The Subcortex

The Subcortex is located below the cerebral cortex and completely covered by it. It can be divided into three general areas: (1) Brainstem or hindbrain; (2) Midbrain; and (3) forebrain.

A person can loose large portions of the cerebrum and still survive. As a matter of fact, If damage is limited to the less crucial areas of the cortex, little visible change may take place. This is not so of the subcortex. The areas here are so basic to normal functioning that damage may endanger a person's life.

1. The Brainstem or Hindbrain. As the spinal cord enters the skull to join the brain, it widens into the brainstem, or hindbrain, consisting mainly of:

The medulla = contains centers important for the reflex control of vital life functions, including heart rate, breathing, swallowing, and the like. Various drugs, diseases, or injuries can interrupt the vital functions of the medulla enough to end or endanger life.

The Reticular Formation = In a space within the medulla and brainstem is a network of fibers and cell bodies called the reticular formation (RF).


Functions:
1st. It acts as a kind of central clearinghouse for most information coming to and from the brain.

2nd. it gives priority to some incoming messages, while excluding others. In this way the RF affects attention. Without the RF we would be overwhelmed with useless information from the environment.

3rd. and perhaps most important, the reticular formation is responsible for alertness and wakefulness. Procedure: Incoming messages from the sense organs branch into the reticular formation. There they form a reticular activating system (RAS). The RAS bombards the cortex with stimulation, keeping it active and alert. Destroying the RAS causes animals to enter a coma resembling sleep.

The cerebellum= looks like a miniature cerebral cortex, and it lies at the base of the brain. It is closely connected to many areas in the brain and spinal cord. It primarily regulates posture, muscle tone, and muscular coordination. May also play a role in some types of memory. Simple tasks like walking, running, or playing catch are impossible without an intact cerebellum. Spinocerebellar degeneration, a crippling disease, begins with tremor, dizziness, and muscular weakness. Soon a person over-reaches and under-reaches for objects--and eventually have difficulty standing, walking or even feeding themselves.

2. The Midbrain.

3. The Forebrain. Two of the most important parts of the body, like gemstones of nerve tissue, lie buried deep within the center of the brain: The thalamus and an area just below it called the hypothalamus are part of the forebrain.

The Thalamus. A football-shaped structure that acts as a final "switching station" for sensory messages on their way to the cortex. Information from vision, hearing, taste, and touch relay through the thalamus. Sensory messages undergo initial analysis there as well. Injury to even small areas of the thalamus can cause deafness, blindness, or loss of any other sense, except smell.

The Hypothalamus. About the size of a thumbnail. Small as it may be, the hypothalamus is a kind of master control center for emotion and many basic motives. It affects behaviors as diverse as sex, rage, temperature control, hormone release, eating and drinking, sleep, waking, and emotion. The hypothalmus is a sort of "crossroads" that connects with many other areas of the cortex and subcortex. As such, it acts as a "final path" for many kinds of behavior leaving the brain. You might think of the hypothalamus as the last area of the brain where many behaviors are organized or "decided on."

The Limbic System. The hypothalamus, parts of the thalamus, and several structures buried within the cortex form the limbic system--a kind of "primitive core" of the brain. It has an unmistakable role in producing emotion and motivated behavior. Rage, fear, sexual response, and other instances of intense arousal can be obtained from various points in the limbic system. During evolution, the limbic system was the earliest layer of the forebrain to develop. In lower, relatively primitive animals, the limbic system helps organize the appropriate response to stimuli: feeding, fleeing, fighting, or reproduction. In humans, the link to emotion remains. However, some parts of the limbic system have taken on additional, higher-level functions.

The Hippocampus, found at the core of the temporal lobes, is one part of the limbic system that appears to be important for forming lasting memories. A link between the hippocampus and memory may explain why stimulating the temporal lobes can produce memory-like or dreamlike experiences.

A finding in psychobiology was that animals will learn to press a lever to deliver electrical stimulation to the limbic system as a reward. Many additional areas of the limbic system have been shown to act as reward, or "pleasure," pathways in the brain. Many are found in the hypothalamus, where they overlap with areas associated with drives such as thirst, sex, and hunger. Punishment, or "aversive," areas have also been found in the limbic system. When these areas are stimulated, animals show discomfort and will work to turn off the stimulation. Since a great deal of human and animal behavior is directed by seeking pleasure and avoiding pain, these discoveries continue to fascinate psychologists.