It has the same type of archaic behavioural programs as snakes and lizards. This brain controls muscles, balance and autonomic functions, such as breathing and heartbeat. This part of the brain is active, even in deep sleep. It corresponds to the brain of the most mammals , and especially the earlier ones. The old mammalian brain residing in the limbic system is concerned with emotions and instincts, feeding, fighting, fleeing, and sexual behaviour.
Survival depends on avoidance of pain and repetition of pleasure.
No emotion has been found to reside in one place for very long. Physiologically, it includes the the hypothalamus, hippocampus, and amygdala. It has vast interconnections with the neocortex, so that brain functions are not either purely limbic or purely cortical but a mixture of both. MacLean claims to have found in the Limbic system a physical basis for the dogmatic and paranoid tendency, the biological basis for the tendency of thinking to be subordinate feeling, to rationalize desires. He sees a great danger in all this limbic system power.