Causes of Learning Disabilities
In most cases, the cause (etiology) of a child’s learning disability is unknown. Many causes have been proposed, a situation that probably reflects the highly diverse nature of students with learning disabilities. Just as there are different types of learning disabilities (e.g., dyslexia, language disabilities, math disabilities), there are likely to be different causes. Four suspected causal factors are brain damage, heredity, biochemical imbalance, and environmental causes.
Brain Damage or Dysfunction
Some professionals believe that all children with learning disabilities suffer from some type of brain injury or dysfunction of the central nervous system. Indeed, this belief is inherent in the NJCLD definition of learning disabilities, which states that learning disorders are “presumed to be due to central nervous system dysfunction.” In cases in which actual evidence of brain damage cannot be shown (and this is the situation with the majority of children with learning disabilities), the term minimal brain dysfunction is sometimes used, especially by physicians. This wording implies brain damage by asserting that the child’s brain does not function properly.
Recent advances in magnetic resonance imaging (MRI) technology have enabled researchers to discover that specific regions of the brains of some individuals with reading and language disabilities show activation patterns during phonological processing tasks that are different from the patterns found in the brains of nondisabled individuals (Miller, Sanchez, & Hynd, 2003; Richards, 2001; Simos, Breier, Fletcher, Bergman, & Papanicolaou, 2000). The actual structure of the brain of some children with reading disabilities is slightly different from that of children without disabilities (Leonard, 2001).
This research holds great promise for understanding the biological bases of dyslexia and other specific learning disabilities. However, as Leonard (2001) points out, we do not yet know how and to what extent the brain’s neural networks are affected by the child’s experiences (i.e., learning) and vice versa. Thus, we do not know whether neurobiological factors associated with learning disabilities contribute to the learning problems of children, are the product of an unstimulating environment, or a combination. However, there is growing evidence that differences in the ways in which reading-disabled and normal children’s brains are activated weakens with intensive remedial reading instruction (Richards, 2001). Shaywitz et al. (2004) reported that an average of 105 hours of individual tutoring that focused on teaching the alphabetic principle (how letters and combinations of letters represent the small segments of speech called phonemes) and oral reading fluency practice not only improved children’s reading fluency but “facilitated the development of the neural systems that underline skilled reading”.
Special educators must be aware of placing too much emphasis on theories linking learning disabilities to brain damage or brain dysfunction, for three major reasons. First, not all children with learning disabilities display clinical (medical) evidence of brain damage, and not all children with brain damage have learning disabilities. The second problem is that assuming a child’s learning problems are caused by a dysfunctioning brain can serve as a built-in excuse for ineffective instruction. When a student with suspected brain damage fails to learn, his teachers may be quick to presume that the brain injury prevents him from learning and be slow to analyze and change instructional variables. Third, whether “learning disabilities in an individual case are symptoms that result from brain injury or developmental delay will not essentially alter the methods of teaching the student” (Myers & Hammill, 1990, p. 22).
Current interpretations of the role of constitutional factors show reciprocal relations with the environment, such that environmental factors (e.g., instruction) must be in place to develop the neural networks that support academic skills. Even genetic studies of reading disability show that only about 50 percent of the variability in reading skills can be explained by genetic factors—the remainder is environmental. Learning disabilities represent interplays of constitutional and environmental factors that are not yet well understood. (Fletcher et al., 2001, p. 7)
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