Motor cortex excitability correlates with novelty seeking in social anxiety: a transcranial magnetic stimulation investigation

Social anxiety disorder (SAD) is characterised by fear of scrutiny by other people, avoidance of social situations and vegetative/motor symptomatology. The correlation between reduced striatal dopaminergic (DA) function, SAD motor symptoms and the high occurrence of SAD in patients with Parkinson's disease (PD), suggests a link between SAD and movement diseases caused by dopamine dysfunction. However, little is known about the electrophysiological aspects of SAD. We applied single- and paired-pulse transcranial magnetic stimulation (TMS) to investigate excitatory and inhibitory mechanisms of the primary motor cortex (M1) in 15 SAD patients and the relationship between these neurophysiological measures and clinical symptoms or temperamental traits. Data were compared with those obtained in 15 age- and sex-matched healthy volunteers. SAD patients showed significantly higher harm avoidance scores and lower novelty seeking scores when compared to controls. TMS measures did not significantly differ between groups. However, in SAD patients the cortical silent period (CSP) duration and the amount of long-interstimulus interval intracortical inhibition were significantly correlated with the NS score. Accordingly with NS reduction and CSP shortening reported in PD, the relationship between NS levels and the excitability of inhibitory circuits of the M1 may support the hypothesis that DA dysfunction could underlie NS deficits in SAD. Furthermore, these data suggest that "trait variables" (i.e., NS) are more closely related to neurophysiological measures than SAD symptoms, which represent "state variables" linked to social performance.