Study: Dyslexia not related to intelligence. Implications for discrepancy model?

NIH-fund­ed study finds dyslex­ia not tied to IQ (NIH press release):

At left, brain areas active in typ­i­cal­ly devel­op­ing read­ers engaged in a rhyming task. Shown at right is the brain area acti­vat­ed in poor read­ers involved in the same task.

- “Regard­less of high or low over­all scores on an IQ test, chil­dren with dyslex­ia show sim­i­lar pat­terns of brain activ­i­ty, accord­ing to researchers sup­port­ed by the Nation­al Insti­tutes of Health. The results call into ques­tion the dis­crep­an­cy mod­el — the prac­tice of clas­si­fy­ing a child as dyslex­ic on the basis of a lag between read­ing abil­i­ty and over­all IQ scores.”

- “In many school sys­tems, the dis­crep­an­cy mod­el is the cri­te­ri­on for deter­min­ing whether a child will be pro­vid­ed with spe­cial­ized read­ing instruc­tion. With the dis­crep­an­cy mod­el, chil­dren with dyslex­ia and low­er-than-aver­age IQ scores may not be clas­si­fied as learn­ing dis­abled and so may not be eli­gi­ble for spe­cial edu­ca­tion­al ser­vices to help them learn to read.”

Study Abstract

Although the role of IQ in devel­op­men­tal dyslex­ia remains ambigu­ous, the dom­i­nant clin­i­cal and research approach­es rely on a def­i­n­i­tion of dyslex­ia that requires read­ing skill to be sig­nif­i­cant­ly below the lev­el expect­ed giv­en an individual’s IQ. In the study report­ed here, we used func­tion­al MRI (fMRI) to exam­ine whether dif­fer­ences in brain acti­va­tion dur­ing phono­log­i­cal pro­cess­ing that are char­ac­ter­is­tic of dyslex­ia were sim­i­lar or dis­sim­i­lar in chil­dren with poor read­ing abil­i­ty who had high IQ scores (dis­crepant read­ers) and in chil­dren with poor read­ing abil­i­ty who had low IQ scores (nondis­crepant read­ers). In two inde­pen­dent sam­ples includ­ing a total of 131 chil­dren, using uni­vari­ate and mul­ti­vari­ate pat­tern analy­ses, we found that dis­crepant and nondis­crepant poor read­ers exhib­it­ed sim­i­lar pat­terns of reduced acti­va­tion in brain areas such as left pari­etotem­po­ral and occip­i­totem­po­ral regions. These results con­verge with behav­ioral evi­dence indi­cat­ing that, regard­less of IQ, poor read­ers have sim­i­lar kinds of read­ing dif­fi­cul­ties in rela­tion to phono­log­i­cal pro­cess­ing. Key­words: aca­d­e­m­ic achieve­ment, apti­tude mea­sures, dyslex­ia, neu­roimag­ing, reading.

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Relat­ed articles:

• Unlock­ing dyslex­ia in Japanese
• Major grant to study brain basis of autism and dyslexia