Summary – Recent research by the DRT and others has suggested that magnocellular (M) neurones in the brain play an important role in reading and that M- deficits contribute powerfully to reading problems because the M system is so crucial for directing visual and auditory attention and eye movements to letter and word features and sounds during reading. These nerve cells are called magnocells because of their noticeably large size; this equips them for rapid signalling, timing events and tracking changes. Anatomical, electrophysiological, psychophysical and brain imaging studies all concur that these nerve cells develop slightly abnormally in dyslexic brains.
The main aim of DRT research into visual and auditory weaknesses in poor readers is to develop treatments that will help them and prove by randomised controlled trials that they work. Simple treatments such as blue or yellow coloured filters or musical training really can help dyslexics to learn to read. Then we aim to persuade Policy makers to make them available to all those with reading problems. If we can do these things we should be able to save thousands of children from the loss of self confidence, shame and misery that reading failure so often brings in its train.
Reading is actually very difficult, the most difficult skill that most people are expected to acquire. You need to be able to identify each of a line of small visual symbols where tiny details make all the difference (eg b,d,q,p), then put them in the right order, then translate them into their sounds, and only then can you decide what the word means. At the same time you have to build up a background knowledge of how words can be split down into their individual letter sounds (phonology). To make matters worse English is littered with exceptions to the letter-sound rules. Compare bough, dough, lough, cough, enough! After all that effort on reading each word many children can’t remember the words they read at the beginning of the sentence to understand the whole thing.
So it is really amazing that 2/3rds of children of all levels of intelligence actually do learn to read so fluently, and perhaps it is not so surprising that 1/3rd of children leave school unable to read properly. But this is not only an appalling waste which costs the country £2 billion per year in terms of additional teaching, truancy, school exclusion, unemployment, drug addiction and crime4, but it is a most potent cause of misery.
The children lose all self-confidence and hope. Because literacy is so important in the modern world, they can only look forward to a life of depression and failure. Or their anger and frustration may lead them into aggression and crime. Yet if they survive their schooling, many dyslexics can become remarkably successful. Prof John Stein, a medical tutor at Magdalen College Oxford, was introduced to children’s reading problems by a very wise orthoptist, Sue Fowler. He found that, like patients with cerebellar damage whom he’d been researching for many years, many could not hold their eyes steady, so that letters seemed to wobble, move around and cross over each other. These wobbles represent a mild form of oscillopsia that is often seen in cerebellar patients. You can’t visually identify letters and their order if they’re moving around all the time (try reading when very drunk!).
In cerebellar patients he had shown that their unstable vision was due to damage to large nerve cells in the brain, known as visual magnocells, that are specialised for detecting movement. When these magnocells are not working properly the servo system that keeps your eyes fixed on a letter fails, and so the letters appear to move around. So with Sue he set up a clinic to investigate whether children’s visual reading problems were due to the same cause. Sue & John were able to show that many dyslexics do indeed have impaired development of these magnocells (though not as seriously as in cerebellar disease), because the cells move into the wrong positions and make the wrong connections during the early development of the brain; this explains why many dyslexics’ vision is so unstable. They found that in everybody the quality of their visual magnocellular function plays a very important role in how well they can acquire the visual skills required for reading. Even though letters don’t move, the eyes do; so a person’s sensitivity to moving visual stimuli predicts his skill at identifying the visual order of letters and the visual form of words – their ‘orthography’.
Olive Meares in Australia was the first to suggest that children with visual reading difficulties can see print more easily through certain coloured filters. This was taken up commercially in the USA and UK. But these systems require that each child is individually prescribed a special colour; so the glasses tend to cost a lot! However since the visual magnocellular system is mainly influenced by just yellow and blue light, we argued that these are the only two colours that will really make much difference.
Skiers in a ‘whiteout’ know that yellow goggles can make things look brighter and more contrasty. This is because yellow enhances their visual magnocellular input. Thus we’ve recently confirmed in a small double blind, randomised control, trial that in suitable children simple and cheap deep yellow filters can help them to improve their reading very significantly. We are carrying out a much larger trial now to try to convince the sceptics.
