Traits are represented in the medial prefrontal cortex: an fMRI adaptation study

Neuroimaging studies on trait inference about the self and others have found a network of brain areas, the critical part of which appears to be medial prefrontal cortex (mPFC). We investigated whether the mPFC plays an essential role in the neural representation of a trait code. To localize the trait code, we used functional magnetic resonance imaging (fMRI) adaptation, which is a rapid suppression of neuronal responses upon repeated presentation of the same underlying stimulus, in this case, the implied trait. Participants had to infer an agent's (social) trait from brief trait-implying behavioral descriptions. In each trial, the critical (target) sentence was preceded by a sentence (prime) that implied the same trait, the opposite trait, or no trait at all. The results revealed robust adaptation from prime to target in the ventral mPFC only during trait conditions, as expected. Adaptation was strongest after being primed with a similar trait, moderately strong after an opposite trait and much weaker after a trait-irrelevant prime. This adaptation pattern was found nowhere else in the brain. In line with previous research on fMRI adaptation, we interpret these findings as indicating that a trait code is represented in the ventral mPFC.