Other studies (O’Connor et al., 2002, 2008; Najib et al., 2004) also found neurobiological changes in mourning that are distinct from changes in depression (e.g., activation of nucleus accumbens, activation of amygdala, variation in the monoamine oxidase A (MAO-A) promoter gene, variation in heart rate variability). Here, MAOA is linked to depressive disorder.