Section 6. Brain, Spinal Cord, and Nerve Disorders

Chapter 82. Brain Dysfunction

Topics: Introduction | Dysfunction by Location | Specific Types of Dysfunction

Dysfunction by Location

Because different areas of the brain control specific functions (see Section 6, Chapter 76), the location of the 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. For example, the left hemisphere is predominantly responsible for language. Damage to only one hemisphere of the brain may cause complete loss of such functions. However, other functions, such as memory, are performed by both hemispheres, so that complete loss of a function requires damage to both hemispheres.

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.

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 predominantly 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 of the frontal lobe is damaged, the ability to move the eyes, to perform complex movements in the correct sequence, or to say words may be impaired. Impairment of the ability to say words is called expressive aphasia (see Section 6, Chapter 82).

If the front part of the frontal lobe is damaged, the result may be impaired concentration and reduced fluency of speech; apathy, inattentiveness, and delayed responses to questions; or 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 disregard 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). Damage to the back part of the parietal lobe causes right-left disorientation and problems with calculations and drawing. Damage to the right parietal lobe can cause apraxia--the inability to perform simple skilled tasks, such as brushing the hair or dressing. Sudden damage to the parietal lobe can cause people to ignore the serious nature of their disorder and even neglect or deny the existence of the side of the body opposite the injury. Such people may become confused or delirious and unable to dress themselves or to perform other ordinary tasks.

Temporal Lobe Damage: Damage to the right temporal lobe tends to impair memory for sounds and shapes. Damage to the left temporal lobe can drastically impair memory for words as well as the ability to understand language (causing receptive aphasia). Sometimes damage to a part of the temporal lobe can cause personality changes such as humorlessness, extreme religiosity, and loss of libido.

Occipital Lobe Damage: The occipital lobe contains the main center for processing visual information. When the occipital lobe on both sides of the brain is damaged, cortical blindness results. People with this disorder cannot see, even though the eyes themselves are functioning normally. Some people with cortical blindness are unaware that they cannot see. Damage to the front part of the occipital lobe can impair the ability to recognize familiar objects and faces and to accurately interpret what is seen.