CHAPTER 110

Brain Dysfunction

Brain damage can cause many types of dysfunction. Such dysfunction ranges from complete loss of consciousness (as occurs in a coma), to disorientation and an inability to pay attention (as occurs in delirium), to impairment of one or several of the many specific functions that contribute to conscious experience. The type and severity of brain dysfunction depend on how extensive brain damage is, where the damage is, and how quickly the disorder causing it is progressing.

Brain dysfunction may be widespread (diffuse) or limited to a specific area (localized). Diffuse dysfunction is caused by disorders that affect large areas of the brain, including the following:

Disorders that cause metabolic abnormalities, such as low levels of sugar in the blood (hypoglycemia) or low levels of oxygen in the blood (usually due to a lung or heart disorder)

Infections, such as meningitis and encephalitis

Very high or very low blood pressure

Diffuse brain dysfunction may also result from disorders that cause swelling of or put pressure on a large area of the brain, including the following:

Brain abscesses

Large brain tumors

Severe or blunt head injuries

Certain drugs, such as opioids (narcotics), some sedatives (such as benzodiazepines and barbiturates), and antidepressants may cause diffuse brain dysfunction if people are sensitive to their effects (as older people are) or if the level of drug in the blood is too high.

Localized brain dysfunction is caused by disorders that affect a specific area of the brain, including the following:

Brain tumors that affect a relatively small area of the brain

Disorders that reduce the blood (and thus the oxygen) supply to a specific area, such as a stroke

Penetrating head injuries that affect only a relatively small area of the brain

Certain types of seizure disorders

Diffuse damage tends to affect consciousness, making people difficult to arouse (causing stupor) or impossible to arouse (causing coma). Localized damage tends to affect specific functions. However, the severity of brain dysfunction depends on the extent of brain damage as well as the location. When the cerebral cortex (the outer layer of the cerebrum, the largest part of the brain) is damaged, the degree of dysfunction is proportionate to the extent of the damage: The more extensive the damage, the more severe the dysfunction is likely to be. However, when the brain stem (which regulates critical body functions and levels of consciousness) is damaged, a relatively small amount of damage may cause complete loss of consciousness and even death.

Disorders that progress rapidly are more likely to cause noticeable symptoms of brain dysfunction than disorders that progress slowly—for example, a fast-growing brain tumor versus a slow-growing one. The brain compensates for gradual changes more easily than for rapid changes.

Three characteristics of the brain help it compensate and recover after it has been damaged:

Redundancy: More than one area can perform the same function.

Plasticity: Nerve cells in certain areas can change so that they can perform a different function.

Adaptation: Areas with somewhat overlapping functions can sometimes compensate for lost functions.

Consequently, undamaged areas of the brain sometimes take over functions performed by a damaged area, contributing to recovery. However, as people age, the brain becomes less able to shift functions from one area to another. Some functions, such as vision, cannot be performed by other areas of the brain. Direct damage to areas that control such functions may have permanent effects.

Dysfunction by Location

Because different areas of the brain control specific functions (see also page 624), the location of brain damage determines the type of dysfunction that results. Which side of the brain is affected is also important because the functions of the two halves of the cerebrum (cerebral hemispheres) are not identical. Some functions of the brain are performed exclusively by one hemisphere. For example, movement and sensation on one side of the body are controlled by the hemisphere on the opposite side. Other functions are performed predominantly by one hemisphere, which is said to be dominant for that function. For example, the left hemisphere predominantly controls language in most people. This characteristic is called left-hemisphere language dominance. Damage to only one hemisphere of the brain may cause complete loss of such functions. However, most functions (such as memory) require coordination of several areas in both hemispheres. For such functions to be completely lost, both hemispheres must be damaged.

When Specific Areas of the Brain Are Damaged

Different areas of the brain control specific functions. Consequently, where the brain is damaged determines which function is lost.

Specific patterns of dysfunction can be related to the area of the brain that has been damaged.

Frontal Lobe Damage: Generally, damage to the frontal lobes causes loss of the ability to solve problems and to plan and initiate actions, such as crossing the street or answering a complex question. But some specific impairments vary depending on which part of the frontal lobe is damaged.

If the back part of the frontal lobe (which controls voluntary movements) is damaged, weakness or paralysis can result. Because each side of the brain controls movement of the opposite side of the body, damage to the left hemisphere causes weakness on the right side of the body, and vice versa.

If the middle part is damaged, the ability to move the eyes and to perform complex movements in the correct sequence may be impaired. People may have difficulty expressing themselves in words—an impairment called Broca’s (expressive) aphasia (see page 680).

If the front part is damaged, any of the following may result:

Impaired concentration

Reduced fluency of speech

Apathy

Inattentiveness

Delayed responses to questions

A striking lack of inhibition, including socially inappropriate behavior

People who lose their inhibitions may be inappropriately euphoric or depressed, excessively argumentative or passive, and vulgar. They may show no regard for the consequences of their behavior. They may also repeat what they say.

