Aastha Somani - Research Intern
Dyslexia is primarily associated with a core speech sound (phonological) deficit (inability to translate letters and letter patterns into phonological forms), with additional impairments in naming speed and working memory.
People with dyslexia particularly show dysfunction in certain specific neural networks which relate to reading.
The functional Magnetic Resonance Imaging (fMRI) studies reflect the functional and structural abnormalities in the left parietal and temporal areas involved in phonological processing.
People with dyslexia compensate for this abnormality with engagement of the right side regions of the brain.
This explains the reading difficulty, inability to mentally represent words, inability to break down big words and entities into discrete sounds. (Moreau and Waldie, 2016)
Attention Deficit Hyperactivity Disorder (ADHD)
Attention Deficit Hyperactivity Disorder (ADHD) is characterized by excessive activity, short attention span and impaired inhibitory control.
ADHD also affects specific neural networks which control the working memory, planning, sustained attention, inhibition and interference control.
As the name suggests, it is divided in two components: inattention and hyperactive compulsive
Neuroimaging studies show an overall decreased function in the prefrontal cortex (region of the brain controlling motor function) and basal ganglia (behaviour and emotion centre of the human brain) and dysfunction due to imbalance of neurotransmitters such as dopamine, epinephrine, norepinephrine and serotonin. (Moreau and Waldie, 2016)
Comorbidity of Dyslexia and ADHD
Studies suggest 30-50% of the time, dyslexia and ADHD occur simultaneously (Sahoo, Biswas, and Padhy, 2015; Moreau and Waldie, 2016)
Although functionally the two conditions may be different, their underlying mechanisms are similar, suggesting that they are due to similar congenital neurological pathologies.
Both the conditions share common cognitive deficits like speed processing and studies narrow down to a common genetic influence.
Variation in common neural mechanisms between both disorders is observed by neuroimaging studies in diagnosed individuals.
Heritability estimates - Dyslexia: 40-60% and ADHD: 70-80%
Both the conditions are studied to be polygenetic, meaning that the cumulative effect of many genes together causes them.
The overlap between certain gene linkage regions explains the idea of a single gene responsible for both conditions.
However, genetic factors do not entirely because of the conditions, environmental factors are also at play.
Also, due to the overlap between risk factors of both the conditions, phenotypically that is physical, we observe similar symptoms, which proves co-occurrence of the two disorders.
Early Diagnosis and Interventions:
With advanced knowledge of the subject today, diagnosis is earlier and better.
One most common way to diagnose the above-mentioned conditions is to notice the physical (fine motor movements like the grip of a pen in case of dyslexia) or behavioural (like mood swings, anxiety etc.) changes in an individual.
However, a different and promising way of diagnosis now includes Neuroimaging to study the areas of dysfunction in the brain.
These dysfunctioning regions are identified and targeted for therapy, wherein the original function may or may not be restored.
On the other hand, the brain may carry out the original function but not by activating the same region of the brain. Rather, a compensatory neural circuit can be seen functioning.
This is a property of the neural circuits of the brain, called neuroplasticity, where the brain alters certain pathways on extensive and repetitive interventions.
It is observed to occur much more efficiently at younger ages, which is why earlier diagnosis (first 3 years) and immediate treatment is more effective.
It is a critical period of development and hence manipulations are easier compared to that in a mature and developed brain network.
Moreau, D., & Waldie, K. E. (2016). Developmental Learning Disorders: From Generic Interventions to Individualized Remediation. Frontiers in psychology, 6, 2053. https://doi.org/10.3389/fpsyg.2015.02053
Sahoo, M. K., Biswas, H., & Padhy, S. K. (2015). Psychological Co-morbidity in Children with Specific Learning Disorders. Journal of family medicine and primary care, 4(1), 21–25. https://doi.org/10.4103/2249-4863.152243