Dys­lexia – it’s faulty wiring, says new study

The Star Malaysia - Star2 - - SCIENCE -

A ROAD­BLOCK in the brain makes read­ing dif­fi­cult for peo­ple with dys­lexia, a new study sug­gests, con­tra­dict­ing long-held opin­ion.

The find­ings in the US jour­nal Sci­ence add to an on­go­ing de­bate over whether the in­her­ited neu­ro­log­i­cal dis­or­der is caused by faulty brain wiring or the brain’s in­abil­ity to un­der­stand the in­ter­ac­tion of sounds and sym­bols that form lan­guage.

Dys­lexia is a learn­ing dis­abil­ity that af­fects about 10% of the US pop­u­la­tion and oc­curs among peo­ple of all eco­nomic and eth­nic back­grounds.

The find­ings were based on brain scans of 23 peo­ple with dys­lexia and 22 with­out, show­ing dyslex­ics un­der­stand the sound units fine, but lack the brain con­nec­tions to process them.

“Quite to our sur­prise, and prob­a­bly to the sur­prise of the broader dys­lexia field, we found that pho­netic rep­re­sen­ta­tions are per­fectly in­tact in adults with dys­lexia,” said re­searcher Bart Boets, a pro­fes­sor of psy­chi­a­try at the Univer­sity of Leu­ven in Bel­gium.

Boets said the re­search coun­ters the opin­ion that peo­ple with dys­lexia have an in­fe­rior abil­ity to recog­nise the dis­tinct sounds of lan­guage.

In­stead, they found im­paired con­nec­tions be­tween the right and left au­di­tory re­gions, where pho­netic rep­re­sen­ta­tions are pro­cessed, and Broca’s re­gion, where higher level phono­log­i­cal pro­cess­ing takes place.

Study sub­jects lis­tened to a se­quence of four par­tial words, fol­lowed by another se­quence in which a con­so­nant or vowel had been switched, such as ba-baba-ba, da-da-da-da, and asked to iden­tify what changed.

The team used ad­vanced func­tional mag­netic res­o­nance imaging (fMRI) tech­niques to mea­sure the unique fin­ger­print of each sound in the brain, and found the qual­ity of im­pres­sions was the same in nor­mal read­ers and dyslexic peo­ple.

In other words, their brains were iden­ti­fy­ing the sounds and their changes just like nor­mal read­ers.

How­ever, the dyslexic peo­ple took 50% longer to make their re­sponses, ac­cord­ing to Sci­ence.

Re­searcher Hans Op de Beeck likened the ex­per­i­ment to hav­ing his daugh­ter call from the land­line tele­phone at their house to say she was home from school. That, he could ver­ify, but what was she do­ing at home? Was she do­ing her home­work or play­ing a game? He could not know for sure. With this ex­per­i­ment, re­searchers were able to see that “the re­gions con­tain­ing pho­netic rep­re­sen­ta­tions in adult dyslexic read­ers are do­ing their home­work, that’s for sure.”

Boets said he hopes the re­search could lead to bet­ter ways of im­prov­ing the brain cir­cuitry, per­haps through non­in­va­sive brain stimulation tech­niques.

The find­ings were ques­tioned by neu­ro­sci­en­tist Michael Merzenich at the Univer­sity of Cal­i­for­nia, San Fran­cisco.

Decades of “very ex­ten­sive and com­pelling” ev­i­dence show that peo­ple with dys­lexia process pho­netic rep­re­sen­ta­tions with lower fidelity than nor­mal, he said. – AFP

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