Parietal Lobe Damage: Damage to the front part of the parietal lobe on one side causes numbness and impairs sensation on the opposite side of the body. Affected people have difficulty identifying a sensation’s location and type (pain, heat, cold, or vibration).

If the back part is damaged, people cannot tell the right from the left side (called right-left disorientation) and have problems with calculations and drawing.

If the right parietal lobe is damaged, people may be unable to do simple skilled tasks, such as combing their hair or dressing—called apraxia.

If the parietal lobe is suddenly damaged, people may ignore the serious nature of their disorder and neglect the side of the body opposite the injury or even deny its existence. Such people may become confused or delirious and unable to dress themselves or to do other ordinary tasks.

Temporal Lobe Damage: If the right temporal lobe is damaged, memory for sounds and shapes tends to be impaired. If the left temporal lobe is damaged in people with left-hemisphere language dominance, memory for words can be drastically impaired, as can the ability to understand language—an impairment called Wernicke’s (receptive) aphasia. Sometimes damage to part of the temporal lobe can cause personality changes such as humorlessness, extreme religiosity, and loss of libido.

Did You Know…

Other areas of the brain can sometimes adapt and take over the functions of a damaged area.

Occipital Lobe Damage: The occipital lobe contains the main center for processing visual information. If the occipital lobe on both sides of the brain is damaged, people cannot see, even though the eyes themselves are functioning normally. This disorder is called cortical blindness. Some people with cortical blindness are unaware that they cannot see. If the front part is damaged, people have difficulty recognizing familiar objects and faces and accurately interpreting what they see.

Specific Types of Dysfunction

Many functions of the brain are performed by several areas of the brain working together (networks), not by a single area in the brain. Damage to these networks can cause aphasia, apraxia, agnosia, or amnesia.

Usually, doctors can diagnose the type of dysfunction by examining the person. They ask questions designed to evaluate specific brain functions. Imaging tests, such as computed tomography (CT) and magnetic resonance imaging (MRI), are usually needed to identify the cause of the damage.

APHASIA

Aphasia is partial or complete loss of the ability to express or understand spoken or written language. It results from damage to the areas of the brain that control language.

Testing a Person With Aphasia

Doctors can usually identify the type of aphasia based on how the person answers a few questions.

Broca’s aphasia: Answers to questions are given hesitantly but are sensible.

Question: “What is this a picture of?” (dog barking)

Answer: “D—d—d—dg, eh, no…d-d… damn…p-p-pet, yeah, yeah, pet, pet, pet…b—b—…makes noise.”

Wernicke’s aphasia: Answers to questions are given fluently but are nonsensical.

Question: “How are you today?”

Answer: “When? Easy for my river runs black boxes wizzel abata on when boobles come.”

Conduction aphasia: Language is understood and spontaneous speech is unaffected, but sentences spoken or written by others cannot be repeated.

Question: Repeat the following: “No ifs, ands, or buts about it.”

Answer: “No nifs nand nor but… “

Anomia: Naming things is difficult.

Question: “What is this?” (pointing to a jacket lapel, watch band, or pen)

Answer: “What you wear, thing for time, you write with it.”

People may have difficulty reading, writing, speaking, understanding, or repeating language.

Doctors can usually identify the problem by asking the person questions.

Speech therapy can help many people with aphasia.

In most people, part of the left temporal lobe called Wernicke’s area and part of the left frontal lobe called Broca’s area control language function. Damage to any part of these small areas interferes with at least some aspect of language function. Usually, writing and speech are affected similarly. Aphasia is the most common language disorder among older people.

Aphasia usually results from disorders that do not cause progressive damage, such as a stroke, some tumors, head injury, or brain infection. In such cases, aphasia does not worsen. But if it results from a progressive disorder (such as an enlarging brain tumor), aphasia can progressively worsen.

People with aphasia have difficulty expressing or understanding language. But the nature and degree of the difficulty vary. The variety reflects the complex nature of language function. For example, aphasia may involve loss of only the ability to comprehend written words (alexia) or the ability to recall or say the names of objects (anomia). Some people with anomia cannot remember the right word at all. Others have a word in mind but cannot say it. Most people with aphasia have anomia. Or aphasia may involve only the inability to repeat words, phrases, or sentences (conduction aphasia). People with conduction aphasia understand spoken and written words and can speak fluently.

Most people with aphasia have more than one type of aphasia. One type is often more severe than the others.

Wernicke’s (Receptive) Aphasia: If Wernicke’s area is damaged, people have difficulty understanding spoken and written language. They usually speak fluently and with a natural rhythm, but the sentences come out as garbled, confused strings of words (sometimes referred to as word salad). They may not know that they are speaking nonsense.

