AGRP and obesity due to melanocortin 4 receptor deficiency: It was found that states of obesity cause long-lasting desensitization of AgRP neurons to dietary fat,180 and in fact, exposure to high-fat foods leads to a long-lasting devaluation of standard food chow via a persistently diminished sensitivity of the negative valence signal encoded by AgRP neurons and the positive valence signal encoded by dopaminergic VTA neurons to standard food.181