Dyslexia Demystified: Understanding the Neurological Basis

According to the British Dyslexia Association, over 6 million people in the UK have dyslexia and may not have received a diagnosis.

Dyslexia is a specific learning disorder characterised by difficulties with accurate or fluent word recognition, difficulty decoding and difficulty spelling. These challenges are not due to lack of intelligence, sensory impairments or inadequate educational opportunities. Dyslexia is considered a part of neurodiversity; a concept that embraces a variety of brain differences, including those related to conditions such as dyslexia, attention deficit hyperactivity disorder (ADHD), autism, and other neurological variations. This perspective recognises that these differences are natural variations of human cognition rather than deficits or disorders.

Dyslexia is often identified in childhood, but its effects can persist into adulthood.

The key characteristics of dyslexia include:

• Having trouble with reading words in isolation, slow reading, and difficulty in recognising common words by sight.
• Struggles with sounding out words (decoding), particularly unfamiliar ones.
• Frequent misspellings and difficulties with spelling patterns and rules.
• Problems with recognising and manipulating sounds in words.
• Understanding what is read can be challenging, particularly as a result of slow and effortful reading.

The causes and risk factors of dyslexia can include:

• Genetic factors – dyslexia often runs in families, indicating a genetic component.
• Brain differences – research shows that individuals with dyslexia have differences in the structure and function of certain brain areas related to language processing.
• Environmental factors – while less influential, environmental factors like limited exposure to language and reading in early childhood can exacerbate reading difficulties.

Dyslexia is diagnosed through a series of evaluations by educational psychologists, speech-language pathologists or other professionals. These evaluations assess reading skills, language processing, cognitive abilities and educational history. There is no cure for dyslexia, but early intervention can significantly help.

Advancements in neuroimaging and cognitive neuroscience have provided significant insights into how the brain of a person with dyslexia functions differently from those without the disorder. By exploring the neural mechanisms that contribute to dyslexia, we can better understand its causes, which range from genetic predispositions to anomalies in brain structure and function. This exploration not only helps in early identification and intervention but also paves the way for the development of more effective, personalised approaches to treatment and support for individuals with dyslexia.

Neurological Basis of Dyslexia

Brain Structures Involved

Reading and language processing involve multiple interconnected areas of the brain, particularly in the left hemisphere.

• The left hemisphere of the brain is typically dominant for language processing in most people, including tasks related to reading, writing, speaking and understanding language.
• Broca’s area is located in the left frontal lobe. Broca’s area is crucial for speech production and grammatical processing. Damage to this area can result in Broca’s aphasia, characterised by slow, laborious speech with relatively good comprehension.
• Wernicke’s area is found in the left temporal lobe. Wernicke’s area is essential for language comprehension. Damage to this region can cause Wernicke’s aphasia, where speech is fluent but nonsensical, and understanding of spoken language is impaired.
• The occipital lobe is located at the back of the brain and is primarily responsible for visual processing. When reading, the visual cortex within the occipital lobe processes the shapes of letters and words.
• Visual Word Form Area (VWFA) is situated in the left occipitotemporal region. The VWFA is a specialised area that recognises written words and letter patterns, helping in the quick identification and processing of written language.
• The temporal lobe is located on the sides of the brain. It is heavily involved in processing auditory information, including the sounds of language. The primary auditory cortex within the temporal lobe decodes the sounds of speech.
• The angular gyrus is located at the junction of the parietal, occipital, and temporal lobes. The angular gyrus plays a role in various language-related tasks, including reading comprehension, number processing, and even the ability to associate words with their meanings.
• The supramarginal gyrus is situated in the parietal lobe, adjacent to the angular gyrus. This area is involved in phonological processing (the sound structure of language) and also contributes to reading and writing.

The arcuate fasciculus is a bundle of nerve fibres that connects Broca’s area and Wernicke’s area, allowing for the integration of speech production and comprehension. Damage to this pathway can result in conduction aphasia, where a person may understand language and speak relatively well but struggle with repetition and producing coherent speech.

