Touch and personality: extraversion predicts somatosensory brain response.

The Five-Factor-Model describes human personality in five core dimensions (extraversion, neuroticism, agreeableness, conscientiousness, and openness). These factors are supposed to have different neural substrates. For example, it has been suggested that behavioral differences between introverts and extraverts can be explained by the fact that introverts exhibit an inherent drive to compensate for overactive cortical activity in reticulo-thalamo-cortical pathways. The current study examined if responses in somatosensory cortices due to tactile stimulation are affected by personality traits. Based on previous studies and theoretical models we hypothesized a relationship of extraversion with somatosensory responses in primary somatosensory cortex (SI). In order to test this hypothesis we applied nonpainful tactile stimulation on the fingers of both hands of 23 healthy young participants (mean 25 years, standard deviation ± 2.8 years). Personality traits were assessed according to the Five-Factor-Model (NEO-FFI). Neuromagnetic source imaging revealed that the cortical activity (dipole strengths) for sources in SI were closely associated with the personality trait extraversion. Thus, the less extraverted the participants were, the higher was the cortical activity in SI. This relationship was in particular valid for the right hemisphere. We conclude that personality seems to depend on primary cortex activity. Furthermore, our results provide further evidence for an inter-hemispheric asymmetry of the social brain.