This isn’t strictly a “sex paper,” but I have found it invaluable: Berridge’s “Pleasures of the Brain” (PDF) in “Brain and Cognition.”
This is a loooong paper – 19 pages of text with nearly 5 pages of references, holy crap – and covers a wide body of research, so I’ll just give an overview of the stuff I find most useful.
Berridge’s model of positive affect as “emotion” aims to understand the “core processing” of positive affect. A key feature of this “core processing” idea is a distinction between “liking” incentives an “wanting” incentives. That an organism can go, “Ooh, I want that!” without also going, “Ooh, I like that!” is in some ways a radical way of thinking about motivation. You can see how this might have some important implications for the study of sex and sexual behavior, right? “Wanting” here is shorthand for (“incentive salience.”)
Various portions of the hypothalamus, which constitute what is generally called, by journalists who need a shortcut, “the pleasure centers of the brain,” generate self-stimulation behavior in rats. That is, stick an electrode right into their brain and once they figure out that Behavior X results in a jolt right to that brain area, they’ll do Behavior X over and over.
Because they like that jolt? Or because they want it?
Because they want it. And you can want without liking.
In the rare direct mention of sex, Berridge describes a case from the 60s of a man who had a thing planted in his brain to stimulate these “pleasure centers,” as treatment for severe depression and also homosexuality (at that time, being gay was considered a mental disorder by psychiatrists):
The stimulation evoked strong sexual arousal and interest. But it did not produce pleasurable sexual orgasm, not even after a thousand consecutive stimulations, unless B-19 was allowed to simultaneously masturbate (or to copulate with a prostitute who was persuaded to provide therapy on one occasion, in what must be one of the most astounding accounts ever published in scientific literature)…The stimulation did not serve as a hedonic sexual pleasure, and did not substitute for sexual acts. What it did instead was to make him want to do sexual acts, and to make a wider array of stimuli sexually arousing (such as heterosexual pornographic films that ordinarily were unexciting to him).
So next time you hear “pleasure centers of the brain,” be careful they don’t actually mean “‘wanting’ centers of the brain.”
The actual ‘liking’ centers of the brain appear to be the nucleus accumbens shell, the ventral pallidum, and the brainstem parabrachial nucleus. (Say that 5 times fast.) These are brain areas that, in different ways, are associated with actual PLEASURE (“liking”) as well as wanting.
So. Here is the important summary: Just because you want it, doesn’t mean it feels good.
And I’m going to add: just because it feels good, doesn’t mean you want it. That’s not in this paper; it’s elsewhere.
BTW, yes. When I first read this paper my brain exploded.