These brain areas work together in a highly coordinated manner to enable the complex tasks of reading, understanding, speaking and writing language. The left hemisphere is particularly crucial for these functions, with the occipital lobe handling visual aspects of reading, the temporal lobe processing auditory information and comprehension, and various specialised regions like Broca’s and Wernicke’s areas orchestrating language production and understanding.

Neurobiological Factors

Dyslexia has a strong genetic component, with studies suggesting that it is highly heritable. Family and twin studies have shown that the likelihood of a child developing dyslexia is significantly higher if a close family member has the disorder.

Several genes have been implicated in dyslexia, although the disorder is polygenic, meaning that multiple genes contribute to the risk. Some of the most studied genes include DCDC2, DYX1C1, KIAA0319, and ROBO1. These genes are involved in brain development, particularly in areas related to language and reading.

Dyslexia is associated with atypical brain development, particularly in regions involved in reading and language processing. Structural imaging studies have shown differences in the size and shape of certain brain areas, such as the left hemisphere’s temporoparietal and occipitotemporal regions, which are crucial for phonological processing and visual word recognition.

While genetics play a crucial role, environmental factors can influence the expression of dyslexia. For example, early exposure to a rich language environment and effective educational interventions can mitigate some of the challenges associated with dyslexia.

Functional MRI and Brain Imaging

Neuroimaging studies have provided significant insights into how brain activity differs in dyslexic individuals during reading tasks compared to typical readers. 

Dyslexic individuals often show reduced activity in the left hemisphere, particularly in areas known to be critical for reading. These include the left inferior frontal gyrus, the left parietotemporal region (involved in phonological processing), and the left occipitotemporal region. These areas are typically involved in processing phonological information, mapping letters to sounds, and recognising written words. In dyslexic readers, underactivity in these regions is associated with difficulties in these processes, leading to challenges in decoding and recognising words.

Some dyslexic individuals show increased activity in the right hemisphere and in more anterior regions, such as the right frontal lobe. This is thought to reflect compensatory mechanisms, where the brain tries to make up for the underactivity in the left hemisphere.

How Dyslexia Affects Language Processing

Phonological Processing

One of the key deficits in dyslexia is difficulty with phonological processing, particularly in the ability to process and manipulate phonemes. Phonemes are the smallest units of sound in a language, and they are crucial for understanding how words are constructed and for developing reading skills.

Phonological awareness is the ability to recognise and work with sounds in spoken language. For example, being able to identify the first sound in a word or being able to blend sounds together to form a word. Dyslexic individuals often struggle with this skill. They may find it hard to break down words into their constituent phonemes or to blend phonemes into words.

Phonological mapping is the process of linking phonemes to their corresponding letters or letter combinations. This skill is essential for reading and spelling. Dyslexia often involves a disruption in this mapping process, making it hard for individuals to connect sounds to the appropriate letters or to decode written words into sounds. Because of difficulties with phoneme processing, dyslexic individuals often read more slowly and with less accuracy than their peers. They may have to put considerable effort into decoding each word, which can make reading laborious and impact comprehension.

Dyslexic individuals may also have weaknesses in phonological memory, which is the ability to remember sequences of phonemes. This can affect their ability to retain the sounds of words long enough to decode them, or to hold on to information they have just read.

Orthographic Processing

One of the key challenges for individuals with dyslexia is orthographic processing. Orthographic processing refers to the ability to recognise written words and the correct sequences of letters in words, which is essential for fluent reading and accurate spelling.

Dyslexic individuals often struggle to recognise words quickly and accurately. Unlike typical readers who can recognise words by sight, dyslexic individuals may need to decode each word letter by letter, making reading slow.

Orthographic processing involves the ability to remember and reproduce the correct sequence of letters in words dyslexic individuals often have trouble with spelling. They may frequently misspell words, omit letters or confuse the order of letters.

English has many words that do not follow standard phonetic rules. Dyslexic individuals often have more difficulty with these irregular words because they rely heavily on phonetic decoding strategies, which do not always apply. Dyslexic people often have difficulty storing and recalling the visual forms of words. This weakness in visual memory contributes to challenges in recognising familiar words quickly and in learning new words.

