Dyslexia: Theories and brain-based interventions

Dyslexia, a neurodevelopmental disorder affecting 7–15% of individuals, is marked by persistent difficulties in reading that cannot be attributed to sensory or cognitive deficits, motivation, or inadequate instruction. This disorder is prevalent across various languages and manifests as impairments in reading, spelling, and comprehension due to challenges in phonological processing. Key theories explaining dyslexia include the phonological theory, which attributes it to deficits in phonological awareness, short-term verbal memory, and lexical retrieval, and the temporal processing theory, which links it to difficulties in processing rapidly presented stimuli. Another theory, the cerebellar theory, posits that dyslexia arises from cerebellar dysfunction, impacting motor control and cognitive efficiency. The magnocellular pathway theory suggests that dyslexia involves deficits in the visual system’s ability to process rapid movements and spatial location. Visual attention deficits, affecting the ability to prioritize and analyze sensory input, are also implicated. Brain imaging studies reveal reduced activation in dyslexic individuals in areas critical for reading, such as the left dorsal temporo-parietal and ventral occipito-temporal regions. These findings support the involvement of the magnocellular pathway in reading difficulties. Interventions have evolved from practice-based methods to brain-based approaches. Transcranial direct current stimulation (tDCS) has shown promise in improving reading fluency and comprehension by enhancing cortical excitability. Studies indicate that tDCS, particularly when targeting the V5 area and left parieto-temporal regions, can significantly improve reading skills in dyslexic individuals. Future research is needed to explore the effects of tDCS on the magnocellular pathway and its potential to enhance reading comprehension further.