What Causes Learning Disabilities
Understandably, one of the first questions parents ask when they learn their child has a learning disorder is “Why? What went wrong?”
Mental health professionals stress that since no one knows what causes learning disabilities, it doesn’t help parents to look backward to search for possible reasons. There are too many possibilities to pin down the cause of the disability with certainty. It is far more important for the family to move forward in finding ways to get the fight help.
Scientists, however, do need to study causes in an effort to identify ways to prevent learning disabilities.
Once, scientists thought that all learning disabilities were caused by a single neurological problem. But research supported by NIMH has helped us see that the causes are more diverse and complex. New evidence seems to show that most learning disabilities do not stem from a single, specific area of the brain, but from difficulties in bringing together information from various brain regions.
Today, a leading theory is that learning disabilities stem from subtle disturbances in brain structures and functions. Some scientists believe that, in many cases, the disturbance begins before birth.
Errors in Fetal Brain Development
Throughout pregnancy, the fetal brain develops from a few all-purpose cells into a complex organ made of billions of specialized, interconnected nerve cells called neurons. During this amazing evolution, things can go wrong that may alter how the neurons form or interconnect.
In the early stages of pregnancy, the brain stem forms. It controls basic life functions such as breathing and digestion. Later, a deep ridge divides the cerebrum – the thinking part of the brain – into two halves, a right and left hemisphere. Finally, the areas involved with processing sight, sound, and other senses develop, as well as the areas associated with attention, thinking, and emotion.
As new cells form, they move into place to create various brain structures. Nerve cells rapidly grow to form networks with other parts of the brain. These networks are what allow information to be shared among various regions of the brain.
Throughout pregnancy, this brain development is vulnerable to disruptions. If the disruption occurs early, the fetus may die, or the infant may be born with widespread disabilities and possibly mental retardation. If the disruption occurs later, when the cells are becoming specialized and moving into place, it may leave errors in the cell makeup, location, or connections. Some scientists believe that these errors may later show up as learning disorders.
Other Factors That Affect Brain Development
Through experiments with animals, scientists at NIMH and other research facilities are tracking clues to determine what disrupts brain development. By studying the normal processes of brain development, scientists can better understand what can go wrong. Some of these studies are examining how genes, substance abuse, pregnancy problems, and toxins may affect the developing brain.
Genetic Factors – The fact that learning disabilities tend to run in families indicates that there may be a genetic link. For example, children who lack some of the skills needed for reading, such as hearing the separate sounds of words, are likely to have a parent with a related problem. However, a parent’s learning disability may take a slightly different form in the child. A parent who has a writing disorder may have a child with an expressive language disorder. For this reason, it seems unlikely that specific learning disorders are inherited directly. Possibly, what is inherited is a subtle brain dysfunction that can in turn lead to a learning disability.
There may be an alternative explanation for why LD might seem to run in families. Some learning difficulties may actually stem from the family environment. For example, parents who have expressive language disorders might talk less to their children, or the language they use may be distorted. In such cases, the child lacks a good model for acquiring language and therefore, may seem to be learning disabled.
Tobacco, Alcohol, and Other Drug Use – Many drugs taken by the mother pass directly to the fetus. Research shows that a mother’s use of cigarettes, alcohol, or other drugs during pregnancy may have damaging effects on the unborn child. Therefore, to prevent potential harm to developing babies, the U.S. Public Health Service supports efforts to make people aware of the possible dangers of smoking, drinking, and using drugs.
Scientists have found that mothers who smoke during pregnancy may be more likely to bear smaller babies. This is a concern because small newborns, usually those weighing less than 5 pounds, tend to be at risk for a variety of problems, including learning disorders.
Alcohol also may be dangerous to the fetus’ developing brain. It appears that alcohol may distort the developing neurons. Heavy alcohol use during pregnancy has been linked to fetal alcohol syndrome, a condition that can lead to low birth weigh, intellectual impairment, hyperactivity, and certain physical defects. Any alcohol use during pregnancy, however, may influence the child’s development and lead to problems with learning, attention, memory, or problem solving. Because scientists have not yet identified “safe” levels, alcohol should be used cautiously by women who are pregnant or who may soon become pregnant.
Drugs such as cocaine – especially in its smokable form known as crack – seem to affect the normal development of brain receptors. These brain cell parts help to transmit incoming signals from our skin, eyes, and ears, and help regulate our physical response to the environment. Because children with certain learning disabilities have difficulty understanding speech sounds or letters, some researchers believe that learning disabilities, as well as ADHD, may be related to faulty receptors. Current research points to drug abuse as a possible cause of receptor damage.
Problems During Pregnancy or Delivery – Other possible causes of learning disabilities involve complications during pregnancy. In some cases, the mother’s immune system reacts to the ferns and attacks it as if it were an infection. This type of disruption seems to cause newly formed brain cells to settle in the wrong part of the brain. Or during delivery, the umbilical cord may become twisted and temporarily cut off oxygen to the fetus. This, too, can impair brain functions and lead to LD.
Toxins in the Child’s Environment – New brain cells and neural networks continue to be produced for a year or so after the child is born. These cells are vulnerable to certain disruptions, also.
Researchers are looking into environmental toxins that may lead to learning disabilities, possibly by disrupting childhood brain development or brain processes. Cadmium and lead, both prevalent in the environment, are becoming a leading focus of neurological research. Cadmium, used in making some steel products, can get into the soil, then into the foods we eat. Lead was once common in paint and gasoline, and is still present in some water pipes. A study of animals sponsored by the National Institutes of Health showed a connection between exposure to lead and learning difficulties. In the study, rats exposed to lead experienced changes in their brainwaves, slowing their ability to learn. The learning problems lasted for weeks, long after the rats were no longer exposed to lead.
In addition, there is growing evidence that learning problems may develop in children with cancer who had been treated with chemotherapy or radiation at an early age. This seems particularly true of children with brain tumors who received radiation to the skull.
Are Learning Disabilities Related to Differences in the Brain?
In comparing people with and without learning disabilities, scientists have observed certain differences in the structure and functioning of the brain. For example, new research indicates that there may be variations in the brain structure called the planum temporale, a language-related area found in both sides of the brain. In people with dyslexia, the two structures were found to be equal in size. In people who are not dyslexic, however, the left planum temporale was noticeably larger. Some scientists believe reading problems may be related to such differences.
With more research, scientists hope to learn precisely how differences in the structures and processes of the brain contribute to learning disabilities, and how these differences might be treated or prevented.