Dyslexia can affect an individual’s ability to retrieve the correct word from memory, especially under time pressure. This can make reading and writing slower and more effortful. Due to challenges in orthographic processing, dyslexic readers may frequently substitute, omit or transpose letters when reading. This can make it difficult to comprehend text, as the meaning of sentences may be altered by these errors.

Working Memory and Executive Functioning

Working memory is a crucial cognitive system that temporarily holds and manipulates information necessary for various complex tasks, including reading comprehension. It involves several components, with the phonological loop, the visuospatial sketchpad, and the central executive playing significant roles.

• Phonological loop – this component is responsible for processing and storing verbal information. When reading, the phonological loop helps in retaining the sounds of words and sentences, allowing the reader to connect words and phrases, understand their meaning, and integrate them into a coherent narrative.
• Visuospatial sketchpad – this component handles visual and spatial information. In reading, it helps in visualising the text, understanding the layout of information, and forming mental images that correspond to the narrative or content.
• Central executive – this component manages and coordinates the activities of the phonological loop and visuospatial sketchpad. It is involved in focusing attention, organising information and integrating new information with existing knowledge, which are all essential for comprehending and retaining what is read.

Many individuals with dyslexia have a reduced working memory capacity, especially in the phonological loop. This limitation makes it difficult to hold multiple pieces of information in mind simultaneously, which is necessary for understanding long or complex sentences, integrating new information with prior knowledge, and maintaining coherence in reading. The central executive in working memory is crucial for focusing attention, selecting relevant information and suppressing distractions. Dyslexia can involve impairments in these executive functions, leading to difficulties in maintaining attention on reading tasks, organising information and shifting attention between different aspects of a text.

Current Research and Advances

Ongoing Studies

Recent research into the neurological basis of dyslexia has provided valuable insights into how the brain processes language and why certain individuals struggle with reading and writing. 

Functional MRI (fMRI) studies consistently show that dyslexic individuals often exhibit under-activation in the left temporoparietal cortex, an area involved in phonological processing. There is also reduced activity in the occipitotemporal regions, which are critical for visual word form processing. 

A leading theory in dyslexia research suggests that there is a core deficit in phonological processing. Recent neuroimaging studies have reinforced this view, showing that dyslexic individuals have difficulties with tasks that require phonological awareness, such as rhyming or segmenting sounds within words, which is reflected in the brain’s reduced activation in relevant areas.

Some researchers are also investigating the role of rapid auditory processing deficits in dyslexia. The ability to process quickly changing sounds (such as differentiating between similar-sounding phonemes) is impaired in many dyslexic individuals, and this has been linked to differences in brain activity within the auditory cortex.

Neuroimaging studies have shown that targeted reading interventions can lead to changes in brain activity patterns in dyslexic individuals. For instance, after intensive phonological training, some dyslexic readers show increased activation in left hemisphere regions that were previously underactive, suggesting a degree of neural plasticity.

Emerging research is exploring whether neurofeedback or non-invasive brain stimulation techniques, like transcranial magnetic stimulation (TMS), can modulate brain activity in ways that might alleviate dyslexia symptoms.

Some studies have focused on the role of multisensory integration in dyslexia, examining how the brain combines visual and auditory information during reading. Dyslexic individuals often have difficulty integrating these sensory inputs, which is reflected in altered connectivity between relevant brain regions.

Research suggests that dyslexia may involve difficulties with cross-modal processing, where the brain integrates information from different sensory modalities. This dysfunction is linked to abnormal neural activation patterns in multisensory regions of the brain.

As our understanding of the neurological basis of dyslexia deepens, there is growing interest in developing personalised intervention strategies. For instance, identifying specific neural profiles or genetic markers might help tailor interventions to individual needs.

Ongoing research is increasingly focusing on how the brain’s reading network develops over time in both typical and dyslexic individuals. This could lead to earlier identification and intervention strategies, potentially mitigating the impacts of dyslexia before they fully manifest.

Technological Innovations

Advancements in brain imaging and neuropsychological testing have significantly deepened our understanding of dyslexia. 

