Neuroanatomy and neurobiology of dyslexia

Dyslexia, a learning disorder that affects the acquisition and development of reading skills, has its roots in the complexity of the neuroanatomy and neurobiology of the human brain.

In this session, we will explore in detail how dyslexia is linked to the organization and functioning of the brain, analyzing everything from specific brain areas to neuronal processes and the research that has shed light on this condition.

The Importance of Neuroanatomy in Understanding Dyslexia

• The Cerebral Cortex and its Role in Dyslexia: The cerebral cortex, the outermost layer of the brain, is crucial to understanding dyslexia. Various cortical regions are involved in reading, including the fusiform gyrus, the angular gyrus and the inferior frontal gyrus. Understanding the specific function of these areas is essential to elucidate the neuroanatomical basis of dyslexia. Importance of Connectivity Between Regions: The connectivity between these regions is equally relevant. The corpus callosum, a structure that connects the cerebral hemispheres, and the neural pathways that link specialized cortical areas play an essential role in the coordination necessary for reading. Anomalies in connectivity may contribute to the challenges experienced by those with dyslexia.

Fusiform Gyrus and Visual Word Processing

• Function of the Fusiform Gyrus: The fusiform gyrus, located in the temporal lobe, is fundamental for visual word processing. This region specializes in the recognition of complex visual patterns, including the shape of written letters and words. Abnormalities in the fusiform gyrus have been identified in individuals with dyslexia, contributing to difficulties in visual decoding.

• Brain Imaging Research: Brain imaging studies, such as functional magnetic resonance imaging (fMRI), have revealed that the fusiform gyrus may show atypical or decreased activation in individuals with dyslexia during reading tasks. This evidence supports the hypothesis that differences in visual processing are a central feature of dyslexia.

Angular Gyrus and Phonological Processing

• Role of the Angular Gyrus in Phonology: The angular gyrus, located in the parietal lobe, plays a crucial role in phonological processing during reading. This region converts the visual symbols of letters into sounds, enabling the pronunciation of words. Difficulties in angular gyrus are linked to difficulties in associating letters with sounds, a common feature in dyslexia.

• Challenges in Grapheme-Phoneme Conversion: Neurobiological research has revealed that angular gyrus may show altered activation in individuals with dyslexia during phonological processing tasks. Difficulties in grapheme-phoneme conversion, essential for reading, are associated with abnormalities in this region.

Inferior Frontal Gyrus and Lexical Processing

• Role of the Inferior Frontal Gyrus: The inferior frontal gyrus, located in the frontal lobe, is associated with lexical processing during reading. This region is essential for accessing the mental lexicon, which stores words and their meanings. Difficulties in the inferior frontal gyrus can affect the recognition of familiar words and lexical comprehension. Connections with the Memory and Attention System: In addition, the inferior frontal gyrus is connected to regions associated with working memory and attention functions. The ability to access information stored in memory and to maintain attention during reading is fundamental for the efficient processing and comprehension of text.

Neuronal Plasticity and the Development of Dyslexia

• Neuronal Plasticity in Childhood: During childhood, the brain exhibits remarkable neuronal plasticity, and the development of dyslexia may be linked to alterations in this plasticity. The brain's ability to adapt and reorganize itself in response to new experiences, such as learning to read, can influence the presence and severity of dyslexia.

• Genetics and Environmental Factors: Research suggests that both genetic and environmental factors may contribute to the development of dyslexia. Twin studies have revealed a genetic predisposition, but interaction with environmental factors, such as the quality of education, also plays a significant role.

Challenges in Brain Connectivity and Dyslexia

• Corpus Callosum and Hemispheric Coordination: The corpus callosum, the structure that facilitates communication between the cerebral hemispheres, plays an essential role in reading. Anomalies in this connection can affect the hemispheric coordination necessary for the efficient integration of visual and phonological information during reading. Functional disconnections: Neurobiological studies have revealed functional disconnections between key regions of the brain in individuals with dyslexia. Lack of synchronization between specialized areas can affect fluidity and precision in the processing of information during reading.

Advanced Research in the Neurobiology of Dyslexia

• Developments in Brain Imaging: Advances in brain imaging technology, such as magnetoencephalography (MEG) and diffusion tensor imaging (DTI), have enabled more precise investigations into neuronal activity and connections in the brains of people with dyslexia. These tools provide a more detailed understanding of the brain dysfunctions associated with dyslexia.

• Molecular Genetics: Research in molecular genetics is unraveling the specific genetic components associated with dyslexia. The identification of genetic variants may offer new avenues for understanding the underlying causes and developing more specific therapeutic approaches.