Broca’s (Expressive) Aphasia: If Broca’s area is damaged, people may mostly understand the meaning of words and know how they want to respond. However, they have difficulty finding the words to say. Their words are forced out slowly and with great effort, sometimes interrupted by expletives. Most affected people are also unable to write words.

Complete (Global) Aphasia: If the left temporal and frontal lobes are damaged, people may be almost entirely unable to understand, speak, or write language. People may be able to utter expletives because the right side of the brain, which is more involved in emotions, is not damaged.

Treatment

Speech therapists can help people who develop aphasia after brain damage due to disorders that do not cause progressive damage (see page 56). Therapy is usually started as soon as people are able to participate, but it is helpful even when started much later. Usually, most recovery of language skills occurs during the first 3 months, but it can continue for more than 6 months.

Family members and other people who care for a person with aphasia can become frustrated. Remembering that aphasia is a physical disorder and that a person has little control over it can help.

DYSARTHRIA

Dysarthria is loss of the ability to articulate words normally.

Although dysarthria seems to be a language problem, it is really a muscular (motor) problem. It may be caused by damage to the brain stem or to the nerve fibers that connect the outer layer of the cerebrum (cerebral cortex) to the brain stem. The brain stem controls the muscles used in breathing (which help make sounds). The nerve fibers relay information needed to control and coordinate the muscles used to produce speech, including those of the lips, tongue, palate, and vocal cords.

People who have dysarthria produce sounds that approximate what they mean and that are in the correct order. Speech may be jerky, staccato, breathy, irregular, imprecise, or monotonous, depending on where the damage is. Because the ability to understand and use language is not usually affected, most people with dysarthria can read and write normally.

Speech therapy helps some people with dysarthria (see page 56).

APRAXIA

Apraxia is loss of the ability to do tasks that require remembering patterns or sequences of movements.

Apraxia, an uncommon disability, is usually caused by damage to the parietal or frontal lobes. People with apraxia cannot remember the sequence of movements needed to complete simple skilled or complex tasks. For example, buttoning a button, which consists of a series of steps, may be impossible, even though the hands are physically capable of doing the task. People with verbal (speech) apraxia cannot produce the basic sound units of speech because they cannot initiate, coordinate, or sequence the muscle movements needed to talk.

Some forms of apraxia affect only particular tasks. For example, people may lose the ability to do any one of the following: draw a picture, write a note, button a jacket, tie a shoelace, pick up a telephone receiver, or play a musical instrument.

Occupational therapy (see page 50) may help some people with apraxia learn to compensate for their losses.

AGNOSIA

Agnosia is loss of the ability to associate objects with their usual role or function.

Agnosia is relatively rare. Agnosia is caused by dysfunction in the parietal, temporal, or occipital lobes of the brain, where memories of the uses and importance of familiar objects, sights, and sounds are stored. Agnosia often develops suddenly after a head injury or stroke.

Symptoms vary depending on the lobe that is damaged:

Parietal lobe: This type of damage usually results from a stroke. People have difficulty identifying a familiar object (such as a key or safety pin) that is placed in the hand on the side of the body opposite the damage. However, when they look at the object, they immediately recognize and can identify it.

Occipital lobe: People cannot recognize familiar faces or common objects, such as a spoon or a pencil, even though they can see these things. This impairment is called visual agnosia.

Temporal lobe: People may be unable to recognize sounds even though they can hear sounds. This impairment is called auditory agnosia.

Thanks for the Memories

Amnesia is a popular theme for many movies and television shows. Characters often appear with no identity and no memories of the past. They are essentially starting over, but they, for the most part, are fully equipped mentally to do so. However, this cinematic portrayal has little in common with the reality of amnesia.

In the movies: The amnesia may be unrelated to any abnormality or injury of the brain. People just forget. The reason may be unclear. Sometimes sleep seems to wipe the memory clean of the previous day’s events—an improbable scenario but full of comic possibility. Or the cause may be a blow to the head, a head injury in a crash of some sort, or a psychologic trauma, such as witnessing a murder or being raped. Or memories may be removed by a special erasing device, as used in Men in Black or Eternal Sunshine of the Spotless Mind.

In reality: Amnesia usually has less glamorous causes, such as a brain infection, alcoholism, a stroke, drugs, a brain tumor, or brain surgery. Psychologic trauma occasionally causes amnesia—a disorder called dissociative amnesia. However, psychologic trauma often has the opposite effect on memory loss. People cannot forget what happened to them. They frequently replay and relive the traumatic event, even though they would rather forget it.

In the movies: People with amnesia have few if any problems with everyday activities. They may readily get a new job and make new (or new-old) friends.

In reality: Most people have great difficulty learning and retaining new information (because the brain has been damaged). As a result, they struggle with everyday activities. People have difficulty remembering names and where they are going and why. These problems cause frustration, and people with amnesia often feel very confused and get lost.