• Functional MRI (fMRI) – fMRI has been instrumental in revealing the neural mechanisms underlying dyslexia. It allows researchers to observe brain activity in real time while individuals engage in reading tasks. Studies have shown that people with dyslexia often exhibit reduced activity in brain regions associated with phonological processing, particularly in the left hemisphere, which is crucial for language processing.
• Diffusion Tensor Imaging (DTI) – DTI, a form of MRI that maps white matter tracts in the brain, has shown that individuals with dyslexia tend to have altered white matter pathways. These pathways are critical for the communication between brain regions involved in reading, such as the connection between the visual and language-processing areas.
• Magnetoencephalography (MEG) – MEG provides a millisecond-by-millisecond picture of brain activity, offering insights into the timing and sequence of brain processes during reading. Dyslexic readers show atypical timing in processing sounds and letters, which helps explain the difficulties in decoding words.
• Neuropsychological testing – neuropsychological tests assess various cognitive functions, such as phonological awareness, working memory and rapid naming. These tests help identify specific deficits in dyslexic individuals, such as difficulties in processing phonemes, which are crucial for decoding words.

Combining neuropsychological tests with brain imaging data allows for the early identification of dyslexia. For instance, children who show atypical brain responses to language stimuli, combined with poor performance on phonological tests, are at higher risk for developing dyslexia. Early diagnosis can lead to more timely and effective interventions.

Neuropsychological testing can guide personalised interventions. By identifying specific areas of weakness, such as visual processing or working memory, educators and clinicians can design targeted remediation strategies that address the unique needs of each dyslexic individual.

The integration of brain imaging and neuropsychological testing has led to a more comprehensive model of dyslexia that links specific brain abnormalities to behavioural symptoms. For example, a reduced activation in the left occipitotemporal cortex correlates with slow and effortful reading in dyslexic individuals. This understanding helps clarify why certain interventions, like phonics-based instruction, are effective by targeting the specific brain circuits involved in reading.

Research using brain imaging has shown that effective interventions can lead to changes in brain function in dyslexic individuals. For instance, after intensive reading instruction, fMRI studies have shown increased activation in brain areas that were previously underactive in dyslexic children. This demonstrates the brain’s ability to reorganise and adapt in response to targeted interventions, highlighting the potential for improving reading skills even in individuals with dyslexia.

Advancements in brain imaging and neuropsychological testing have revolutionised our understanding of dyslexia by revealing the brain’s underlying structural and functional differences and by linking these differences to specific cognitive and behavioural profiles. These technologies not only aid in early diagnosis and the development of personalised interventions but also provide hope for improving outcomes through evidence-based educational strategies.

Implications for Intervention and Support

Educational Strategies

Teaching dyslexic students to read and write effectively involves using evidence-based approaches tailored to their unique learning needs. Here are some proven strategies and methods:

• Structured literacy – this emphasises explicit, systematic instruction in phonology, orthography and morphology. Key elements include phonemic awareness, involving teaching students to recognise and manipulate individual sounds in spoken words, explicit instruction in the relationships between letters and sounds to help students decode words, and fluency building to improve speed, accuracy and expression. You can also use teaching techniques to improve understanding of text, such as summarising and questioning.
• Multisensory instruction – this approach involves engaging multiple senses to help students connect sounds, letters and words. Visual uses colour-coded letters and words, and visual aids like pictures and charts. Auditory incorporates listening activities and repetition. Kinaesthetic uses hands-on activities like writing in sand or using letter tiles.
• Assistive technology – tools and software can provide additional support, e.g. text-to-speech software converts written text into spoken words, helping with comprehension. Speech-to-text tools allow students to dictate their writing, which can be easier than typing or handwriting. Reading apps provide interactive reading experiences and phonics practice.
• Individualised instruction – tailoring instruction to the specific needs of each student can be very effective. Use regular assessments to identify specific areas where the student struggles and adapt instruction accordingly. Personalised instruction can address individual challenges more effectively than group instruction.
• Explicit vocabulary instruction – this focuses on teaching vocabulary in depth. It teaches specific words and their meanings directly.
• Repetition and practice – regular practice helps reinforce learning. Regularly revisit previously learned concepts to strengthen retention.

Having a positive attitude towards learning can improve outcomes. Emphasise the importance of effort and progress rather than just results, and praise the effort. Create a supportive environment where mistakes are viewed as part of the learning process.

