Dyslexia
Dyslexia & The Brain
The ability to be able to read text correctly is amongst the most important of academic skills that a child will learn, and in the modern and highly literate world of today, the academic, social, emotional and future financial consequences of having a Reading Disability are profound and far reaching.
When a child is assessed as having Dyslexia or a Specific Learning Difference, the link between the level of impairment in reading accuracy and comprehension in many cases does not correlate to the educational background and the measured level of intelligence of the child in question.
The perceptual and cognitive differences we notice in children who are later discovered to be dyslexic, occur in their short term memory – where they are not able to grasp and retain what they read, to changes in their occulomotor skills, sensory processing, visual and spatial abilities, processing sounds and being able to integrate the speech and letter sounds accurately.
These cognitive and perceptual changes are now being considered to be indicative of differences in brain activation patterns between children who are assessed to be dyslexic and their same age peers who are not impaired in their reading, writing and comprehension activities.
Scientists are now discovering that when children who are dyslexic or who manifest symptoms of the specific learning difference – are faced with a situation where they have to make progressive demands on their cognitive system for academic tasks that demand an age appropriate level of phonological understanding, the brain activation pattern that is noticed is very different from that of a normally developing child who can use his knowledge of having learnt the correct bottom up skills.
In the case of the dyslexic child, both the posterior and the anterior regions of the brain are now being indicated for anomalous activation patterns, which in turn are being said to be responsible for the cognitive and or behavioural deficits, which characterize dyslexic children. The posterior cortical systems include areas like the angular gyrus, extrastriate & striate cortex in addition to a certain specific area – the wernickes area where the dyslexic child is not able to increase activation as the task demand increases due to hypoactivation or under activation. In contrast these impaired readers show a pattern of over activation in the anterior regions like the left inferior frontal gyrus and BA 46/47/11.
These patterns of over and under activation are very different from normally developing children who have been blessed with the ability to read without any impairment and who are found to provide functional evidence of a widely distributed computational system for reading which is characterized by specialization and reciprocity.
We may wish it to be untrue, but the causes for dyslexia are neurological and to a large extent genetic in origin. Children inherit the genetic link for dyslexia and chances are that one of the child’s parents, grandparents, aunts or uncles would have been a dyslexic or is a dyslexic.
The functional disruption demonstrated in an extensive system in the posterior cortex encompassing both traditional visual and traditional language regions and a portion of the association cortex in a dyslexic child’s brain is of significance as the association cortex is considered pivotal in carrying out the cross modal integration necessary for fluid reading to happen.
Therefore when we hear the term that dyslexic children are normal children, but their brains are ‘wired differently’ we are not far from the mark and neither is it incorrect as what the child is manifesting is a result of a constitutionally based functional disruption where the system has just not developed normally.
(Studies of brains have advanced our understanding of dyslexia in important ways. Scientists have discovered structural differences in two parts of the dyslexic brain — the cerebral cortex and the thalamus. The cerebral cortex is the six-layered outer part of the brain involved in high-level processing, including sensory and motor analyses, working memory, attention, and language. The thalamus, a "way-station" located at the center of the brain, is the major stop for information transmitted from our sensory organs (e.g., eyes and ears) to the higher-level processing cerebral cortex. Microscopic examination of brains has revealed changes in the arrangement of nerve cells and a smaller auditory region — both in the cerebral cortex. Measurement of nerve cells in visual and auditory parts of the thalamus has revealed smaller cells. These studies provided the first evidence of a brain-based cause for developmental dyslexia.
Amongst the changes in the cortex one concerns ectopias, which are located within the first layer of the cortical areas responsible for language. Nerve cells normally are absent in this top layer. These ectopias are caused by a change during neuronal migration — the journey all newborn neurons undergo to their final positions in the brain. But some newborn cells miss their stops, travel too far, and end up in foreign locations in the cortex, becoming altered in the process and connecting to the rest of the brain in atypical ways. Scientists believe that ectopias occur in the developing brain of the fetus before its sixth month, since most neurons find their adult positions by that time. Because ectopias occur early in development and because dyslexia often runs in families, it is now suspect that genetic differences affecting early brain development cause ectopias.
Ectopic neurons seem to connect with neurons in other parts of the brain differently. Since most ectopias are in the language networks and the frontal part of the brain related to verbal memory, it can now be understood how a different "wiring" pattern might affect the complex process of learning to read and write.)
Besides learning shapes and sounds, children have to be able to correctly see the words they are trying to read. Research is emphasizing the presence of a deeper relationship between the visual circuitry of a child and the reading ability of the child. This circuitry is specific to the child’s ventral occipital – temporal cortex. In fact this area is relatively close to cortical regions critical for memory and language and the neural circuitry is well positioned to learn to recognize specific visual signals and communicate its analysis to cortical circuits specialized for sound and language.
Advances in understanding the visual cortex and the zones between the primary sensory and motor regions (association cortex) have led to specific views that these regions include retinotopic maps and have specific response patterns to visual stimuli and contain circuitry that can be modified by learning.
Therefore it is also - very important for a child to be able to ‘see’ the words in addition to understanding the shape to sound correlates.
If a child says that he cannot ‘see’ the words, either on the blackboard in the classroom at school or at home under a certain type of lighting system, parents may want to take his feedback seriously, rather than dismiss him as being naughty or uninterested in studies or wanting to avoid doing homework / class work.
Dyslexic children can be slightly disadvantage if the TO cluster neurons and their ensuing circuitry deficits lead to VS deficiencies.
The accumulating evidence from connectivity studies which is now gaining ground suggests that children with dyslexia and other reading disabilities may have deficits in the interaction amongst brain regions, or disrupted connectivity / ‘miswiring’ as it is more commonly known in day to day speak.
For parents seeking to alleviate the reading and academic difficulties for their son or daughter, hiring a ‘tutor’ to ‘teach’ a child academic text is of no value if the child cannot ‘see’ what he is reading and relate the structure of print to the phonemic basis of the character.
A lot of times, parents report that their son is ‘not good’ in studies, but that he is very good if the subject is visually explained to him. They claim that the child can ‘think’ in pictures. Unfortunately, what happens is that some children with dyslexia begin to use the right hemisphere as a compensatory mechanism for their reading disabilities. Dyslexic children, for whom the posterior areas of their brain are not working in harmony, compensate by using the homologues on the right side of the brain to try and understand text. While we may express caution at the role of the right-hemisphere homologous region during the early stages of literacy development, as this has not been investigated systematically, the compensatory mechanism used by certain children is a stark reality, which underscores the importance of early detection and intervention as the involvement of the right-hemisphere homologue in adults and children with dyslexia or at risk for reading problems, this recruitment is seriously being speculated to be a compensatory mechanism for the insufficient engagement of the left posterior dorsal system as explained above.
In fact, the right hemisphere homologue may play a similar role in young typically developing children and those with dyslexia. Concomitant changes in cortical activation with skill acquisition have been well documented and it is proposed that the regions that show greater activity during initial unskilled performance are recruited to cope with task demands (i.e., “scaffolding”). For instance, in the motor cortex where unimanual finger movements activate the region contralateral to the hand used, activity in the ipsilateral region has been reported during the performance of complex and untrained pattern of finger movements. In the language domain, a shift from a bilateral to left-lateralized pattern of recruitment during auditory word comprehension has been reported in infants from as early as 13 to 20 months in age. Bilateral or greater right hemisphere recruitment has also been reported in groups of adults with less expertise in a particular domain, including late learners and low proficiency native speakers during language processing.
Therefore, unskilled readers and children who develop dyslexia or emerging readers and those children whose initial problems with academic achievement are overlooked, the activation and dependency we are seeing in the right hemisphere homologues of the posterior dorsal region of the reading network may be a compensatory or scaffolding mechanism for them to be able to analyze and understand text in a clearer manner.
As we have mentioned above, compared to normal readers, adults and children with dyslexia show hypo activation in the posterior dorsal region in the left hemisphere. Therefore, the lack of engagement of the left posterior dorsal system seems to be emerging as a hallmark of reading disability, and the greater engagement of the right posterior dorsal region may be a consequence of the insufficient engagement of the left hemisphere system either due to immaturity or disability.
Dyslexia is a complex developmental disorder that must unfold in a complex chain of mental and brain developments, and much remains to be discovered about the etiology of dyslexia. The aim is to dissociate neural mechanisms related to the cause versus the consequence of dyslexia if we want to help children achieve academic success. An important issue that we at the Dyslexia Association of India™ believe in is that in the cognitive basis of dyslexia where neural systems are involved and are found not to be performing fluidly among poor readers during different processes like reading, writing, sentence comprehension, memory, recall etc - a high degree of consistency is being established. The parietotemporal area, particularly in the left hemisphere, appears to be a key locus of dysfunction in children who experience difficulty in learning to read. This conclusion is further supported by the finding that under-functioning in this area typifies struggling readers across a wide range of performance, manifesting in children with more severe reading impairment as well as those with less acute reading problems. Interestingly, this pattern is found despite the poor readers having an average or even high average level of IQ and across social and economic line.
Parents must own the responsibility for being the first responders to helping their children who are struggling and understand the importance of assessing reading problems within a neurodevelopmental context. A potentially significant aspect is that neural function during academic tasks is influenced by skill level as well as age, and the two factors contribute both independent and interacting effects. A critical implication of this is that the age at which poor readers are examined may influence the expression of impaired cortical function. (If a child is brought for assessment at a younger age and in an earlier grade in school the chances of helping this child are higher.) As the functioning of the cortical network involved in reading is dependent on a combination of interacting factors, including skill level, the maturity and integrity of the underlying neural systems, and the nature of the task various components of this network may be differentially called into play as children develop, gain increasing experience with text, and establish more efficient reading strategies.
Intervention and remediation of reading disabilities and dyslexia where changes are brought about in the child’s brain systems are a very specific and intensely demanding task that cannot be brought about by simplistic teaching and tuition. For morphometric changes to occur in a child’s brain the Dyslexia Association of India™ uses its patented T.R.A.I.N™ NeuroPlasticity programme in a very scientific manner to bring about cognitive improvement so that changes are visible, long term and based on neurological and morphological plasticity.
To learn more about the T.R.A.I.N™ programme, please click on the link. The DAI™ encourages parents to appreciate that children do ‘not’ – ‘not study’ on purpose. There has to be an underlying issue that is troubling the child and preventing effective acquisition of knowledge. Only when we accept that differences exist that we will be able to step forward to eliminate those differences.
The Dyslexia Association of India™ can be contacted on +91- 8826022886 or on e-mail at info@dyslexiaindia.org.in
