There’s a direct neural connection between the nipples and the oxytocinergic neurons in the brain. When Barry Komisaruk, of Rutgers University, and Stuart Brody imaged the brains of women stimulating themselves in various ways, they found that stimulating the nipples activated the brain in much the same way as stimulating the cervix. They speculated that, as it does in rodents, this kind of stimulation releases oxytocin from the PVN.
