Neuroanatomical correlates of social approach in Williams Syndrome and down syndrome

Individuals with Williams Syndrome (WS) or Downs Syndrome (DS) are often described as hypersociable, friendly and overly trusting of others. This hypersociability is a major concern for parents/caregivers due to the associated increased risk of exploitation and victimisation. Two brain regions - the amygdala and the orbitofrontal cortex (OFC) - have been implicated in driving this hypersociability in WS, and in the general population and have associations with emotional evaluation, threat detection and social motivation. However, there has been little neuroimaging research on this topic, especially in DS, to date. The aim of the present study was to investigate the potential neuroanatomical and neuropsychological correlates of hypersociability in WS and DS. Twelve individuals with WS (M = 22 years of age) and eleven individuals with DS (M = 26 years of age) completed a neuropsychological battery of executive functioning and social measures, including informant ratings on an ecologically measure of social approach. Clinical groups and twelve typically developing controls (M = 23 years) underwent a magnetic resonance imaging scan to investigate volumetric differences in the OFC and the amygdala. As expected, WS individuals displayed the highest overall social approach, especially in relation to need to approach strangers and drive to interact with strangers, as well as inappropriate/overfriendly behaviours. Both groups rated similarly in terms of social trust and unconditional positive regard. Emotion recognition abilities were similar across groups, with the DS group displaying some difficulties with negative emotions (especially anger). Inhibition and flexibility were similarly impaired across WS and DS. Compared to neurotypical controls, the DS group showed increased amygdala volumes bilaterally, while the WS group showed an enlarged right medial OFC. Approach ratings were significantly correlated with left amygdala and medial and left lateral OFC volumes in WS, and with these same regions bilaterally in DS. Results provide potential biological explanations for the hypersociability seen in WS and DS. Future research should focus on other potential neural correlates, as well as potential genetic and hormonal contributions to approach.