Dyslexia and the brain

Dyslexia is well-known to the general public, but unlike what most people think, it is not just about poor spelling!

From a neuropsychological perspective, dyslexia can be understood as a neurodevelopmental difficulty in how children (and adults) process information. It is characterised by the following cognitive difficulties:

1. Phonological awareness

Dyslexics have difficulty processing certain speech sounds and mapping sounds onto letters, a process call phonological awareness. This is considered the main reason for poor spelling skills.

2. Decoding skills

This refers to recognising the letters and sound that construct words. In dyslexia this is particularly difficult resulting in poor reading skills. It also results in a reduced vocabulary as the effort in decoding a word detract from learning its meaning. Not knowing what words mean impacts on understanding what you read. Thus poor decoding skills results in a poor vocabulary and in turn poor reading comprehension.

3. Poor working memory / short-term memory

Working memory is a specific brain process which holds information in mind to be used and manipulated without storing it as long term memory. Word decoding requires working memory. Over time, from repeated decoding a word is recognised and then stored as long term memory. This does not occur in dyslexia with words not recognised and thus not learnt (memorised). Interestingly memory for events, names of objects and friends may be perfectly intact!

4. Organising information

People with dyslexia may find it hard to sequence and organise information on a sound, word and paragraph level. This may be due to the effort in letter-sound decoding, but may also be due to an additional difficulty in organisation more generally, often making it hard for dyslexics to express themselves eloquently, despite high intelligence and creativity.

5. Poor writing skills

Poor handwriting is perhaps because letter-sound mapping is so effortful it uses up the available brain resources! However, it may also be due to associated difficulties with planning motor output (dyspraxia), fine motor skills and pencil grip (dysgraphia) or poor proprioception (visual-spatial disorientation). Often these difficulties can go together making the mechanics of writing very hard indeed.

Dyslexia is thus a term that describes a range of cognitive difficulties. This is because reading and writing uses multiple brain mechanisms that need to work together.

Dyslexia and the brain

Reading network in the brain

from:www.dyslexia-international.org

This image shows the brain networks involved in learning to read. It involves the occipital (visual), temporal (hearing and memory), parietal (visual-spatial) and frontal lobes (meaning, organisation and sequencing). The arrows show the connections between these regions. All the regions need to work together to translate what is seen into meaning. Amazingly the brain is wired for these processes to become automatic! It is as if we have been primed genetically for language to become like walking and eating. We do it without thinking.

Unfortunately for people with dyslexia these processes do not become automatic. Reading and writing remains remain effortful and over time results in great negativity about literacy.
It is now thought that the main difficulty in dyslexia is a problem with automaticity.

Cerebellum

Coordinated, fluid, automatic actions are orchestrated from the cerebellum in the back of the brain. From here, multiple connections are formed to other brain areas to refine processes that integrate motor and cognitive components. This may explain why children with dyslexia often have associated problems with posture and balance, coordination and muscle tone.

This difficulty in refining the integration of skills required for reading and writing may be due to genetic factors. For example, in children at risk for dyslexia, there is under-activation of specific language areas already present during infancy, even before a child understands language! Lower activation means poorer connections between this region and other brain areas over time.

This is why early intervention is important in children vulnerable to dyslexia as remediation programs can in fact enhance brain pathways between brain regions through practise which would not automatically occur.

An American study in 1998 showed that 95% of poor readers, who attended a school-based intervention aged 4-7, improved to being on par with their peers by age 9. However, those children attending the same intervention after age 9 still had problems with literacy at university level.

Why is assessment important?

The problem may not only be phonics!

Apart from atypical processing in language centres, problems with the integration of sensory information may impact language learning in children with intact language processing! For example, unidentified high-tone hearing loss and glue ear can impact auditory discrimination and cataracts, squinting or double vision can impact visual discrimination.

Problems on a language level may be due to other cognitive processes such as working memory, speed of information processing, visuospatial or poor organisation. These functions also develop at different rates, and what may appear as dyslexia in some children may just be slow maturation of abilities in relation to others. In such cases, idiosyncratic spelling for example, may be due to a child not able to remember and apply spelling rules, a problem with working memory, not language processing.

A full neuropsychological assessment is therefore critical as it examines all related brain systems, not just the ones used for reading and writing. This can identify which systems are slow at developing, not working, not interacting and where the breakdown occurs. This information allows us to tailor intervention specifically to those areas that need help and support. To do this effectively neuropsychologists require knowledge of brain and cognitive development i.e. how maturation of different brain systems allows certain mental processes to take place.

Early Intervention

Why does early intervention have better outcomes? Research suggests that there may be a critical period during age 5-7 when multiple brain connections may form between maturing brain systems at the back of the brain (cerebellum) and the more frontal, cortical areas. This process continues until adolescence, but certain sensory processes such as sound discrimination and letter-sound mapping are acquired quicker during the preschool years.

For older children, intervention may need to be tackled on the word level. Learning sight words may be more effective to improve fluency in reading. Fluency is super important for reading comprehension because getting stuck on decoding a word makes it almost impossible to follow a story. Thus focusing on learning words by sight, not decoding can improve understanding of what is read, despite spelling and writing remaining poor.

The overall aim of intervention should always be to maintain interest in literacy!

Early intervention is important to ensure that children suspected of dyslexia do not become negative about literacy, but for older children helping them to remain engaged in text, being able to access meaning and think about a passage (termed critical literacy) is more important that the mechanics of writing. Today technology can overcome writing difficulties – the use of word-processors, spell-checkers, speech translation software are examples of some solutions that can overcome poor spelling.

In future posts I will discuss the different approaches to intervention in more depth.

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