The catnip stimulates three main areas of the cat’s brain; the olfactory bulb which processes scent, the amygdala which is involved in emotions and decisions, and the hypothalamus which is in charge of sexual response among other things. The last one helps explain why cats exposed to catnip will often roll on the ground like a female cat in heat. It’s also probably why kittens don’t usually respond to catnip until they’re sexually mature, when they’re around six months old, but not every cat does respond to catnip. Only about fifty to seventy percent of cats do. It’s genetic and scientists are still looking to identify the gene involved and learn more about what exactly is going on in the cat’s brain when it’s reacting to catnip.