A recent Science article by Berton et. al. shows that long lasting fearful and withdrawal behaviors that are induced in mice by bullying and intimidation are enabled by a nerve growth factor (BDNF, brain derived neurotrophic factor) acting in the mesolimbic dopamine reward pathway in the brain. When a genetic trick is used to knock out DBNT production in just this area, mice are no longer intimidated by bullies. Elsewhere in the brain BDNF is associated with an opposite effect, antidepressant actions. The authors point out that the brain's reward system has been slighted in research on emotional disorders, even though the inability to experience rewarding feelings is a hallmark of depression and emotional withdrawal.