https://www.sciencealert.com/here-s-wha ... you-orgasm
The lateral orbitofrontal cortex becomes less active during sex. This is the part of the brain that is responsible for reason, decision making, and value judgments.
Researchers have found that genital sensory cortex, motor areas, hypothalamus, thalamus, and substantia nigra all light up during the big O
Surprisingly, the brain doesn't differentiate much between sex and other pleasurable experiences. The parts of your brain that make you feel good after indulging in dessert or winning at poker are the same areas that light up during orgasm.
The reason that some people derive sexual pleasure from experiencing pain might be related to the fact that orgasm and pain actually affect a few of the same areas of the brain.