MacLean's Triune Brain and Psychiatry

Neuroscientist Paul MacLean formulated the idea of the brain being '3 brains in one" based on evolution.  His ideas in comparative neuroanatomy seem simplified today with the increased understanding of bird brain development however the concept remains a powerful basis for understanding behavioural neurology.
The triune brain consists of the reptilian complex, paleomammalian complex (limbic system), and the neomammalian complex (neocortex).  It was thought they were added sequentially however it appears from bird research the evolutionary aspect of this idea is questioned.
What remains relevant is that there are essentially three major structures to the brain, the basal ganglia.  A variety of functions are associated with the basal ganglia included activation, control of voluntary muscle, procedural learning and habits. It's associated with 'action selection'.
It is of critical importance with obsessive compulsive disorder, addiction and movement disorders.

The paleomamalian brain consists of the septum, amygdala, hypothalamus, hippocampal complex, and cingulate cortex.  This is called the Limbic System, a term introduced by Maclean who argued that these structures were associated with mamamalian emotion, reproduction and parental behaviour. today we know the limbic system to be principally related to emotional relations, family and tribal behaviour.

The Neocortex , found uniquely in high mammals, especially humans is associated with the ability for language, abstraction , planning and perception.

The functional MRI studies of cocaine use show that the frontal brain, the neo cortex are indeed associated with delayed gratification and that these centers are impaired after cocaine use for three months.

Drugs and alcohool are 'disinhibiting' with regard to structures of the brain. The ability to see sound, which is an experience of babies is what occurs with hallucinogens. Nothing 'new' but rather an uncovering of something 'very old' occurs.

Drugs and alcohol therefore do not 'add' to experience but rather 'uncover' earlier experience and cause different associations.