Paul D. Maclean, chief of the Laboratory of Brain Evolution and Behavior at the National Institute of Mental Health, identifies three separate physiological levels of the human brain, each corresponding with a stage in our evolutionary history. According to MacLean’s triune brain theory, these three separate brains are superimposed on one another, so that while many of their functions overlap, they are all quite different in chemistry, in structure, in action, and in style. Each of the three brains has its own drives, its own memory, its own problem solving ability; each functions as a fairly autonomous brain on its own level. As MacLean points out, the human brain is hindered by a ruinous “design error”; there is insufficient communication and coordination between the “rational” neocortex and the two older levels of the brain.
Reptile Brain- The most ancient part of the brain is a combination of the spinal cord, the brain stem, and the midbrain. This system controls basic self-preservative, reproductive and life-sustaining functions; such as respiration, heart regulation, and blood circulation. It is the location of the reticular activating system (RAS), the “alarm bell of the brain,” which determines our arousal level and our state of awareness and attention. The RAS distinguishes between events that are normal and those that are out of the ordinary, and makes sure we pay attention to the new while allowing us to ignore the familiar. The RAS not only arouses us and focuses our attention, it can also inhibit brain function, causing us to fall asleep or lapse into coma.
Floating in an isolation tank has a powerful effect on the reticular activating system, causing it to put the floater into a deeply relaxed yet highly alert state of calm reverie.
Paleomammalian Brain- The next part of the brain to develop is known as the limbic system, which is situated atop the reptile brain in somewhat the manner of a hand clutching the knob of a cane. Because we share this area of the brain with other mammals(such as the rabbit, rat and horse), it has been called the paleomammalian brain. Ruling the limbic system is the hypothalamus. Known as “the brain’s brain,” this structure is the main regulator of all bodily functions, the most powerful of the brain’s emotion-causing centers, controlling those innate biological drives and processes most fundamental of survival(such as hunger, thirst, sex, maintaining body temperature) and exercising a pervasive influence over all our emotions and drives.
Recent studies by endocrinologists and other scientists show that floating has a direct and very substantial influence on the hypothalamus. Because of its powerful, rapid, and long-lasting influence on the limbic system, floating has an enormous effect on mood, emotions, control over autonomic functions, and all aspects of the mind-body interrelationship.
Neocortex- This “roof-brain” is the seat of our high-order abstract, cognitive functions: memory, judgment and intellect. It is in charge of our voluntary movements and actions.
As a number of recent studies demonstrate, the float tank experience seems to operate directly, rapidly, and dramatically to bring about increased communication and harmony between the vertical levels of the brain, and it does so without prerequisite training, instruction, practice, or arduous self-discipline.