"Transmission" by Hari Kunzru. "Her serotonin- drenched brain pulled up a sugarcoated version of Arjun, somehow less gawky than lean, less sallow than mahogany-skinned, a tender young man in more or less matching clothing, ready to be initiated into the art of love (81)."

A neurotransmitter that is involved in sleep, depression, memory, and other neurological processes. The neurotransmitter handles several short term ideas that run around in the brain.Many mind altering drugs such as MDMA, ecstasy, can affect serotonin levels to influence how the brain works. Low levels of serotonin can lead to deppression, migranes, or bipolar disorder

http://www.biopsychiatry.com/serotonin.htm