Orgasm is for man, and perhaps even more for woman, the supreme ecstasy. Nevertheless, our knowledge of its mechanisms is sketchy. The physiological manifestations (muscular contractions, cardiac rhythm changes, blood flow, etc.) tell us little about the sensation. Orgasm is a cerebral experience.

[IMAGE: release]Recordings of brain activity taken at the moment of orgasm show no major change in electrical activity of the cerebral cortex. In Robert Heath's 1972 study, however, one subject had spikes and slow waves of high amplitude, mixed with rapid oscillations in potential, appear in the limbic system in the septum. In form, these waves resembled those found during an epilep tic seizure, with each slow wave resulting from thousands, if not millions, of elementary electrical impulses. In a female subject, the same phenomena spread to the amygdala and thalamic nuclei, but never invaded the neocortex. Heath also noted that an injection of acetylcholine into a female subject's septum provoked an intense sensation of sexual pleasure, culminating in repeated orgasm. Could dopamine, and the pleasure synapses that contain it, be involved? There is no data to support or refute this thesis.

[IMAGE: rorschach ink blot]Orgasms are accompanied by a massive discharge of oxytocin, a hormone released from the hypothalmus that acts on the mammary glands. (Stretching the vagina of a cow brings about the flow of milk.)

Orgasms are followed by higher than normal levels of endorphin-type peptides in the blood stream -- hence the abolition of pain, contented feelings, and usually agreeable change in mood that occurs. Use of opiates tends to diminish sexual activity, th e attendant artificial rise in endorphins probably being responsible. The level of endogenous opiates (those released naturally after orgasm) is a likely regulator of libido. Perhaps the level is a measure of what Sigmund Freud called, rather clumsily, "psychic energy".

In contrast to other forms of behavior, orgasms are not primarily manifested by an action clearly visible to the outside world, but are essentially a subjective sensation, experienced internally. The multiplicity of the chemical mediators involved str ikingly illustrates an immense diversity of neurons involved. The chemical makeup of the cells that participate in the sensation of orgasm is closer to a canvas by Georges Seurat than a composition by Piet Mondrian.

jean paul changeux
neuronal man
pantheon books
new york, new york
1985