Serotonin, Inhibition, and Negative Mood

In a recent study published in PLoS Computational Biology authors explored the relationship between serotonin, inhibition and negative mood. They also tried to explain contradiction
between the fact that inhibition of serotonin reuptake is the first-line treatment of depression, although serotonin itself is most strongly linked with aversive rather than appetitive outcomes and predictions through mathemetical modelling.
Full article can be found at:
http://compbiol.plosjournals.org/archive/1553-7358/4/2/pdf/10.1371_journal.pcbi.0040004-S.pdf