Working with educational psychologists, speech-language pathologists and special education teachers can provide additional support and resources. Engaging families in the learning process can enhance effectiveness and provide families with strategies to support reading and writing at home. Keep open lines of communication between teachers and families to monitor progress and address concerns.

Adjust the curriculum and assessment methods to better suit dyslexic students. Use oral presentations or projects instead of traditional tests to assess understanding and adapt reading and writing assignments to match the student’s current level of proficiency.

Implementing these strategies with consistency and patience can significantly improve the reading and writing skills of dyslexic students.

Therapeutic Approaches

Cognitive and behavioural therapies tailored to dyslexia focus on addressing the specific challenges that individuals with dyslexia face in reading, writing and other language-related tasks.

Therapies for dyslexia aim to improve reading skills, boost confidence and manage any related emotional or behavioural issues.

Cognitive therapies for dyslexia include:

• Phonological awareness training – this is one of the most common cognitive approaches. It involves exercises that help individuals recognise and manipulate the sounds in words, which is crucial for reading, e.g. breaking words into syllables, identifying rhymes or practising sound-letter associations.
• Multisensory learning – cognitive strategies often use multisensory techniques, engaging visual, auditory and kinaesthetic-tactile pathways simultaneously to reinforce learning. For example, tracing letters while saying the corresponding sounds helps solidify the connection between letters and sounds.
• Cognitive remediation therapy – this approach aims to improve specific cognitive skills that may be weak in individuals with dyslexia, such as working memory, attention or processing speed. Techniques may include memory games, visual-spatial activities and tasks designed to enhance processing efficiency.

Behavioural therapies for dyslexia include:

• Behavioural interventions in the classroom – these strategies focus on modifying the learning environment to better suit the needs of students with dyslexia. This can include structured routines, clear and consistent instructions, and the use of positive reinforcement to encourage desired behaviours.
• Self-monitoring and self-regulation – behavioural approaches often teach individuals to monitor their own progress and behaviour. For instance, students might learn to set goals for their reading practice, track their progress and reward themselves for meeting their objectives.
• Cognitive-behavioural therapy (CBT) – while CBT is traditionally used for anxiety and depression, it can also be beneficial for dyslexia-related stress or anxiety. CBT helps individuals develop strategies to cope with frustration, manage stress and build self-esteem by challenging negative thoughts and replacing them with positive, constructive ones.

Support for Families

Understanding the neurological basis of dyslexia can significantly enhance how parents support their children as they can tailor their approach to better meet their child’s specific needs. Knowing that dyslexia is not a reflection of intelligence or effort, parents can set realistic expectations, focusing on their child’s strengths and incremental progress rather than solely on reading ability. 

Dyslexia is often accompanied by anxiety or low self-esteem due to difficulties in academic settings. Understanding that these struggles are neurologically based, parents can help their children by emphasising that dyslexia is just one aspect of who they are, and by celebrating their child’s other talents and achievements this can build self-confidence and reduce the stigma associated with the condition.

Knowing the specific neurological challenges of dyslexia can help parents communicate more effectively with teachers and school staff. 

Parents can work with educators to ensure that their child receives appropriate adjustments, such as extra time on tests, access to audiobooks or modified assignments, all of which can be tailored to their child’s neurological profile.

The British Dyslexia Association are a membership organisation working to achieve a dyslexia-friendly society for all. They offer resources for understanding dyslexia and finding diagnostic assessments. They also provide a directory of assessors.

Dyslexia Action provides diagnostic assessments and support services across the UK.

Schools can often refer students to an educational psychologist for a formal assessment.

Conclusion

By exploring the brain’s structure, function and processing mechanisms, we gain valuable insights into why individuals with dyslexia experience challenges with reading and language. This deeper comprehension not only dispels common myths but also underscores the importance of tailored educational strategies and early interventions. As research continues to advance, our ability to support those with dyslexia will only improve, paving the way for more inclusive and effective approaches to learning. 

If you are dyslexic The Dyslexia Association provides a wide range of services to directly assist and improve the lives of dyslexics of any age.