In the movies: People often go through a complete personality change. Values and behaviors are transformed. Bad people become good.

In reality: Amnesia affects personality or identity only rarely, when the specific areas of the brain that controls these functions malfunction.

In the movies: People with amnesia due a trauma have stored memories of the trauma, intact and accurate, deep in their unconscious. With the right trigger, they can replay the memories of the trauma like a video camera.

In reality: The way the brain recalls memories is dynamic. When people remember an event, they reconstruct it, pulling bits from different places in the brain. No memory, traumatic or otherwise, is ever frozen and immune from reconstruction over time.

In the movies: Amnesia can be cured mechanically. That is, amnesia caused by a blow to the head can often be reversed by another blow. Or amnesia, regardless of its cause, can be cured by looking at a familiar object or by being hypnotized.

In reality: Most of these cures are dubious. A second blow to the head is more likely to cause further damage. Hypnosis is useful only when the cause of amnesia is a traumatic event. Then, when done gently and carefully, it is often successful. Treatment and its chances of success depend on the cause.

In the movies: Memories are not really lost, just temporarily inaccessible.

In reality: Whether memories can be recovered depends on the severity and cause of the damage. Often, the damage is not severe, or the cause is temporary. In such cases, the amnesia often lasts for only minutes or hours, and most people recover their memory without treatment. However, when damage is substantial, memory often cannot be recovered.

Some people with agnosia improve or recover spontaneously. Others must learn to cope with their strange disability. No specific treatment exists.

AMNESIA

Amnesia is total or partial loss of the ability to recall experiences or events that happened in the preceding few seconds, in the preceding few days, or further back in time.

Memory loss may involve events that occurred just before the cause of the amnesia (retrograde amnesia) or just after (anterograde amnesia). How far back in time memories are lost varies from a few seconds before the amnesia occurred to a few days, to further back in time, affecting remote (long-term) memories.

The brain’s mechanisms for storing information and recalling it from memory are located primarily in the temporal and frontal lobes, but many areas of the brain are involved in memory. Emotions originating from the limbic system can influence the storing of memories and their retrieval. The limbic system includes part of the cerebrum and some structures deep within the brain. Areas that are responsible for alertness and awareness in the brain stem also contribute to memory. Because memory involves many interwoven brain functions, virtually any type of brain damage can result in amnesia.

How amnesia is caused is only partly understood. It may result from a head injury, disorders that reduce the supply of blood or nutrients to the brain (including strokes, seizures, and migraines), brain infection (encephalitis), brain tumors, alcoholism, severe mental stress, or use of certain drugs (such as amphotericin B or lithium).

Depending on the severity of the damage, most amnesias last for only minutes or hours, and most people recover their memory without treatment. However, if brain damage is severe, remote memories can be lost forever. A few people are never able form new memories.

Transient Global Amnesia: People suddenly but temporarily lose the ability to store new memories and to recall events that happened during the previous few hours to the previous few years. As a result, people become forgetful and confused about time, place, and sometimes the identity of other people.

This type of amnesia may be caused by temporary blockage of the arteries that supply blood to the temporal lobe. Such blockages usually result from atherosclerosis, especially in older people. Transient global amnesia may also be caused by a seizure originating in the temporal lobe. Often, the cause is unknown. In young adults, migraine headaches, which temporarily reduce blood flow to the brain, may cause transient global amnesia.

Most people with transient global amnesia have only one episode in a lifetime. About 10% have repeated episodes. Episodes usually last from 30 minutes to about 12 hours. After an episode, the confusion usually clears quickly, and total recovery is the rule, although people may not remember what happened during the episode.

Treatment depends on the cause.

Wernicke-Korsakoff Syndrome: This unusual form of amnesia may develop in alcoholics and other malnourished people, usually because of a deficiency of thiamin (vitamin B1). The syndrome combines two disorders: an acute confusional state (Wernicke’s encephalopathy—see page 2088) and an amnesia (Korsakoff’s syndrome—see page 2089). Korsakoff’s syndrome develops in about 80% of people with untreated Wernicke’s encephalopathy.

Wernicke’s encephalopathy causes loss of balance, drowsiness, a tendency to stagger, and eye movement problems in addition to confusion.

Korsakoff’s syndrome may initially cause severe memory loss for recent events. More remote memory seems to be less impaired. Thus, people may be able to interact socially and converse coherently even though they cannot remember anything that happened in the preceding few days, months, or years or even in the preceding few minutes. They tend to make things up (confabulate) rather than admit that they cannot remember.

Treatment consists of thiamin and fluids given intravenously. Such treatment can correct Wernicke’s encephalopathy, although recovery is usually incomplete. If untreated, Wernicke’s encephalopathy can be fatal, but death rarely results in developed countries.