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The Brain and Dyslexia

Professor Dr Dirk Bakker, Ph.D,
Professor-Emeritus, Free University, Amsterdam;
Director, European Graduate School of Child Neuropsychology

This is a shortened version of the original text by Dirk J. Bakker: ‘Dokteren aan dyslexie’ – from E. van Aarle & K. Henneman (Eds.), Dyslexie ’92 (pp.159-170); Amsterdam/Lisse, Netherlands: Swets & Zeitlinger, 1993. All references are listed in the original version. Translation by Peter Arthern, OBE.

Introduction
In talking about dyslexia we are also talking about the process of reading. Reading is cognitive behaviour and is therefore carried out by the brain. So when we talk about reading, then we must also be talking about something to do with the brain.

But what is this something? Recently a substantial amount of attention has been given to what the brains of dyslexic people look like and how they function.

What follows is a survey of the scientific approach to dyslexia based on my own knowledge to date. This is a huge task in a limited space and I have tailored this article to convey the kind of information that readers of this Guide might find useful.

If we use the brain as our starting point, we are faced with such questions as:

1. What is special about dyslexics’ brains?
2. What is the origin of this special feature?
3. How does this special feature manifest itself?
4. What intervention is appropriate?

The Brain
The brain is made up of billions of nerve cells, or neurons, which communicate with each other along an electro-chemical path. Although the brain operates as a single entity, there are substructures and subsystems. It is divided into left and right hemispheres which are connected by the ‘corpus callosum.’ In most people the left side is responsible for the reception and production of language, while the right hemisphere plays an important part in visio-spatial (vision and the assessment of spatial) information. Each hemisphere has a cortex or bark with a white substance below it. The cortex contains mainly the body of the nerve cells; the white substance contains the connections.

The cells in the cortex move from deeper areas of the cortex during development prior to birth. Not all the cells may reach their final destination; they may collect into clusters of cells along the way. These ‘misplaced’ groups of cells are called ectopias.

The cortex of each hemisphere is divided into four functional areas: the frontal, parietal, temporal and occipital lobes. All these areas are involved in the complex activity of reading, particularly the temporal and occipital areas and the transition area between the two, the parietal lobe.

Nerve cells communicate with each other electro-chemically. This electrical activity can be measured outside the brain by means of an electroencephalogram (EEG) and techniques derived from it.

Question 1: What is special about dyslexics’ brains?

In spite of extensive scientific research, here there are still more questions than answers. Recent research has thrown some light on the subject, but it is important to make a distinction between answers relating to the structure, or anatomy, of the brain and those relating to its physiology, or functioning.

Question 1.1: Anatomically special?

What is anatomically special about the dyslexic’s brain?

• Ectopic cells were found in all the dyslexics’ brains examined during the Harvard University anatomical research programme. They were found in many places, but especially in the left temporal and frontal lobes, that is in the areas important for language.
  
• Other researchers have shown that the ‘planum temporale’ tissue shows a symmetry in dyslexics’ brains which is not evident in the brains of the majority of non-dyslexics.
• In dyslexics’ brains, the cells of the magnocellular system appear smaller than normal. It looks as if two main systems are involved in visual perception, the magnocellular and the parvocellular system. The parvocellular system is adapted for the perception of form and colour and the magnocellular for the perception of movement. The magnocellular system plays a prominent role in the rapid changes of images which are peculiar to reading. If this system proves inadequate, difficulties with reading will result.

This summary of anatomical discoveries gives rise to two questions and comments:

Has it been shown that dyslexia is caused by subtle anatomical deviations in the brain?

A causal connection has not been shown. It is known that the dislocation of cells occurs in several neurological conditions and that such misplacement of cells is not specific to dyslexia. This, however, does not alter the fact that some researchers consistently showed that dyslexia bears some relation to subtle deviations of the brain in areas which are prominent in the process of learning language and reading.

What do the ectopic or misplaced cells have to do with a specially large right-sided planum temporale, and what does this have to do with an insufficient magnocellular system?

At present, these questions can not be answered adequately.

Question 1.2: Physiologically special?

