Eleanor Johnson, age 15, of Reno, Nev., for her question:
WHAT CAUSES LEARNING DISABILITIES?
Learning disabilities are disorders that damage a child's ability to learn. Children with learning disabilities may have average or above average intelligence and they may also have normal hearing and vision. But they cannot use information transmitted by the senses to the brain as accurately as most other children can. As a result, they do poorly in school.
Doctors cannot always discover the specific cause of a child's learning disability. But scientists believe that most learning disabilities result from minor damage to the brain or to major nerves leading to the brain.
Illness or poor nutrition in a pregnant woman can injure the brain tissue and nervous system of her unborn child. Also brain damage can occur at birth if the baby's brain does not receive enough oxygen.
Sometimes a child may inherit a learning disability from his or her parents.
Other factors may increase a child's chances of developing a learning disability. An imbalance of certain chemicals in the body can delay or permanently damage the development of the nervous system.
Even a child with no physical problem may develop a learning disability. Disabilities can result from a lack of the early learning experiences that stimulate mental growth and development. These experiences include hearing language, manipulating objects and exploring the environment.
There are many types of learning disabilities. Perceptual disorders, for example, hinder the brain's ability to organize and interpret sight and sounds. Perceptual disorders make learning to speak and read extremely difficult.
Another type affects memory. Children with this problem cannot easily recall what familiar objects look like or what sounds the objects make.
Other learning disabilities interfere with the ability to behave properly and concentrate.
Distractible children daydream almost constantly. They cannot direct their attention to any topic for more than a few minutes.
In contrast, children with a disability called perseveration cannot easily shift their attention from one activity to another. They may continue with a task long after it has been finished.
Hyperactive, or hyperkinetic, children cannot sit still. They speak and act on impulse and tend to become impatient and boisterous in the classroom.
Learning disabilities that block the development of language skills are called psycholinguistic disabilities. One such condition, called dysphasia, interfers with the ability to produce or understand human speech.
Dyslexia damages a child's capacity to understand printed or written words.
Dysgraphia affects the brain's control of the small finger muscles used in writing.
Learning problems that hinder a child's progress in particular school subjects, such as arithmetic or spelling, are called specific learning disabilities.