Blue filters can be even more effective. They probably work in a different way; because blue can affect the brain unconsciously. From the grainy two-dimensional images that are projected onto our retinae, and projected to the visual cortex via the retino-geniculate pathway, the brain creates a conscious vivid and detailed three-dimensional visual experience. But blue supplies other important pathways running from the eyes deep into a primitive part of the brain called the hypothalamus that cause powerful physiological and cognitive effects that we are hardly aware of. Unlike the light stimuli that determine our conscious perceptions, the visual projections to the hypothalamus cause responses that can long outlast the period of light exposure. Consequently, wearing blue filters for relatively short periods can have persistent effects on our health and cognitive functions for hours or even days afterwards. About half of all the children with reading problems that we see can be helped simply by wearing either yellow or blue filters.
The blue input to the hypothalamus helps to entrain the body’s internal clock according to seasonally changing day length in order to increase magnocellular activity during the day and decrease it at night. Thus blue light increases alertness both during the day and the night; and it reduces the drowsiness that occurs at night. Bright blue light can also improve auditory attention, suggesting that the effects of light on alertness and attention are not mediated by the system responsible for conscious visual perception. Rather they seem to be mediated by the retino-hypothalamic system that starts with a newly discovered set of receptors in the retina, the ‘melanopsin containing ganglion cells’.
Melanopsin retinal ganglion cells and their projections (melanopsin RGCs)
Photosensitive pigments located in the retina translate light into electrical activity. Most photopigments are located in the retinal rods and cones, rather than in ganglion cells. But recently it was discovered that some retinal ganglion cells are themselves photosensitive, the melanopsin RGCs. The melanopsin responds most strongly to deep blue light (475 and 485 nm). These RGCs are spread diffusely forming a photoreceptive net that samples the whole retina. They project strongly to the ‘biological clock’, the suprachiasmatic nucleus (SCN) in the hypothalamus, which controls the body’s diurnal rhythms. This retinohypothalamic tract (RHT) input synchronises this clock to seasonally changing day length to maintain the correct phase relationship between daylight and the biological rhythms of endocrine, physiological and cognitive activity.
Coloured filters, either worn as spectacles or used as overlays, have been successfully employed in the treatment of dyslexia for many years but there is no agreement about how they work. Bright blue light increases the activation of the parts of the brain involved in directing attention, such as the posterior parietal cortex. Abnormal function in these attention-modulating parts of the brain has been implicated in the pathogenesis of dyslexia. It is therefore likely that blue light selected optimally to recruit melanopsinRGCs will have the greatest effect on improving alertness and concentration and may therefore be the best for remediating the impaired attentional responses seen in dyslexia. The DRT has carried out a randomised control trial that showed that in suitable dyslexic children, wearing blue filters for 3 months improved their reading age by an amazing 9 months.
Blue light therapy has also been shown to help people with sleeping problems, to improve alertness during night shift work and to help overcome jet lag. This probably also works on the suprachiasmatic nucleus to alter the timing of diurnal rhythms. We found that children whose reading benefitted from wearing blue filters during the day often reported also that their sleeping patterns had improved, and we showed that this was probably due to an effect on the SCN; at night secretion of the sleep hormone, melatonin, which is also under the control of the SCN, can be inhibited by just 15 minutes of blue light ie blue light can reset the SCN rhythms to improve sleeping.
The effects of blue light on migraine
Likewise we found that in these dyslexics, who often complain of migraine type headaches, the blue filters often improved their headaches. Migraine was previously thought to be due to swelling of the arteries in the membranes surrounding the brain, the meninges. But we now believe that the hypothalamus and specifically the SCN is responsible. Blue coloured filters, worn as spectacles, have been found to be highly effective in reducing the frequency of migraine symptoms. So our blue filters are also efficacious in reducing migraine.
Seasonal affective disorder (SAD) is a depressive syndrome experienced by around 5% of the population, the symptoms of which recur in winter and autumn. A number of experimental findings combined with the circannual pattern of symptom expression implicate disordered diurnal rhythms controlled by the SCN in the pathogenesis of SAD. SAD symptoms are likely to be the result of an abnormal phase-delay in the circadian rhythm. Hence exposure to blue light, particularly in the morning, often improves SAD greatly.
Exposure to natural daylight at work and school is often minimal and fluorescent electric lighting is usual. Unfortunately most fluorescent lights radiate very little short wavelength blue light. Full spectrum fluorescent lights, the spectral output of which is similar to that of natural daylight, or blue light, should therefore be better for human health and cognitive function because they stimulate the retinal hypothalamic system more effectively.