Noradrenaline mediates amygdala activation in men and women during encoding of emotional material

Abstract

The amygdala is a pivotal structure in humans for encoding of emotional information, as shown by recent imaging studies. It is unknown which neurotransmitters are specifically involved in the human amygdala, although in animal studies noradrenaline was shown to be essential. In our study, participants received the betablocker propranolol (which blocks the noradrenergic response) or placebo when watching neutral to highly negative arousing pictures. Amygdala activation, monitored with functional magnetic resonance imaging (fMRI), increased with emotional intensity of the pictures under placebo condition. Betablockade selectively decreased amygdala activation for emotional pictures of the second highest category, but not for the highest or lower (neutral) category pictures. Two findings add to the existing knowledge in this area. First, the activation pattern in the amygdala under placebo condition shows a nonlinearity related to the emotional categories of the pictures. Second, propranolol disturbs this activation pattern in the amygdala. Explorations with respect to gender show a similar effect of betablockade on amygdala activation in both men and women, but a difference in its effect on long-term memory for emotional pictures. This study supports the hypothesis that the neurotransmitter noradrenaline also mediates amygdala activity in humans when processing emotional stimuli and that betablockers can disrupt the normal activation pattern in the amygdala.