There is a lot we know about the areas of the brain and the neurotransmitters involved in sex and love. Like in many other fields of study of human behavior, digging into the details is difficult. Studies are often small, and focused on the things that CAN be measured. Brain research is often limited to proxy results, such as oxygen flow to a brain region rather than actually tracking signals. Still, the modern scientific approach has learned some very useful things about sex and love, even if the sum of the parts adds up to less than the whole.
The current state of the art is reflected in these two videos on Youtube. Helen Fisher is a prominent sex and love researcher who has written six books on the evolution, biology, and psychology of human sexuality, monogamy, adultery and divorce, gender differences in the brain, the neural chemistry of romantic love and attachment, human biologically-based personality styles, why we fall in love with one person rather than another, hooking up, friends with benefits, living together and other current trends, and the future of relationships — what she calls: slow love.
For sex, Fisher identifies testosterone and estrogen in the hypothalamus, which also produces dopamine for intense feelings of attraction similar to that of addiction. The hypothalamus also plays a key role in longer-term love by producing oxytocin and vasopressin.
In a similar vein is the second video, where in addition to Helen Fisher, Gail Saltz discusses love and neurotransmitters.
