We talk about the brain in many ways-this three-pound, electrochemical unit of some 12 billion nerve cells. The human brain has powers of recuperation from evern the mst dractic emotional shocks; it is in command of a nervous system that can send message impulses at speeds that exceed those of many fast racng cars. The brain is our control center for behavior and experience. It aids in our learning anu sets up our perceptions and dreams, our thoughts and feelings.
Higher Levels of Control
Highest brain controls in the cerebral cortex, which is divided into two hemispheres. Here we find areas related to the senses and to the principal motor areas of speech and various bodily movements. Most parts of the cortex. not specifically devoted to sensory and motor functions, serve as association areas to coordinate not only sensor) motor functions but also complex learned acts .
Evidence is beginning to show that the two cerebral hemi· spheres function in some ways as "two brains." For example. the righ, hemisphere can function independently and largely outside the awareness of the left hemisphere. It can read. learn, remember. emote. and act all by itself. The two-brain concept helps to explain how left-br«.in-damaged patients can be taught. how the right brain takes over, and vice versa. Interestingly. one half-brain can go unrewarded in a learning experience and interfere with the learning of the other half-hrain which is rewarded. Studies even show that reaction time can be different for the two hrairs. Perhaps fortunately. in the normal brain there is good coordination between the two hemispheres, giving us maximum control and balanced experiences. In a crude sense, we can think of one hemisphere as a backup system for the other and vice versa.
Intermediate Levels of Control
Below the cerebral cortex we find levels of control for such viwl functions as breo.thing and heartbeat. and for various reflex centers such as those that cause us to jump when v.'e hear a loud. sudden sound. Here also we find control in the midbrain for equilibrium. posture. and muscle tone. Also in the thalamus and hyjJothalamus we find cOlltrol centers for hunger, thirst, and sex. In these intermediate centers of control we also find sleep centers and regions that relate to aggression. Here there are centers for inhibiting emotional behavior and e',en for stopping aggressivc behavior, Within the general area of the midbrain we have centers involved in "pleasure" and "displeasure," and even centers for boredom.
Lower Levels of Control
Most elementary. but important reflex coordinations are controlled uy the spinal cord. Familiar here. of course. is the knee-jerk reflex. Here a tap on the tendon just below the kneecap causes the leg to automatically kick out.
The spinal cord, in addition to being a connecting center for some reflexes, serves as the connecting cable that conducts nerve impulse messages up to the brain centers and down from them.
Autonomic Nervous System
The automatic functions of the body are coordinated by' a motor system we call the "autonomic nervous system." This system controls heart action, blood pressure, breathing, digestions, excretion, and urination. It also relates to sweating and various functions of the stomach. Interestingly, research now underway points to the ability of some people to learn through "biofeedback" to control such vital functions as blood pressure and heartbeat. Some subjects have been trained to achieve enough relaxation to gain control of migraine headaches by controlling blood pressure within the fineries of the head. Some people have learned to control high blood pressure, and even to learn mental control over relaxation.
