Is dyslexia associated with circadian dysfunction?

[NinaMS]

​Potentially circadian medicine offers a holistic way of bringing together a number of symptoms that may on first sight seem unrelated. Disruptions in circadian systems can negatively affect sleep quality, alertness, cognitive performance, motor control, metabolism, etc. Increasingly it is being recognised that this approach can be applied to specific learning difficulties.

 

A growing body of research has identified significant sleep problems in children with autism. Disturbed sleep–wake patterns and abnormal hormone profiles in children with autism suggest an underlying impairment of the circadian timing system. G Glickman 2010. Z Yang 2015

 

Sylvie Tordjman (et al Feb 2015) proposes a central role of rhythmicity and synchrony of rhythms in typical child development and offers an integrative approach, which considers autism as a disorder of biological and behavioral rhythms.

 

Similar observations have been made in relation to ADHD. It is not clear how sleep disturbances come to be so common in ADHD, but one putative mechanism is through the circadian timekeeping system. A N Cogan 2016. I Paclt 2011.

 

It would also be interesting to explore whether this approach could be applied to dyslexia. Common problems with dyslexia include with tendencies to 'zone out' and lose track of time. They also include:

 

1. Problems with writing and motor skills

 

It has been found that there are circadian rhythms in handwriting. I Jasper 2009.

 

Dyslexia has also been associated with dyspraxia, differences in eye movement and binocular vision/depth perception.

 

There are circadian rhythms of motor function, including rapid eye movement. S W Wurts 2000. L Zhou 2014.

 

A link between motor dysfunction and circadian rhythms has also been associated with autism Sylvie Tordjman (et al Feb 2015). And in an animal model, it was recently shown that circadian disturbances that exist before parkinson's onset dramatically worsen motor and learning deficits brought on by the disease.

 

Differences in gamma oscillations have also been detected in dyslexia (e.g K Lehongre - ‎2013 ) and a number of other neuro-conditions. Interestingly gamma oscillations have been very closely associated with rapid eye movements called microsaccades. Invasive recordings in a number of animal species suggest that these oscillations play a key role in such diverse processes as visual feature integration, attentional selection, episodic memory and working memory maintenance. K Wieczorek 2015.

 

The presence of gamma-band activity in many LFP measurements under stimulation led to the idea that gamma-band oscillations serve as a ‘clock’ signal for the purpose of temporally encoding information (Hopfield, 1995; Buzsaki and Chrobak, 1995; Jefferys et al., 1996; Buzsaki and Draguhn, 2004; Buzsaki, 2006; Bartos et al., 2007; Fries et al., 2007; Hopfield, 2004). The ‘clock’ theory of gamma combined with the pervasiveness of gamma oscillations have given rise to the theory that the brain uses gamma oscillations to synchronize different regions of the brain for the purpose of ‘binding’ information about a stimulus (Gray and Singer, 1989; Singer and Gray, 1995).

 

2. Problems with the rhythms of speech and learning language

 

Scientists have identified that dyslexics have problems with the rhythms of speech. ' children with dyslexia often find it difficult to count the number of syllables in spoken words or to determine whether words rhyme. These differences are seen across languages with different writing systems and they indicate that the dyslexic brain has trouble processing the way that sounds in spoken language are structured' M Huss 2011.

 

It has been found that generally, there are optimal times in the day for learning other languages (suggesting circadian rhythms influence language learning) Kees De Bot 2015, and may influence language performance. J Rosenberg 2009.

 

It is also speculated that there may be differences in dyslexia and other specific learning difficulties in circadian driven mechanisms which protect the ear from noise. During the day a hormone called brain-derived-neurotrophic factor (BDNF) is distributed into the ears. This hormone protects the auditory nerves from damage. It provides a layer of insulation to protect the ears from harmful noises that are more likely during waking or day hours. This mechanism is based on circadian rhythms.

 

3. Problems with memory (particularly sequential task information)

 

The presence of circadian variations in gene expression and synaptic plasticity in hippocampal cells, as well as in learning and memory formation, indicates an inherent link between cellular activities and behaviors of the whole animal. However, the mechanism by which the activity of a group of pacemaker cells is translated into behavioral responses is still poorly understood. X Mou 2016.B L Smarr 2014

 

4. Sleep Problems

 

Some adult dyslexics report sleep dysfunction. http://community.dys...exics-and-sleep. This could be due to stress, but a recent study has connected sleep disorder and development dyslexia. Acta Paediatr. 2016

 

This could potentially be related to melatonin. It should not be assumed that it is due to underproduction of melatonin, as dyslexic people report high levels of tiredness and vivid dreams which are more symptomatic of over production of melatonin. However, it has also been reported that dyslexia is a 'changeable' conditions, and this condition may fluctuate.

 

5. The perceived benefits of different lighting and fish oils for people with dyslexia.

 

It has been suggested that dyslexic people can find their symptoms mitigated by filtering out certain types of light (including blue), although the research on this has been inconclusive.

 

Circadian rhythms can be entrained by various means including nutrition, temperature, but also lighting. For example it has been found that in the general population blue light improves performance generally due to circadian rhythms. J Sharples 2007 . However dyslexics may be over sensitive to blue light because of differences in circadian rhythms. These may be because of differences in retinal receptors e.g G S Grosser 1998.

 

'Recently, a new class of intrinsically photosensitive retinal ganglion cells (IPRGCs) has been discovered. These connect to the body’s internal clock, which controls diurnal rhythms. Thus, the function of its input from the melanopsin-containing retinal ganglion cells is not to mediate conscious vision but to synchronise the SCN to seasonally varying day length.... it has been reported that 'Many children with visual reading difficulties have disturbed sleep patterns Their parents are often surprised that the blue filters seem to improve their child’s sleeping. Likewise, many such children complain of headaches when they try to read. Migraine headaches are known to be accompanied by disturbed sleep rhythms. Hence, we now have many anecdotal reports that successful treatment of reading difficulties with blue filters is accompanied by fewer headaches, and we are now following this up more systematically'. J Stein 2014.

 

Recent research in animal models suggests PUFA-deficient diet lessens the melatonin rhythm, weakens endogenous functioning of the circadian clock, and plays a role in nocturnal sleep disturbances as described in attention deficit/hyperactivity disorder. The circadian clock plays a role in regulation of plasma and tissue lipids, including triglycerides, cholesterol and free fatty acids.

 

6. Related immunological Issues

 

Immunological disorders are frequently found in people with specific learning difficulties. The human immune response also follows a circadian cycle (Levy et al.,1991) and most immune cells express circadian clocks and present a wide array of genes expressed with a 24 hr rhythm, and alterations in circadian rhythms lead to disturbed immune responses. N Labrecque 2015

 

Some Possible Solutions

 

Please note that I am not a medical professional or chronobiologist. I am however dyslexic and so interested in a holistic approach to understanding this condition.

 

'If it is' found that dyslexia and other specific learning difficulties are related to circadian rhythms then there are some possible solutions.

 

Melatonin treatments are not a simple answer and there is limited evidence of their effect on people with specific learning difficulties. Over production of melatonin can also have serious side effects. There are however various ways of naturally entraining the circadian clock e.g through light exposure, temperature, nutrition (K Peukuri 2011). Due to the link between circadian rhythms and the metabolism, chrononutrition is emerging as a key form of intervention is addressing circadian dysfunction (e.g J D Johnston 2016).

 

There can also be consideration of equipment that effect circadian rhythms such as blue screens on computers and mobile phones, and use of stimulants such as coffee.

 

It will also be important for educators to recognise the influence of circadian rhythms in the learning environment (and recognising these may be different for some students).