Children who manifest higher levels of shyness or have 1 or 2 copies of the short allele of the serotonin transporter promoter gene appear to have a different pattern of processing affective stimuli of interpersonal hostility.

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Cerebral reactivity to facial expressions, anger especially, measured at different developmental stages by different techniques is associated with adolescence SAD. The 5-HTTLPR genotype affects the neural processing of interpersonal affective stimuli during development.

The ability to process and identify human faces matures early in life, is universal and is mediated by a distributed neural system. The temporal dynamics of this cognitive-emotional task can be studied by cerebral visual event-related potentials (ERPs) that are stable from midchildhood onwards. We hypothesized that part of individual variability in the parameters of the N170, a waveform that specifically marks the early, precategorical phases of human face processing, could be associated with genetic variation at the functional polymorphism of the catechol-O-methyltransferase (val 158 met) gene, which influences information processing, cognitive control tasks and patterns of brain activation during passive processing of human facial stimuli. Forty-nine third and fourth graders underwent a task of implicit processing of other children's facial expressions of emotions while ERPs were recorded. The N170 parameters (latency and amplitude) were insensitive to the type of expression, stimulus repetition, gender or school grade. Although limited by the absence of met-homozygotes among boys, data showed shorter N170 latency associated with the presence of 1-2 met158 alleles, and familybased association tests (as implemented in the PBAT version 2.6 software package) confirmed the association. These data were independent of the serotonin transporter promoter polymorphism and the N400 waveform investigated in the same group of children in a previous study. Some electrophysiological features of face processing may be stable from midchildhood onwards. Different waveforms generated by face processing may have at least partially independent genetic architectures and yield different implications toward the understanding of individual differences in cognition and emotions.

Genetic variation of the A118G polymorphism of the μ-opioid receptor gene (OPRM1) predicts individual sensitivity to social rejection and fMRI activation during simulated social rejection in adults, while data on these relationships during childhood are lacking. We investigated whether this polymorphism predicts childhood withdrawal - a predictor of sensitivity to social rejection -, and the face-specific N170 event-related waveform in response to facial expressions. Among facial expressions, 'anger' was expected to be particularly evocative, as it communicates social rejection. Forty-nine children aged 8-10 years were characterised for their OPRM1 genotype, their score at the Withdrawn Scale of the Child Behavior Checklist (CBCL), and for N170 latencies and amplitudes recorded during a task of implicit processing of happy, neutral, and angry expressions of other children. Children carrying the OPRM1-G allele had higher CBCL Withdrawn scores and enhanced N170 amplitudes in response to facial expressions. Multiple linear regressions showed that the Withdrawn scale score predicts larger N170 amplitudes at the Pz and C4 electrodes, only for the anger expression. Children who carry one or two copies of the OPRM1 G-allele are more likely to manifest withdrawn behaviours, and differ for electrophysiological responses to the early phases of processing affective stimuli.

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