Overall, the current investigation provides evidence that spending more time with friends during adolescence is associated with less sensitivity to future social exclusion, as evidenced by dampened neural activity during social exclusion two years later in regions known to be involved in negative affective processing. These findings contribute to our understanding of how friendships may protect adolescents who experience peer rejection and are consistent with the notion that a high level of friend involvement during adolescence may contribute to beneficial outcomes later on.
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 (),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.
As a whole, the findings presented here indicate that spending more time with friends during adolescence relates to dampened affective neural responses to later social exclusion, and supports the possibility that greater friend involvement may result in individuals feeling less threatened when they encounter future negative social treatment. This work extends the developmental literature on the positive role of friendships during adolescence, and contributes to our understanding of potential mechanisms through which interactions with close others may yield positive benefits. Our hope is that these findings will help shape future behavioral and neuroimaging studies that continue to examine the interplay of social connection and responses to peer rejection during adolescence, in order to increase understanding of adolescents’ daily social interactions and the implications of these interactions over time.