Anxiety and Depression

 

Three possible human threat situations apply to human fear processing and anxiety: 1) pre-encounter phase - when an animal or a human is moving around in an area where there may be threats, 2) post-encounter phase - when a threat has been identified but is not attacking and 3) circa strike phase - when a threat is attacking. While the pre-encounter and post-encounter phase are linked amygdala and bed nucleus of stria terminalis (BNST) the circa-strike phase is linked to the dorsolateral peri-aqueductal gray (dlPAG)  in the brainstem. Contrary, to the post-encounter phase which is linked to a passive behaviour the circa strike phase is associated with a active phase (fight-or-flight behaviour). While the pre- and post-encounter phases are linked to several anxiety processes the circa-strike phase is linked to panic attact. Finally, while there have been several human experimental models for pre- and post-encounter phases it has been very hard to develop experimental models for the circa-strike phase. We succeded to develop such an experimental model to study the circa-strike behaviour in humans while the brain activation was measured (Mobbs et al Science 2007; Mobbs et al Journal of Neuroscience 2008). Hopefully, these experiments will help us better understand the processes underlying panic-attacs in humans.

 

Reward processing is not functioning properly in depression as mirrored in symptoms of anhedonia. Reward processing has been postulated to depend on a “wanting-signal” and a “liking-signal”. While the wanting signal is dopamine dependent and involved in increasing salience of a reward (and thereby the willingness to work for the rewards) the liking-signal is opioid dependent and involved in the subjective experience of reward. There are several similarities between the “wanting-signal” and expectations. Both predict future outcomes and shape behavior in accordance to this. Also, the dopamine system seems to be a key aspect in both processes. In fact, “wanting-signal” is closely associated to reward expectations. Thus, it may be suggested that a similar dopamine dependent expectation and salience system is involved in reward processing as in the placebo effect. The division between wanting system and liking systems may be associated with melancholia and anhedonia in depression, respectively. However, the relation between the wanting/liking systems, and depression has not been studied. We have previously studied these reward processing systems in healthy subjects (Petrovic et al Journal of Neuroscience 2008; Pessiglione et al Neuron 2007) in order to better undersatnd the link between depression.