A 'New Type of Depression' May Have Just Been Discovered, Scientists SayResearchers from Hiroshima University (HU), Japan, have proposed a*new explanation for the biological mechanism behind depression, according to*a study published in the journal Neuroscience. Currently, most treatments for depression are based on one hypothesis of how the mental disorder arises. This explanation, known as the monoamine hypothesis, states that depleted levels of the chemicals serotonin, norepinephrine and/or dopamine in the brainówhich are all different types of monoaminesóresult in depressive symptoms.