It appears that the majority those with reading disorders likely struggle due to structural disorganization and functional impairment of the temporal-parietal juncture in the left hemisphere. This is the region of the brain responsible for phonological processes (e.g. accurately perceiving and manipulating speech sounds within words including tasks such as rhyming and segmenting). While the vast majority of those with dyslexia struggle with reading due to deficits in phonological processing, reading development can also be disrupted by impairments in other neuro-cognitive processes including rapid naming, orthographic processing, working memory, and executive functioning. Each of these on their own, or in combination with one another, produce different subtypes of reading disorders.
Because there are different subtypes of reading disorders, a one size fits all approach to assessment is inadequate for identifying and accurately describing the nature of students’ reading difficulties. Without first understanding the nature of a child’s reading disorder, any attempt to develop a program for remediating skills deficits amounts to a shot in the dark. Below are the four subtypes of reading disorders along with a description of the defining characteristics and associated brain regions.
Dysphonetic Dyslexia – Impaired ability to sound out words due to deficits in phonological processing resulting in an overreliance on remembering the way words look or using context clues to guess at what words might be. Dysphonetic dyslexia is associated with impaired functioning in the temporal-parietal regions in the left hemisphere and is the most common form of dyslexia. Perhaps as many 80% of children with developmental reading disorders have a dysphonetic dyslexia.
Orthographic or Surface Dyslexia – Impaired ability to efficiently recall the way words look due to deficits in orthographic processing and/or rapid automatic naming. These individuals, who may have adequate phonological processing, over rely on sounding out words because they never develop automaticity in word recognition. Their reading is characteristically slow and laborious and they have significant spelling difficulties, particularly words with irregular spellings. Neuroanatomical deficits likely lie in the visual word form area in the fusiform gyrus of the left hemisphere.
Mixed Dyslexia – Severe reading difficulties stemming from deficits in both phonological and orthographic processing deficits. Impaired functioning in multiple brain regions likely exist including the temporal-parietal regions, angular gyrus, and fusiform gyrus.
Comprehension Deficits – For some children, their basic reading skills are intact but their ability to comprehend text is severely impacted. This is often due to deficits in working memory and executive functioning (dorsolateral prefrontal cortex) impacting the child’s ability to remembering and organize information in their active awareness.
At Bylund Neuro-Educational Services we take great pride in conducting thorough dyslexia evaluations in order to identify not only whether or not a reading disorder is present but also identify the subtype of reading disorder and the types of interventions that are most likely to produce the best results. If you know or suspect your child has a developmental reading disorder (i.e. dyslexia), call Dr. Bylund today for information on obtaining a thorough evaluation and proper diagnosis.