Spontaneous and intentional trait inferences recruit a common mentalizing network to a different degree: spontaneous inferences activate only its core areas.

This fMRI study analyzes inferences on other persons' traits, whereby half of the participants were given spontaneous ("read") instructions while the other half were given intentional ("infer the person's trait") instructions. Several sentences described the behavior of a target person from which a strong trait could be inferred (trait diagnostic) or not (trait nondiagnostic). A direct contrast between spontaneous and intentional instructions revealed no significant differences, indicating that the same social mentalizing network was recruited. There was, however, a difference with respect to different brain areas that passed the significance threshold, suggesting that this common network was recruited to a different degree. Specifically, spontaneous inferences significantly recruited only core mentalizing areas, including the temporo-parietal junction and medial prefrontal cortex, whereas intentional inferences additionally recruited other brain areas, including the (pre)cuneus, superior temporal sulcus, temporal poles, and parts of the premotor and parietal cortex. These results suggest that intentional instructions invite observers to think more about the material they read, and consider it in many ways besides its social impact. Future research on the neurological underpinnings of trait inference might profit from the use of spontaneous instructions to get purer results that involve only the core brain areas in social judgment.