Neurophysiology and neuropsychology make much use of the electroencephalogram (EEG) and techniques derived from it. In addition, Positron Emission Tomography (PET) scans are used: glucose or another chemical is introduced into the bloodstream while a particular task is being carried out; the chemical introduced, which is made radioactive very briefly, is taken up more intensively by those parts of the brain which are most closely connected with reading.

Frequently these scans are used to examine people manifesting symptoms of dyslexia. Modern technology makes it possible to show a full representation of the electrophysiological activity of the whole cortex while the subject is reading. This type of research into normal and deviant reading is currently under way in the Netherlands. Using electrophysiology on people with differing reading skills has shown that:

• the beginner demonstrates activity in the right hemisphere of his brain whilst reading
• the advanced reader activates his left hemisphere, and
• the dyslexic shows an unusual variation in the distribution of brain activity.

One theory suggests that there is a dynamic interactive neuronal model for the recognition of letters and words. The essential characteristics of a letter are picked up by nerve cells in the brain. For example, ‘line from bottom left to top right, line from bottom right to top left.’ On the basis of this information, signalled through other cells, the recognition of the letter ‘A’ takes place. The scanning of a letter’s characteristics and the identification of the letter itself are presented as electric potentials which have a certain frequency and amplitude and which are extinguished after a certain time. If the letters are presented rapidly, as in the case of reading, it could be that the processing of one letter is not finished before that of another is started. It can be determined mathematically that the potentials can reach chaotic proportions, can extinguish each other, and letters could be missed when reading. These problems happen frequently to people with dyslexia. One explanation for this electro-physiological chaos could be that there are insufficient good cells in the right place to assimilate a large amount of information properly.

From this we can see that the question as to what makes dyslexics’ brains special is as yet inconclusive.

Question 2: What is the origin of this special feature?

If there is something special about dyslexics’ brains, what is the origin of this speciality?

Here a distinction should be made between possible internal, i.e. relating to the body, and external or environmental issues.

Internal causes

It has been suggested that too much testosterone in the unborn child, or too great a sensitivity to it, could be responsible for the formation of ectopic cells and the characteristic size of the planum temporale in the brains of dyslexics. Testosterone is a male hormone, and it is well known that dyslexia is more common in boys than girls. Testosterone would have a negative effect both on the auto-immune system and on brain growth, particularly of the left hemisphere. In the New Zealand black mouse, an animal which is born with a defective immune system, ectopic cells are indeed found in the brain. It is possible that there is a connection between illnesses which are based on defects in the auto-immune system, such as allergies, asthma, diabetes etc, and dyslexia. But if there is a connection between the auto-immune system, the occurrence of ectopic cells and dyslexia, it is not yet fully understood.

In conclusion, it is possible that there is a connection between how the auto-immune system works and the occurrence of ectopic cells, and perhaps even between these two and dyslexia.

External causes

The quality of the brain is not dictated solely by the genes. The environment can improve or detract from the structure and function of the brain. When we talk about the environment, we mean the physical-chemical, physiological, psychological and social surroundings. The womb is the early environment for the child, and the family and school are learning environments, and it is known that they produce significant effects on the brain. It is quite possible that deviations in the structure and function of the brain are caused not so much by defective genes as by negative influences exerted by the environment on the brain.

The deviant symmetry of the planum temporale may be caused in the later stages of pregnancy and the early stages of childhood. During these phases of a child’s life there is usually a drastic selection among nerve cells. Millions of cells die off while those remaining grow to maturity. This may perhaps be due to an external reason. We know that environmental factors, including factors within the womb, act on a range of nerve structures.

The environment, particularly certain learning situations, can however produce positive effects, and therapeutic use can be made of this.

Question 3: How does this special feature manifest itself?

Scientific research has changed its focus on the manifestations of dyslexia over the years. About thirty years ago, attention was paid in particular to sight and motor variables which were thought to be connected with dyslexia. Some time later extensive research was carried out into so-called inter-sensory integration: if a word is to be read out loud, is it first seen visually and then spoken aloud? The question was whether dyslexic children have special difficulty with visuo-auditory integration. Because written words are ordered in space and spoken letters are ordered in time, the spatial-temporal integration was also examined. Later the view was adopted that the central problem with dyslexia is the processing of verbal information; it is not important in this connection whether the information is arranged in space or time.

