The lowest brain, the brain stem and the cerebellum, is the oldest brain. It developed first in evolution. In simple less-evolved animals, such as reptiles, the brain stem and cerebellum dominate. For this reason it is commonly referred to as the "reptilian brain". This brain controls muscles, balance and autonomic functions, such as breathing and heartbeat. This part of the brain is active, even when you are in deep, dreamless sleep.
The middle brain developed next in evolution and so is sometimes called the mammalian brain. Paul MacLean in 1952 first coined the name "limbic system" for the middle part of the brain. It used to be commonly referred to as the rhinencephalon or "smell brain," and for good reason because the center of this system holds the olfactory bulb. Then scientists discovered through electrode stimulation that there was more to this part of the brain than smell. When this part of the brain is stimulated with a mild electrical current various emotions are produced. Fear, joy, rage, pleasure and pain could all be produced at the touch of an electrode. Not that any one emotion has been found to reside in any one place for very long, that seems to change from day to day. But as a whole area the limbic system is definitely the home of emotions. It turns out that it is also the home of affective memories.
The brain on the top telencephalon called the neocortex, cerebrum, or sometimes just the cortex cortex is the evolutionary newcomer of the three brains. The higher cognitive functions which distinguish Man from the animals are in the cortex. Although all animals also have a neocortex, it is relatively small and unimportant. For instance, a mouse without a cortex appears fairly normal, a person without a cortex is a vegetable. In Man the neocortex takes up two thirds of the total brain mass. In animals it is much smaller than the other two brains.
The cortex is divided into left and right hemispheres, the famous left and right brain. The left half of the cortex controls the right side of the body and the right side of the brain controls the left side of the body. So for instance if we move our right hand we use some part of our left brain. The particular place in the left brain can be mapped by using electrode stimulation. Scientists are now busy starting to map out the general contours of the cortex, although everyone's brain appears to be somewhat unique, and even the brain of one person changes over time..."
"The upper brain is divided into four quadrants: left brain, right brain, hind and fore-brain. The upper brain, neocortex, also produces four basic types of brain wave patterns: beta, alpha, theta and delta. The four consciousness functions seems to have a home in each of the four quadrants of the neo-cortex and brain waves types. Beta waves and the left side of the neocortex go with the sensing/waking function. Alpha waves and the hind-brain go with thinking/contemplation. Theta waves and the right brain go with feeling/dreaming, and delta in the fore brain with acting/sleeping. The four sides of the brain, and four types of brain waves, like the consciousness functions themselves which underlie them, must be balanced."