Get ready, because we're about to drop some very fancy, science-y words on you. According to Chatterjee, the insula, anterior cingulate, and hypothalamus are all active when you're sexually aroused. So, what do those all do? The insula regulates your autonomic nervous system, monitoring things like heart rate, blood pressure, and sweat responses (sound familiar?) while the hypothalamus handles the secretion of hormones like prolactin and oxytocin into the bloodstream. Oh, and part of the sensory cortex also becomes engaged, because your brain wants you to feel all the feelings that are happening at the time.
Though Chatterjee notes that it's very difficult to study what happens to the brain during an orgasm, there's an interesting decrease in activity in the ventromedial prefrontal cortex, anterior cingulate, parahippocampal gyrus, and poles of the temporal lobes. Chatterjee suggests that this drop in neural activity could mean the person is in a state of fear and unable to think of either themselves or future plans. The person isn't thinking about anything in particular, and their boundaries have virtually disappeared. In other words, this could mean the brain is in a state of pure transcendence, enveloped by pleasure.
The scientific language can be a bit rough reading, but we're totally into Chatterjee's delving deeper into the science behind one of the Best. Things. Ever. (Salon)