Brain, Disorders of the

I

Introduction

Brain, Disorders of the, problems with brain function that may arise through birth defects, disease, or damage to the brain resulting from stroke or physical injury. The brain controls movement, coordination, perception, and speech, as well as directing many basic bodily functions; it is where cognition takes place, and is the seat of consciousness (which, according to many scientists and philosophers, is purely a product of brain function—the relation between them is not yet understood). Damage to the brain, depending on its nature, can therefore manifest itself in forms ranging from mild difficulty in performing certain types of activity to specific and sometimes bizarre incapacities (such as mistaking objects for other objects, most famously recorded by the psychologist Oliver Sacks in his book, The Man who Mistook his Wife for a Hat), to complete personality change, paralysis, and other overall losses in physical function and cognitive ability. The brain is, however, in every sense a remarkable organ, with great capacities for regeneration and repair.

Brain disorders in newborn babies may be the result of genetic disorders, or problems during development, or they may arise from difficulties, particularly lack of oxygen, during the birth process itself. This article focuses on disorders arising later in life, as a result of injury or disease.

Much of our understanding of disorders of the brain has been obtained through studies conducted on brain-damaged patients in fields such as neuropsychology and, more recently, cognitive psychology. Such studies, often on patients with very specific, localized damage to the brain, help to find ways of curing or at any rate alleviating the problem for the patients themselves, while also improving our understanding of the nature of brain function.

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Brain Damage

Brain cells can die for a number of reasons. Various harmful substances in the environment can kill cells in the brain. After the age of 21 or so, it is thought that thousands of brain cells may be lost naturally each day through spontaneous cell turnover, though even if this may be the case, the effect on brain function is negligible, even after many years. However, there are various diseases, such as Parkinson’s disease, Alzheimer’s disease, and brain tumours, which greatly increase the rate of cell death in the brain.

Cells may also die as the result of injury to the head, for example in a road traffic accident, or as a result of decreased blood supply to the brain tissues in the case of a stroke. Sometimes surgeons have to remove brain tissue when removing a tumour, although in such cases great effort is taken to ensure it will not lead to serious disabilities for the patient.

When brain cells die in a certain area of the brain, disturbances appear in the parts of the body normally controlled by that part of the brain. When many cells die throughout the brain, there is an associated dementia (loss of brain function) with impairments to memory, personality, and intellect. This can lead to a variety of problems such as social withdrawal, mood changes, anxiety, forgetfulness, and personal neglect. The commonest cause of dementia is Alzheimer’s disease.

In cases where brain cells die in a particular area of the brain there tends to be a more restricted loss of function. The exact nature of the loss of function depends on the precise area of the brain that has been affected. Because the brain is a highly complex and interconnected organ, it is therefore difficult to pinpoint areas as being solely involved in a particular function. However, it is possible to say that patients with cell death in particular areas are more likely to have a certain group of problems, than if the damage had been in a different area.

In Parkinson’s disease, for example, a particular type of cell in the brain dies and this leads to certain problems such as uncontrollable shaking. Cells using the neurotransmitter dopamine in the basal ganglia and other areas die, and this results in patients experiencing tremors when they are resting, being slow in their movements, and having difficulties in starting and stopping a movement. Problems gradually develop in the muscles controlling the fingers, hands, arms, and trunk.

Drugs, such as Levadopa, that help replace the lost dopamine in the brain, can temporarily alleviate the symptoms. However, as they do not replace the lost cells, they can only work for a short period at a time, and therefore cannot cure Parkinson’s disease.

Certain other chemicals that act on cells in the brain have been shown to alleviate some of the symptoms in certain psychiatric disorders, such as anxiety and depression. For example, drugs that raise the concentration of serotonin in the brain can alleviate some of the symptoms of certain types of depression. As with all medicinal drugs, these drugs have to be very carefully monitored as they also act in other ways that can produce unwanted side effects.

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Speech Problems

These are commonly associated with damage to certain areas in the left temporal and left frontal lobes. Defects of language, known as aphasia, can be seen in any combination of the following: speech production, speech understanding, reading, and writing. These defects are associated with the areas of the brain that control the movements of the mouth or hand, and with areas that are responsible for other aspects of speech, such as comprehension. Some patients have considerably impaired speech production, although their ability to understand speech is relatively normal. Their speech is slow and awkward and they have difficulty in finding the right word to use in a particular context. This is referred to as Broca’s aphasia (see Paul Broca).

Patients with Wernicke’s aphasia are able to produce speech fluently and quickly with normal intonation (rising and falling pitch, such as in a question); however, it is often impossible to understand what they are saying. They find it hard to repeat sentences and frequently add irrelevant words and phrases. Their most obvious problem is that they have severely impaired understanding of speech.

Patients with both a problem in expressing themselves and a problem in understanding speech are classified as having global aphasia. It is the commonest form of aphasia, and develops after a severe stroke affecting the left hemisphere.

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Visual Problems

Damage in nerves in the occipital cortex leads to an associated deficit in vision. Since the occipital lobe is organized topographically, if a particular area is damaged it tends to result in a blindness in the associated area of the field of vision. If the right occipital cortex is severely damaged, then the patient will not be able to see anything on the left. Despite damage to the occipital cortex, some patients, although they are unable consciously to “see” an object in the particular area of their field of vision that is damaged, can nevertheless, when told to do so, point to a light flash in the blind area with remarkable accuracy. They can perform this pointing task despite saying that they cannot see anything, as although almost all the information from the retina goes to the occipital lobe, a small amount of information goes to other areas in the brain such as the superior colliculi of the midbrain. It is these areas that are thought to be responsible for this ability, which is sometimes called “blindsight”.