610 current experiment the cue to move was presented equi- distant from the index and middle ﬁngers of the video hand); also any trials in which participants did not attend are detected by checking for incorrect responses and for abnormally long or short reaction times, and these trials are excluded from the analysis. The suggestion that social priming affects inhibition of imitative responses was investigated in the current data by performing a ‘bin analysis’ on the reaction time data from the Imitation Task to investigate whether response speed interacts with the effect of the priming manipulation. The results of the bin analysis revealed that the effect of social priming, that was evident in adults, was seen only for slower responses. Following previous studies (see Catmur and Heyes 2010), we suggest that this pattern of data ﬁts a model of social priming affecting late processes related to inhibition, rather than an attentional process (where effects of social priming may be expected to be seen for even the fastest responses). Our results therefore suggest that, for adults, positive social attitude priming leads to the release of inhibition of imitative motor output and that this process does not occur for adolescents. At present, the functional mechanism by which imitation inhibition is reduced by pro-social priming is unknown; however, Brass et al. (2005) argue that imitation inhibition relies on appropriate distinction between motor programmes initiated by the self, and those initiated by observation of the other. It is possible therefore that the effect of pro-social priming is to blur the distinction between the self and other and thus reduce the potential for imitation inhibition. Previous research has shown that being imitated pro- motes pro-social behaviour (Chartrand and Bargh 1999), and consequently, it has been suggested that imitation is a non-conscious tool that individuals use instinctively to facilitate social interactions with others (Cheng and Char- trand 2003; Lakin and Chartrand 2003; Chartrand and Jeffers 2003). Ku¨ hn et al. (2010) investigated the mecha- nism by which being imitated may lead to pro-social behaviour using fMRI and found that observing another individual being imitated activated neural structures involved in reward processing such as the ventral MPFC and medial orbitofrontal cortex. These areas are some of the latest to develop and are structurally and functionally immature in adolescence (e.g. Blakemore et al. 2007; Shaw et al. 2008). Leighton et al. (2010) have suggested that imitation and social attitudes are part of a positive feedback loop in which pro-social attitudes generate imitation, and imitation and/or being imitated further increases positive social attitudes. Leighton et al. propose that this relation- ship may be either innate or a product of social learning: humans may have an innate tendency to mimic more when they are in an afﬁliative frame of mind, or they may learn through interaction with others that it is under these 123 Exp Brain Res (2011) 211:601–612 circumstances that imitation tends to be most rewarding. Accordingly, it may be the case that the adolescent brain develops in accordance with genetically pre-programmed changes and that the neural machinery for associating positive social attitudes with imitation is not fully devel- oped until adulthood. Alternatively, it may be the case that as adolescents gain more experience with the imitation/ positive social attitude positive feedback loop described by Leighton et al. the association between imitation and positive social attitudes is strengthened. Studies showing that learning is often accompanied by neural changes (see Galvan 2010 for recent review) highlight the possibility that the strengthening of an association between imitation and positive social attitudes may play a part in the devel- opment of the adolescent brain. Further studies are neces- sary to gauge relative contributions of genetically pre- programmed developmental changes and those triggered by changes in the social environment. The original, naturalistic, experiments demonstrating a link between pro-social attitudes and imitation (e.g. Lakin and Chartrand 2003) could not dissociate whether the effect of pro-social priming was speciﬁc to imitation or whether it could be explained by effector priming. Leigh- ton et al. suggest that the effect is speciﬁc to imitation since pro-socially primed adults were faster to conduct a hand- open response when observing a hand-open response rather than being faster to open their hand when observing any hand movement. However, the paradigm used by Leighton et al. did not include a test of effector priming and therefore cannot show whether pro-social priming acts speciﬁcally on imitation. To directly test whether social attitudes modulate effector priming, we included an Effector Prim- ing Control task. Supporting the hypothesis that social priming would have a speciﬁc effect on imitation, our Adult Group demonstrated a modulation of imitation by social priming, whereas effector priming was unaffected. The speciﬁc effects of social attitude priming on imitation are in line with the theory that imitation inhibition is a separate ability, unrelated to performance on more classical inhibition tasks (Brass et al. 2003) and which results in activation of distinct neural areas (Brass et al. 2005). Conclusion The current study shows that whereas pro-socially primed adults show greater imitation than non-socially primed adults, this effect was not found for an Adolescent Group. The lack of the social priming effect for the Adolescent Group may be a result of the immature development of social brain regions and/or of reduced experience of imi- tating and being imitated and the positive social attitudes that this can generate. Analysis of our Effector Priming