Neuroanatomical Research

Medical researchers have found differences in the brain structure of dyslexics. Albert Galaburda, M.D., Chief of the Division of Behavioral Neurology at Beth Israel Hospital in Boston and the Emily Fisher Landau professor of Neurology andNeurosciencee at Harvard University Medical School, is widely known for his research on the neural mechanisms of dyslexia. His theory of brain function depicts the brain as having processing stations connected by complex pathways. If there is a failure on one neural pathway, it may adversely affect processingelsewheree. Based on extensive research, he believes that the fundamental problem in dyslexia is a result of the brain’s propensity to develop small malformations (anomalies) in the cerebral cortex. According to Dr. Galaburda, in a normal brain, the thalamus, which contains relay centers for sensory and motor information to and from the brain, signals neurons to go to the language centers, In a dyslexic brain, something goes wrong and these neurons form excessive connections, causing nodules, or ectopias, to form on the cerebral cortex (surface of the brain). These nodules, which look like small bumps, represent a collection of brain cells which have migrated to the cerebral cortex in areas other than the known language centers. Their propagation causes systemic changes in the brain. In fact, the dyslexic brain is so different from the mature brain that it is hard to determine just where its language centers are located. As Dr. Galaburda noted, the fact that the low level visual processing and auditory processing brain cells located in the thalamus are 30 percent smaller than those of the ondyslexic brain is substantial and significant. Although small neurons cannot function as fast as large neurons, this in no way suggests that dyslexia is associated with low intelligence. In fact, most dyslexics are average or above average in intelligence. They just need more time to process information. Dr. Galaburda offered two theories regarding brain functions in dyslexia. The first theory places the onus of abnormality in the low-level processing areas of the brain. Because the neurons in this area are smaller than normal, the brain hears sounds in distortion and sees letters incorrectly. Consequently, when these garbled messages are sent to the higher level processing areas to be analyzed and used, they are further confused. This is referred to as a bottom-up problem. The second theory places the problem with the higher level processing areas of the brain. Since these are malformed, even if the auditory and visual messages are being correctly perceived, it is as if the top part of the brain says to the low level processing part of the brain, “Don’t bother to give me the message. I can’t use it anyway.” This theory would account for the presence of underdevelopedneuronss in the low-level structure of the brain. They are not being stimulated to send messages, so they have no reason to grow to a mature size. This is referred to as a top-down problem. Whichever is the case, the dyslexic can’t process the information in the same way that a nondyslexic brain can. Dr. Galaburda suspects that the problem is genetic and he is working with colleagues to map the gene. Through the use of the modern tools of anatomy, such as PET, EEG, SPECT, CAT, fMRI, rCBF, and BEAM, researchers are able to examine how the brain functions as it relates to language processing.February of 1998 made a breakthrough in understanding the functioning of the brain as it related to reading. Sally Shaywitz, M.D., and Bennett Shaywitz, M.D., co-directors of the Yale Center for Learning and Attention at Yale University Medical School, identified the “glitch in the circuitry” of the dyslexic brain’s pathway that is used for reading. Through the use of functional magnetic resonance imaging(fMRI), Drs. Shaywitz and Shaywitz were able to observe the brains of both dyslexics and non-dyslexics as they performed reading tasks. The fMRI enables researchers to distinguish between blood carrying oxygen and blood that is depleted of oxygen. An active area of the brain uses fresh supplies of oxygen-rich blood and appears to light up on the fMRI. In normal readers, the reading pathway encompasses fingertip-sized regions on the surface of the brain and moves from the back of the brain to the front. The path starts with the primary visual cortex, the area which registers what the eyes see. Then the visual association area, or angular gyrus, takes over, translating the abstract scrolls of words and letters into language. The final area, behind the eyes and toward the front of the brain, is the superior temporal gyrus, or Wernike’s area. Here the brain takes the sound of language and converts them into words. Comparative results of the study indicate that dyslexics barely use the normal reading pathway in the brain. Instead, they use the interior frontal gyrus, or Broca’s area, a region toward the front of the brain which pairs words with units of sound. According to Dr. Sally Shaywitz, “This provides evidence that dyslexia is a real biological entity.” Because of the brain’s plasticity, especially when Drs. Shaywitz and Shaywitz, aware of the prospect these implications reflect, plan to continue their research in hopes of learning how best to address this anomaly.