Cause of dyslexia: Dysfunctioning Brain Connection

Until now, the cause of dyslexia was not known, although there were indications that certain areas of the brain responsible for processing sounds did not work properly. Researchers have discovered that these areas work well in people with dyslexia, but that there are certain brain connections that function less well in dyslexics. The results of this research were published in Science at the end of 2013.


The word dyslexia is also called word blindness. The word comes from Greek and is made up of two parts; dys, which means malfunctioning, and lexis which means language or words. People with dyslexia have difficulty reading, spelling and writing words, despite otherwise having a normal intelligence level. More than ten percent of the world’s population has some form of dyslexia.

The diagnosis of dyslexia

In the Netherlands, the diagnosis of dyslexia is made by a doctor, healthcare psychologist or educational psychologist who is included in the BIG register. To make the diagnosis, it must be determined that the reading, spelling and writing problems have no other cause.
It is important that the diagnosis of dyslexia is discovered at the earliest possible age. Children with dyslexia can then receive extra guidance in learning (technical) reading and receive extra exercises. Research has shown that the sooner writing and reading problems are addressed, the greater the final result.


Dyslexia is more common in men than in women and a hereditary factor most likely plays a role. If one of the parents has been diagnosed with dyslexia, the chance that the child has some degree of dyslexia is 40 to 50%. When both parents are dyslexic, this chance is even 80%.


One hypothesis for the existence of dyslexia is that the sounds of words are distorted or less well represented in the brains of people with dyslexia. Phonics are used in reading, and therefore not processing phonics properly can lead to problems with reading, spelling and writing. Words such as ‘ball’ and ‘valley’ can be difficult to tell apart. To investigate what the real problem is in the brains of dyslexics, researchers made functional MRI scans (fMRI scans) of the brains of 23 people with diagnosed dyslexia and 22 people without dyslexia. While making the scan, the subjects had to listen to spoken words and perform a task in which they had to distinguish between different sounds. Using the scan, the researchers looked at which brain areas became active while performing the tasks.

Dysfunctional connection

The fMRI showed that the brain areas involved in processing sounds in dyslexics worked just as well as in people without dyslexia. In some cases, the sounds in the dyslexics’ brains were even reproduced better. The researchers have thus rejected the hypothesis of distorted sound representation. What the researchers did find was that the connection between the part of the brain that processes sounds (the auditory cortex) and the part that converts the sounds into language (Broca’s area) did not function properly in people with dyslexia. The sounds are therefore reproduced well, but the area of the brain that is responsible for converting the sounds into language cannot be reached because the communication between the two areas is disrupted.


The researchers hope that the new insights can lead to improvements in training for people with dyslexia. These should be specifically aimed at improving the connections between the brain areas responsible for representing sounds and converting them into language.

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  • Functional MRI (fMRI): Demonstration of brain activity