The Brain in Health and Disease

Background Information

The development and health of a child's brain is an important factor in their ability to learn. As Richard Restak notes in the introduction of The Secret Life of the Brain, at the end of infancy, a child's brain contains many more neurons than it requires, and excess neurons are pruned away based on the most fundamental tenet on brain operation: Use it or lose it. Neuronal connections are thinned out based on experience, with unused or rarely used pathways disappearing while highly used pathways flourish. Because of this process of forming and reforming connections, young children's brains develop as experiences from their environments occur.

Our Nervous System

The nervous system in our bodies works as both the decision making and communication center. The central nervous system is made up of the brain and the spinal cord. The network of nerves outside the brain forms the peripheral nervous system. Together they control the day-to-day lives we lead. Nerves branch out from the brain and the spinal cord, a bundle of nerves running up and down the spine that operates similarly to a super highway, speeding messages to and from your brain every second.

Understanding the Brain

A human brain weighs on average three pounds and can easily be held in your hands. Rather amazing when you consider that the brain lets us think, feel, choose; it governs how we breathe, our heart rate, the ability to keep our balance. It actually contains about 100 billion neurons, a number equal to the stars in the Milky Way.

Most of what we see when we look at an intact brain is the cortex. It looks wrinkled because of its many folds. These folds increase the total surface area by three times what it would be if it was smooth. ¹ The cortex processes perceptions, thinking, and memory. This is the largest part of the brain and is associated with higher thinking and action. The cortex contains the physical structures responsible for most of what we call brainwork: cognition, mental imagery, the highly sophisticated processing of visual information, and the ability to produce and understand language. The cerebral cortex is divided into four major regions: the frontal lobe involved in decision making, reasoning, planning, parts of speech, movements, emotion, problem solving; the parietal lobe involved in sensory perception, movement, orientation, recognition; the occipital lobe involved in visual perception; and temporal lobe responsible for hearing, expression, and memory. ²

In the brain layer below the surface of the cortex, a number of other specialized structures are packed: the thalamus, an important relay station for the senses, and the hypothalamus, a meeting point between the nervous system and the endocrine system, and between emotion and physical feeling. The pituitary gland, which acts on signals from the hypothalamus, produces hormones that regulate many functions from growth to reproduction. The pons and the medulla, two major elements of the brainstem, channel nerve signals between the brain and other parts of the body, controlling vital functions such as breathing and deliberate movement.

From the perspective of child development, it is helpful to look at the brain from the inside out. The brain develops roughly from the base of the skull up and outward, beginning in an embryo as a series of bulges at one end of a neural tube. These bulges develop into the hindbrain, midbrain and forebrain - divisions common to all vertebrates. Cavities called ventricles form, one on each side of the brain; these cavities are filled with cerebrosprinal fluid, which serves as a cushion for the brain.

The brainstem, the area from the spinal cord, including the medulla, the pons, and up to the midbrain, contains structures that regulate autonomic functions, which are essential for survival and not under our conscious control. This structure is in charge of controlling vital life functions such as breathing, heart beat, and blood pressure. It can be considered the simplest part of the brain: in more primitive animals, such as reptiles, the entire brain resembles our brain stem.

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In the core of the brain, just above the brainstem, resides the limbic region, or what is called the emotional brain. It is responsible for the basic drives and emotions and the associated involuntary behavior that are important for survival: pain and pleasure, fear, anger, affection. Included in this region are the thalamus and hypothalamus, structures that deal with perception, movement and vital function. ³ The thalamus consists of two oval masses, one on each cerebral hemisphere that is joined by a bridge. Here is where the nerve cell bodies sort out information from four of the senses, sight, hearing, taste and touch. Only the sense of smell sends signals directly to the cortex as well as to the thalamus. Sensations of pain, temperature and pressure are relayed through the thalamus. The hypothalamus has a great many jobs despite its small size. It regulates body functions, such as digestion. It is the main point of interaction between the nervous system, which transmits information in the form of electrical impulses, and the endocrine systems, which brings changes through release of chemical hormones. It is the place where the brain translates emotion into physical response. Strong feelings such as fear or excitement generated in the mind from stimuli are transferred into a racing heartbeat or shallow breathing by the action of the hypothalamus.

The amygdalae, which act as fear centers and sentinels of emotional awareness, are almond-shaped and located on each temporal horn. ⁴ It is through the amydala complex that the limbic system is wired into the muscles of the face, which is where we express our emotions to each other. This is also where non-verbal information is interpreted: images, sounds, smells, but not words. The amygdale takes incoming information, compares it with past experiences, and decides the "fight or flight" response. This happens before the cortex, the thinking brain, can get involved. ⁵

An important task of the emotional brain is to integrate the environmental and bodily information gathered from our senses. ⁶ The hippocampus, another major structure of the limbic system, is in charge of consolidating recently acquired information, the processing of short term memory. It controls how memories are stored and whether or not they can be retrieved. There are three types of memory: working, or short-term memory (the breakfast menu); declarative, or long-term memory (facts and figures); and procedural, or skills memory (playing a musical instrument).

At the back of the brain is the cerebellum (little cerebrum or little brain), a knobby projection behind the base of the brain and a key participant in planning. ⁷ It is the second largest portion of the brain, exceeded only by the cerebral cortex. Although not essential for movement, your cerebellum makes your moves smooth and purposeful. The outer layer of the cerebellum receives a complex array of signals from every part of your body. Signals describing your body's position and orientation arrive via the spinal cord and several areas of the brain, including the gravity sensors in your inner ear. ⁸ The cerebellum coordinates the brain's instructions for skilled repetitive movements and for maintaining posture and balance. ⁹ It has the function of relaying impulses for movement to the spinal cord, where they pass to their designated muscle groups.

Cerebrum

The cerebrum is divided into two hemispheres and integrated by the corpus callosum. The most significant feature of the cerebrum is the outer layer, the cerebral cortex, consisting of four lobes. Each of these lobes is a specialist. The specialist areas work as a unit, integrating the contributions of each lobe. The frontal lobe carries out executive functions such as decision making, the occipital lobe is responsible for vision; the parietal lobe for analysis of sensation; the temporal lobe for hearing, understanding speech and memory.

Regions of the left side of the brain gather from and govern the right side of the body and the other way around. The left side or hemisphere generally controls the ability to read, speak, and do mathematical problems. The right hemisphere is the center of musical and artistic creation and the ability to understand shape and form.

It is as though you have three brains, the first being the non-thinking brain stem with its autonomic nervous system, maintaining your vital signs: pulse, temperature and blood pressure, those things that are checked out when you first arrive at the doctor's office. Above the basal portion of your brain is the larger, animal brain, which orchestrates your emotive, instinctual behavior. In conflicts of head versus heart, this is the "voice" of the heart. The real "heart-felt" smile originates here. And above these two areas is the evolved rational brain, the cognitive cortex.