The Psychophysiology of Sex

General Discussion

General Discussion Roy Levin: Could I just come in about the distinction between sexual arousal and desire? You can certainly have sexual arousal without desire. There’s no question about that. I can give you one instance where you can have sexual arousal, whether you mean on the brain or in the genitals; of course, then you would have to de¤ne where the “sexual arousal” is, because a man after ejaculation has “arousal” in his penis, but he has no desire in his brain. So there’s sexual arousal without desire there, for example . I wrote some time ago that you could have sexual arousal without desire and desire without arousal and, of course, your model would say that you couldn’t have that. I’m not quite sure that there’s any real evidence for that statement. I also had a model; in fact, it was at your meeting Ellen that I put forward that there may be two types of desire, so some of what you said I believe in myself. But I ¤nd that at the moment—I think John actually wrote an article with somebody, I’ve forgotten who your coworker was—but you had trouble with sexual desire, sexual arousal, and sexual stimuli, didn’t you? You couldn’t really separate those. John Bancroft: I have a lot of trouble with sexual desire! Roy Levin: I don’t remember that review, but I thought that the patella and the Achilles tendon re®exes, and tell me if I’m wrong, are cord re®exes, they don’t go up to the brain. So is dopamine acting on the cord or is it acting on the brain? I remember I used to test re®exes as an undergraduate and what you do: you trigger the patella re®ex and then you put your hands together and you pull really hard and you get a much better re®ex, and that was, as physiologists said, because you raise the excitation level in the cord, not in the brain, and that’s why you got a much bigger re®ex. So where are these potentiations taking place? Stephanie Both: Well, you are right that we cannot state that dopamine is acting only on the brain. It also can act on the spinal cord. However , I think that the fact that we ¤nd only an effect of levodopa during sexual stimulation suggests that levodopa affected the processing of the sexual stimulus. We didn’t ¤nd an effect of dopamine in the resting state, which indicates that there was no general effect of levodopa on excitation level in the cord. 369 Roy Levin: I think you will ¤nd that a lot of people now think that there are things that are happening in the cord, didn’t you say that there were things that are happening in the cord, Kevin? Kevin McKenna: It’s de¤nitely a spinal re®ex, but the fact that it’s potentiated by watching a ¤lm indicates that the effect is happening in the brain and it’s descending and affecting that spinal re®ex. Roy Levin: Things are coming from the genitals watching the ¤lm and then . . . Kevin McKenna: I don’t think so, but the L-dopa could certainly be working in the brain and causing a descending effect. Marca Sipski: I guess, but I didn’t see that you showed that L-dopa caused the re®ex. I didn’t understand that from what you said and I had a question: is the re®ex being facilitated by sympathetic activation? Sympathetic activation increases your blood ®ow to your muscles and potentially increases re®ex responses there. What was going on with your other autonomic nervous system and what was going on with heart rate, and so forth? That’s what I’d like to know. Stephanie Both: Well, we did a couple of studies in which we measured T-re®exes during emotional stimulation. We used sexual ¤lms, but also sexual pictures that were showed for a few seconds. We found sexual pictures, in contrast to neutral pictures, to enhance T-re®exes. I think it is unlikely that the effect of exposure to a sexual picture for such a short period of time is due to an increase in blood ®ow of the muscles. So I think we may be pretty sure that we are measuring increased activity in the motor system. Marca Sipski: But could the emotional stimulation be...