The human brain, in very simplistic terms, has two parts – the neocortex which is located in front of the head and which receives, processes and stores information for decision making and for remembering.
The other part is the limbic system whose function is to control all the automatic systems of the body and the emotions. It also controls the survival responses, i.e. in a threatening situation, it tells you to adopt “fight or flight” responses, i.e., either to defend yourself or run away from the situation.
Drugs and alcohol program the limbic system to avoid uncomfortable situations instead of making healthy responses to resolve the associated stress and the Cortex protects such faulty behavior pattern by a filtering process called denial. The result is the addictive brain.
A communication system exists within the brain whereby the information is received and processed. The individual brain cells or neurons communicate with one another through neurotransmitters or biological messengers. Psychoactive drugs change the normal pattern of communication in two ways: