Anomalous Cerebral Structure in Dyslexia Revealed With Magnetic Resonance Imaging

Abstract

\s=b\ Objective.\p=m-\Todevelop quantitative methods for identifying cerebral anomalies on magnetic resonance images of subjects with language disorders and other learning disabilities. Design.\p=m-\Partially blinded comparison of subjects with dyslexia, unaffected relatives, and a control group balanced for age and socioeconomic status. Criterion standard: clinical diagnosis of dyslexia by physician or learning disabilities specialist on the basis of clinical assessment and family history.Settings.\p=m-\Hospitalpediatric neurology clinic and private reading clinic.Patients and Other Participants.\p=m-\Volunteers: individuals with dyslexia (seven male and two female, aged 15 to 65 years) from professional families; unaffected first-and second\x=req-\ degree relatives (four male and six female, aged 6 to 63 years) available in the geographical area; and controls (five male and seven female, aged 14 to 52 years).Interventions.\p=m-\Gradient echo three-dimensional scan in Seimens 1-Tesla Magnetom; 128 1.25-mm consecutive sagittal images.Main Outcome Measures.\p=m-\(1) Average length of the tem-poral (T) and parietal (P) banks of the planum temporale;(2) interhemispheric coefficients of asymmetry for T and P banks: Left-Right interhemispheric coefficients of asymmetry= (L-R)/[(L+R)/2];(3) intrahemispheric coefficients of asym-metry=(T-P)/[(T+P)/2]; and (4) qualitative assessment of gyral variants in the parietotemporal operculum.Results.\p=m-\All groups had left-sided asymmetry for the temporal bank and right-sided asymmetry for the parietal bank.The group with dyslexia had exaggerated asymmetries, owing to a significant shift of right planar tissue from the temporal to parietal bank. They also had a higher incidence of cerebral anomalies bilaterally (subjects with dyslexia, six of nine; relatives, two of 10; and controls, zero of 12).Conclusions.\p=m-\Quantitative assessment of high-resolution magnetic resonance images can reveal functionally relevant variations and anomalies in cerebral structure. Further refinement of these measurement techniques should improve the diagnosis, classification, and treatment of language disorders and other learning disabilities.Early investigators believed that neuroanatomical cor-

Enhancement of brain event-related potentials to speech sounds is associated with compensated reading skills in dyslexic children with familial risk for dyslexia

“…The brain symmetry in dyslexics suggest anatomical differences in areas activated heavily by speech and language and possibly differences in the distribution of activity in the left and right perisylvian cortex (Binder et al, 1996;. However, also different hemispheric symmetry patterns of posterior perisylvian areas, including planum temporale, have been observed in dyslexic individuals (Chiarello et al, 2006;Leonard et al, 1993).…”

“…Regardless of the commonly reported reduced asymmetry, also asymmetry has been reported: adults with familial risk and earlier history of clinically diagnosed dyslexia, but whose reading skills were later compensated, showed leftward asymmetry of planum temporale (Chiarello et al, 2006;Leonard et al, 1993). Leonard et al (1993) studied compensated adult dyslexics as well as their first or second-degree unaffected relatives. They found that the relatives had less cerebral anomalies and better scores in phonological awareness as compared to compensated dyslexics, yet more anomalies and lower scores than in the control group.…”

“…Reduced leftward asymmetry of the planum temporale in the posterior Sylvian fissure has been observed, compared to controls . However, an extreme leftward asymmetry of the planum temporale has also been reported in compensated dyslexic adults with familial risk, which has been suggested to be a consequence of enhanced top-down processing (Chiarello et al, 2006;Leonard et al, 1993). It has been stated that probably deviation in both directions from average on a symmetry-asymmetry scale can lead to deficient reading skills: small symmetrical brain structures would be associated with deficits in multiple domains of language and larger asymmetrical structures with more isolated phonological deficits that are compensated for until adulthood .…”

“…For example, dyslexics have been suggested to have more symmetrical hemispheres in general, as well as symmetrical specific brain structures such as plana temporale in the posterior Sylvian fissure, which might affect the brain activation originating from these areas involved in speech and language processing (Binder et al, 1996;. Regardless of the commonly reported reduced asymmetry, also asymmetry has been reported: adults with familial risk and earlier history of clinically diagnosed dyslexia, but whose reading skills were later compensated, showed leftward asymmetry of planum temporale (Chiarello et al, 2006;Leonard et al, 1993). Leonard et al (1993) studied compensated adult dyslexics as well as their first or second-degree unaffected relatives.…”

Development of structure and function in the infant brain: Implications for cognition, language and social behaviour

“…This seemingly basic ability has been demonstrated to be important for language functioning. A large literature implicates basic difficulties in processing brief or rapidly occurring successive auditory cues, for both speech and non-speech stimuli, in the poor phonological skills which are observed in language-based learning disorders (LLI; for reviews see Leonard, 1998;Tallal, 2004;Tallal et al, 1998;Wright et al, 2000).…”