner, 2002). Notably, the current findings also support the possibility that the protective role of friends during adolescence might have a lasting impact. Of course, longitudinal neuroimaging studies are needed to test the benefits of friend involvement over time. However, our findings indicate that youth who spend a lot of time with friends are less neurally sensitive to negative social treatment as they enter early adulthood, and it is possible that this pattern reflects long-term advantages of friend involvement.

The current findings also support the notion that friend involvement may yield protective benefits among adolescents specifically by decreasing the degree to which social stressors are initially perceived as threatening. Some theorists have alternatively suggested that social support might reduce stress via enhanced emotional regulatory processes that attenuate affective stress responses (Cohen and Wills, 1985). However, the current findings provided little evidence of enhanced regulation associated with friend involvement (i.e. no positive correlations between time spent with friends and regulatory neural activity), despite heightened activity in regulatory regions during exclusion overall (Table 1),² and despite previous evidence that activity in these regulatory regions (i.e. prefrontal cortices) relates to less sensitivity to peer rejection (Masten et al., 2009), and relational aggression (Baird et al., 2010). Thus, one long-term outcome of friend involvement during adolescence may be desensitization to negative social treatment, rather than a heightened ability to regulate affective responses to social stressors.

There are several reasons why being rejected by peers might be perceived as less threatening among adolescents who spend more time with their friends. One possibility is that these individuals are simply less bothered by peer rejection because they know that they have reliable friends who care about them. For example, there is some evidence that peer rejection is particularly threatening during adolescence because of the heightened importance that these youth place on maintaining peer acceptance (Parkhurst and Hopmeyer, 1998). Thus, youth who spend a lot of time with friends may feel a strong sense of belonging and acceptance in relation to their particular group of friends, and be less concerned that negative interactions with others will threaten this acceptance. Over time, this feeling of acceptance may become internalized and continue to reduce the degree to which social stressors are perceived as threatening, even years later. On a related note, to the extent that social rejection increases the desire to reconnect with others (Maner et al., 2007), individuals with more friends may be somewhat buffered by the negative consequences of rejection because they have greater opportunities to reconnect with others after the rejection episode.

Alternatively, one recent study provided another interesting possibility. Nishina and Bellmore (2010) demonstrated that when adolescents witness others being rejected by peers, friends of the victim are the most likely witnesses to interfere with the rejection and provide help. Thus, adolescents who spend a lot of time with friends may have learned that more often than not, encounters with peer rejection are often resolved quickly due to the interference of a friend. Across adolescence, if these individuals were ‘rescued’ by their friends whenever the threat of peer rejection arose, they may have developed the belief that these encounters are ‘not that bad’, and thus, react less strongly to future instances of peer rejection even when there are no friends present. Although these possibilities cannot be explored with the current data, it would be useful for future research to examine how neural activity during social exclusion relates to feelings of belonging and acceptance, as well as support seeking and friend interactions immediately following the exclusion.

Future research should also examine other indices of friend involvement and social support during adolescence that might yield positive benefits in the face of peer rejection. For example, while time spent with friends outside of school is one useful measure of friend involvement at this age, it would also be interesting to examine how neural responses to social exclusion are impacted by the number of friends that adolescents have and the quality of their friendships (i.e. ‘best’ friends and reciprocal friends), given that each of these measures is known to be protective in the context of peer rejection (e.g. Hodges and Perry, 1999; Hodges et al., 1999). Furthermore, longitudinal studies examining these qualitative aspects of adolescents’ friendships could also explore the stability of these characteristics (i.e. adolescents’ ability to maintain high-quality friendships and peer acceptance) over time, in relation to neural responses to peer rejection. This work could examine the possibility that lower neural sensitivity to peer rejection is a general characteristic of individuals with more friends (and/or the reverse—that hyperactivation in dACC and anterior insula characterizes individuals with fewer or low-quality friendships), rather than a consequence of friend involvement during adolescence as we suggest here.

A related issue in the current study is that time spent with friends and neural sensitivity to peer rejection were each measured at only one time point. Thus, it will be particularly important for future studies to examine how these variables change across time, which could reveal directionality and causal links between friendship and sensitivity to peer rejection across adolescence as well as the long-term stability of these associations. As alluded to above, the correlational nature of this study cannot rule out the possibility that stable, trait-level factors not examined in the current study (e.g. social status, self-esteem, or the long-term maintenance of quality friendships) might lead some individuals to be both more involved with friends and less sensitive to peer rejection more generally. Additionally, while we suggest that friend involvement during adolescence may be particularly crucial—given the heightened reliance on friends at this age—measuring friend involvement both during adolescence and at the time of the peer rejection experience 2 years later could reveal whether friend relationships in adolescence are particularly important as a buffer against future rejection, or whether friend involvement at the time of a rejection experience might be equally beneficial. Thus, while the current findings are consistent with the notion that friend involvement during adolescence may reduce neural sensitivity to peer rejection, longitudinal research directly examining the long-term effects of friend involvement on neural sensitivity is needed to confirm this possibility and rule out other explanations.

In this study, it is also important to note that we make some inferences based on previous research linking brain activity with specific emotional processes, when interpreting the meaning of our findings. In other words, we suggest that the dampened brain activity in dACC and anterior insula among individuals who spent more time with friends during adolescence may be an indicator of lower levels of distress following rejection. However, we cannot be certain that the dACC and anterior insula activity observed in this study were in fact indexing feelings of distress—particularly given that activity in any particular brain region at any given time is likely indicative of multiple brain functions (Poldrack, 2006), and given our inability to obtain high-quality, subjective reports of distress to relate to this observed brain activity (note 2). Thus, while we believe that making these kinds of theoretically-grounded inferences is informative for both data interpretation and for formation of new research questions, additional work is needed to further investigate the meaning and directionality of the present findings.

Finally, future work should continue to explore other biological and neurochemical processes through which positive social relationships might yield long-term positive benefits. For instance, given recently discovered links between specific genetic polymorphisms and neural responses to social exclusion (e.g. MAOA and µ-opioid receptor-related polymorphisms; see Eisenberger et al., 2007c; Way et al., 2009; Sebastian et al., 2010), it would be useful to examine other neurochemical, as well as structural, brain processes that might be impacted by social interactions during adolescence. For example, social contact results in the release of endogenous opioids in the brain, which are known to have stress-reducing effects (Panksepp, 1998), and the dACC in particular has a large density of opioid-receptors (Vogt et al., 1995; Schlaepfer et al., 1998). Thus, one possibility is that repeated exposure to supportive others triggers the frequent release of opioids in the dACC and other threat-processing regions, and reduces threat sensitivity over time. Alternatively, interacting with supportive others may also impact the development of brain structures relevant for threat-processing. For example, animal research has indicated that when newborn rodents are separated from their mothers, neurotransmitter fiber systems in some brain regions (e.g. dACC) can be structurally altered in ways that may impact the function in these regions (Braun et al., 2000). However, cues indicating close proximity of the mother (i.e. hearing the mother’s voice) can prevent these changes (Ziabreva et al., 2003), suggesting that social connection may impact structural development of threat-processing regions over time. As such, examining how adolescent friend involvement affects µ-opioid-related and other neurochemical processes, as well as structural changes in specific brain regions, might reveal mechanistic pathways that mediate the link between positive social interactions and neural desensitization to social stressors.