Scientist Solutions - Human emotion.

This is my understanding of neurotransmitter systems and their corresponding emotions - but be forewarned: the brain is staggeringly complex, and defining the exact neural correlates of phenomena like emotion or consciousness isn't really possible. What follows is just my current understanding - it could turn out that I am completely off the mark. But that aside, I think most of this is factually correct. SOrry its so long I got carried away.

The main neurochemical systems involved in emotion (that I know of) are serotonin, opiates, oxytocin, and vasopressin.

serotonin seems to be involved aggression and affect. For example, people with anger managment problems often benefit from treatment with SSRI's (Selective Seroronin Reuptake Inhibitors). Similarly, SSRI's (fluoxetine in particular) have proven to be useful in treating affective disorders (i.e. depression). Serotonin is also involved in perception in general - hallucinogenic drugs like LSD and psilocybin (the active ingredient in 'magic mushrooms') are similar in structure to serotonin and produce their effects by mimicing its action at certain receptors.

The opiate system (specifically the mu opioid system) seems to be involved in the subjective experience of love (parental love in particular), as well as feeling good in general. I remember reading a study in which infant rats that were genetically modified to have no mu opioid receptors behaved similar to non-modified infant rats that were separated from their mother; also, the mu-opioid knockout rats also showed much greater signs of anxiety and depression when separated from their mothers. This makes sense given how many people who use hard drugs - particularly heroin, a powerful mu-opioid agonist - were abused by their parents at some point, or at least had rough childhoods marked by anxiety/depression. Also, endogenous opioids (namely endorphin, enkephlin) have been implicated in the reinforcing aspects of social bonding.

THis is purely speculative, but it is my personal hypothesis that mu opioid signaling is also involved in the positive, or euphoric aspects of love. I havn't used many drugs, but in my limited experience with opioiate agonists (hyrdocodone) I have to say it felt sort of like that sublime easygoing feeling you get when you are in a relationship that is going well. Of course the flipside to this would be opiate withdrawl, which i have never experienced, but from what I know is mediated by a neurotransmitter called cholesystekinin (CCK), which is known to induce panic when injected into humans/rats/monkeys/etc - something a bit like the degection one feels after a breakup or other traumatic social insult, perhaps... (?)

Oxytocin and vasopressin seem to be involved in social bonding and the formation of a bond between mother and infant in particular. THere is a lot of research on this subject and I'm sure you could find lots on pubmed.

Other neurotransmitters are involved in the subjective experience of emotion as well: i have no doubt dopamine, norepinephrine, GABA, glutamate, and basically every neurotransmitter are also involved at some level. I know dopamine in particular is involved in re-wiring neuron's connections such that behaviors that certain behaviors are more likely to be repeated.

sorry for the rant; i've had an interest in this subject for a while myself. there are a lot of books/scientific articles out there that could tell you a lot more than I can.

PS - beyond the realm of neurochemistry, another subject relevant to the study of human emotion is autism. Autistism is marked by an inability to understand what is going on in other people's minds. A milder form of autism, known as Asperger's syndrome, is characterized by an inability to understand the subtelties of human social interaction and a preference for logical organization. You (or anyone else with an interest in the study of human emotion) may find it worthwhile to read some personal accounts from high-functioning autistics or people with Aspgerger's syndrome.