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As far as symmetry of the hemispheres, the majority of the neurological research for SLDs, especially RDs, has been these studies of hemisphere symmetry through the morphology of the corpus callosum and the planum temporale region. Galaburda et al.found differences in language function areas for people with SLDs, such as symmetry or reversed asymmetry of Wernicke's area and chaotic patterns of the planum temporale region. This data may correlate with Gross-Glen et al. and Duara in finding metabolic activity differences in the prefrontal and inferior visual/lingual areas of the brain for RD and the temporal area for normal readers.
The corpus callosum has been studied for symmetry morphology and transmission activity with SLDs having more symmetrical (Rosen et al.)or reverse asymmetry (Heir et al., 1978). Reverse asymmetry is opposite the norm of the left hemisphere being larger than the right. Heir et al. found reverse asymmetry in SLD with a wider posterior right hemisphere. In addition to this reverse asymmetry, Filipek et al. also found the right hemisphere to be wider in the posterior and narrower overall with the left hemisphere being the same as the norm. Gross-Glen et al. and Duara et al. had the most information on the corpus callosum being more shallow in SLD with little separation. Yet, the right hemisphere was larger than the left in the midposterior angular gyrus region of the inferior parietal lobe. Also, people with RDs had a large splenum and a more narrow callosum allowed for more interhemispherical activity. The meaning through function of these areas will be analyzed in further depth for the conclusion.
The other major symmetry morphology study was the planum temporale region which was different without the normal asymmetry of a larger left side (Galaburda et al., Hynd, Geschwind). Hynd also found that language areas were shorter for SLDs and had reverse asymmetry (left side longer than the right) in posterior temporal with the planum temporale. Galaburda was most notable for finding heterotopias, abnormal locations of cerebral cortex collections) like the planum temporale as a surface area in the visual cortex which is the superior surface of the temporale lobe.
Overall, these studies have shown perceptual deficits: in vision related to impaired motion detection and in phonology related to impaired coding. This impairment is related to symmetry, reversed asymmetry, and lower numbers of neurons in, predominantly, the temporal lobes and visual motion areas of the occipital lobe. Also, the auditory deficits may be closely related to temporal abnormalities that impede speed and accuracy for speech-sound relationships in reading of the planum temporale region, as well as the thalamus near the corpus callosum.
For memory of letter sequence problems in dysgraphia, Cipolotti and Warrington (1996) noticed a stroke victim of left hemisphere wrote each letter as read to him for word recognition and comprehension. Similarly, SLDs are cross-cultural as damage to corpus callosum has effected Japanese patients abilities to write Kana (vowel-like) and Kanji (consonant-like) (Carlson 1998 p504).

The Contradictory Corpus Collosum
Although sporadic, a steady stream of research has focused on the noted differences in the size and shape of the dyslexic corpus callosum (CC). The CC is a central nerve bundle that allows communication between the right and left lobes of the brain. Because it is so integrally involved in interhemispheric communication, researchers believe that any significant malformities of the CC could lead to serious disruptions in the processing of sensory information.
The evidence implicating the CC, however, is often conflicting and confusing. One study, for example, reports that children with dyslexia have abnormalities in the corpus callosum. The results, however, show no particular trend -- many of the dyslexic children had either an undersized or oversized corpus callosum (Njiokiktjien et al.,1994). Other studies which have found that the anterior region of the genu of the corpus callosum in dyslexics is significantly smaller than normal (Hynd et al., 1995), are only followed by studies which show that the posterior region is significantly larger and the only CC region affected (Rumsey et al., 1996).
In addition to possible size differences, other experimental evidence suggests that dyslexics have a thicker corpus collosum. This research suggests that increased thickness prevents neurons from making the appropriate connections across the CC, inhibiting right hemispheric competence and impairing reading abilities (Njiokiktjen et al., 1993). Analyzing this information, it becomes clear that researchers studying the corpus callosum have been left in a precarious position. While at once they face evidence too interesting to ignore, they are also left only with results still too rudimentary to draw conclusions.