By Gordon Sherman, Ph.D.
The answers to these questions are, respectively: you can, you would, and no! Modern neuroimaging has made it possible to "see" inside living, performing human brains. Using high-tech imaging tools, scientists have discovered that dyslexic brains do function in atypical ways consistent with the structural differences discovered nearly two decades ago. Finally, these are findings from the pages of scientific journals, not from science-fiction literature.
Neuroimaging provides a computer-analyzed view of how the brain looks and functions, showing which areas "are activated" (i.e., working hard) and which are not. We can watch the brain while it performs complex cognitive activities and while it is at rest, though it never really rests. While technological advances promise ever-sharper images, today's neuroimaging techniques and computers already provide an arresting view of the brains of people with dyslexia. There are new findings on subtle structural differences, but the most intriguing findings concern functional attributes - how these brains work differently.
Studies from around the world show a distinctly different pattern of brain activity in subjects with dyslexia as compared to people without dyslexia.
Neuroimaging studies from the United States, Japan, Germany, Italy, and other countries compared impaired (dyslexic) readers to unimpaired (control) readers ranging in age from 8 to 54. A variety of imaging techniques (fMRI, PET, MEG, MSI) monitored subjects' brain activity. The most commonly used technique, fMRI, is safe and noninvasive and uses radio waves and magnetic fields to show blood flow in areas of the right and left hemispheres. Areas with increased blood flow are hard at work and show increased "activation."
In these studies, subjects performed phonological-processing tasks (e.g., silent reading, rhyming, or pronouncing words and nonsense words). Some consistent findings emerged. The first is that during these language-based tasks, key areas of the language network in the left temporal, parietal, and occipital lobe "under-activated" in people with dyslexia, while left frontal areas "over-activated." The second finding is that, in subjects with dyslexia, certain right-hemisphere areas "over-activated."
What do these findings mean? In most people, left-hemisphere areas specialize in language and "activate" on language tasks, reflecting a specialized brain design that, in general, promotes efficiency. However, these new studies showed the brains of subjects with dyslexia function more bilaterally - in other words, they use areas in both hemispheres for language tasks, usually a less efficient mode for processing sequential information and certain language skills.
The increased activity in both the left-hemisphere frontal area and in areas of the right hemisphere may reflect compensatory mechanisms working to bypass deficiencies in left-hemisphere language areas. Neural compensation is a good strategy for circumventing specific structural and functional shortcomings, a phenomenon well-known in cerebral-stroke patients who learn to accommodate to an injury by transferring function from damaged to intact regions of the brain. A similar but developmentally unique phenomenon appears to be at work in dyslexia, though the compensation mechanism may be imperfect and inefficient, not entirely correcting the hallmark phonological difficulties often found in people with dyslexia.
Bilateral hemisphere activity also may relate to the structural symmetry in dyslexic brains. Areas in the right and left hemisphere of people with dyslexia are more symmetrical, more like mirror images, whereas these areas in most people are asymmetrical.
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