 MacLeans idea of the ‘limbic system’ is based on the role the paleomammalian brain plays in brain function, where an individual's judgement of right and wrong stems from.MacLean had a particular influence on the role that the limbic system plays on mental health when it translates messages incorrectly, for example, how an individual can enter a state of deep distress when there is no stimuli to cause such a response, relating directly to MacLeans research into the causes of Post-Traumatic Stress Disorder.The neomammalian brain consists of the cerebral neocortex, which is found in higher mammals, especially in the human brain, and is not found in birds or reptiles.