The central part of the brain is called the limbic system which is responsible for our emotions, memories, etc. We mammals have the only developed limbic system, so we don't rely on instincts to help us survive in life. The hippocampus which is located on each side of the brain helps us with our long term memory and also to help us remember where things are. For example, it helps us remember where we put our keys. The amygdala is the part of our limbic system that helps us with our emotions. It also has one on each side and is particularly involved in our emotions, fear and aggression. For example, if a woman has been physically abused, she may be afraid of being in a relationship again because she thinks it could easily happen again. Even though the new guy she's talking to has never hurt a fly. The hippocampus and amygdala work hand in hand when it comes to the pleasure center of the brain. Arousal due to excess electrical stimulation is caused when a person uses an addictive drug such as heroin. You actually don't need to take drugs to stimulate the limbic system, sex will do the same. There are also reward circuits in our brain, like when we get a good grade on our test or hear something really funny, these circuits can be activated.