Serotonin slows aggression

Serotonin is not just a 'good' hormone, it has apparently also inhibit
aggression. Artificial serotonin deficiency led to emotional loss of
control in subjects such as brain researchers report.

Scientists at the University of Cambridge have as part of a study
participant put on serotonin-deficient diet and compared them via
brain scan with a control group. The subjects were instructed to
classify angry, fearful or neutral portraits as male or female, in
fact, the researchers examined, however, something else: namely, the
reaction to the angry expression on their faces.
the study

"Effects of Acute Tryptophan Depletion on prefrontal-amygdala
connectivity While viewing facial signals of aggression," Biological
Psychiatry (doi: 10.1016/j.biopsych.2011.07.033).

As a team led by Luca Passamonti in the journal "Biological
Psychiatry", writes in the diet group, the communication between the
amygdala and the prefrontal cortex was reduced. The former is involved
in the production of emotions, the latter in its control. The effect
was most pronounced among those who had, according to previous
interviews with violent tendencies. Luca Passamontis conclusion: "It
was as if the voice of reason silenced."