Currently attention seems to be focused on the relationship between spoken and written language. Questions are directed to the nature and quality of phoneme-grapheme analysis of the script and the automation of the phonetic and orthographic coupling.

In considering current ideas on language awareness, it is even possible to say that nowadays we have ‘left language behind.’ What do we mean by language awareness? Take the word ‘motorway.’ A dyslexic person can pronounce such a word as well as anyone else but, with a little thought, the non-dyslexic is aware that the one word consists of two recognisable groups of letters, ‘way’ and ‘motor.’ The question is whether the dyslexic learner also possesses such an awareness of language.

Other questions go unanswered. For example: Do dyslexics understand the message of the text correctly? Do they understand what they read? Do all dyslexics face the same problems here or are there dyslexics and dyslexics? In other words, is dyslexia a homogeneous or heterogeneous phenomenon?

In my own view, there are different types of dyslexia, and they require different types of treatment.

Behaviour manifested with dyslexia
Behaviour manifested with dyslexia in the earlier and later stages

Research tells us that dyslexia can be accompanied by social and emotional problems. Dyslexia and learning difficulties in general can lead to emotional insecurity and social isolation. It is a good idea to define these concepts, for example, by asking such questions as: How many friends do they have? What are their career prospects? What kind of mood do they generally exhibit? If they have physical complaints: How many are there? How do they perform in further education?

Question 4: What intervention is appropriate?

Before a treatment can be called a treatment, it must be proved that it produces positive effects. The positive effects of a treatment must be clearly indicated and its limitations recorded. If, after a treatment is used for the first time, a child shows improvement in reading and spelling, this does not necessarily mean that the treatment has worked. A great deal of research is necessary before a treatment can be called a treatment.

The nature of treatment, intervention and prevention will be determined to an important extent by the theory and research to date. For example, if it were proved that testosterone had a role, during the prenatal period, in causing dyslexia, prevention would be the course to take.

When one intervenes with the treatment at the level of the brain, given that it can actually be done, there are several ways of proceeding. If, for example, we have developed and tested a model based on the relationship between the reading and learning processes on the one hand and control by the hemispheres on the other hand, we can – using our knowledge that brains are sensitive to stimulation – try to involve the other hemisphere more in the reading and learning processes.

In schools where children with dyslexia are taught, it seems that the teachers who work most competently are those who are open-minded to new scientific research. As more students with special educational needs are being accommodated in mainstream schools, teachers are working in accordance with policies on integration. In my opinion, the following steps should be taken to make this integration successful:

• Educationalists in regular or special education should be made more aware of, and become better acquainted with, research into learning disability and dyslexia. They must be able to recognise a case of dyslexia and know how to refer it. This should be the case for teachers in primary, secondary and higher education.
• In each school or group of schools there should be a specialist, such as an educational psychologist, who is responsible for diagnosing dyslexia, stating what type it is, and treating it. This requires extensive knowledge and specific skills. The specialist must be able to evaluate his findings critically and communicate them. He must be able to distinguish what has been proved from half-truths. He must also be able to pass on information horizontally to the class teacher and communicate vertically with a specialist scientific body or institution where the latest research findings will be available. Cases could be discussed at this institution and difficult cases could be referred there for treatment. He should also be familiar with other approaches, including those that rely on more than one type of know-how and treatment.

If this model were followed, a direct line of contact would be established between the educationalist in the school right through to the specialist scientific institution. The specialised member of staff in the school, who would liaise with the outside specialised scientific institution, should be an educational psychologist specialised in the subject or a qualified special-education teacher.

Alternatively, the school could choose a specialist from outside, for example from a specialised team based in the local education authority. The school-based teachers could then act with the specialised team and contact could be maintained with the scientific institution to keep up-to-date with the latest research, consult, and make referrals.