Predictive coding in subcortical sensory pathways and developmental dyslexia

• Applicant: Professorin Dr. Katharina von Kriegstein
• Subject Area: Biological Psychology and Cognitive Neuroscience ; Cognitive, Systems and Behavioural Neurobiology
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 522859374

Developmental dyslexia is a learning disorder with a high prevalence (5-15%). It is characterised by reading and/or writing difficulties that persist into adulthood and that can interfere with educational and vocational success. The neurological processes that lead to dyslexia are hotly debated. Most neuroscientific research on dyslexia focuses on the cerebral cortex, and there is solid evidence that dyslexia is associated with cortex alterations. There are, however, also indications that dyslexia is associated with alterations in subcortical sensory pathways, particularly in the left auditory and visual thalami (medial geniculate body, MGB; lateral geniculate body, LGN) and their connections to the cerebral cortex. The left-hemispheric thalamo-cortical alterations are related to a key dyslexia diagnostic score: the ability to rapidly name letters and numbers (RANln). One potential mechanistic explanation of thalamo-cortical alterations in dyslexia is a deficit with predictive coding. The predictive coding framework is one of the most promising neuroscientific theories of perceptual processing to-date. It postulates that the brain constantly maintains and updates an internal model of the sensory world by testing its predictions (or priors) against the sensory input. Although the predictive coding framework has been developed for the cerebral cortex, recent findings in typically reading individuals revealed that also the MGB processes sounds according to mechanisms postulated by predictive coding. Whether the predictive coding mechanism in the MGB is altered in dyslexia is to-date unclear. In addition, it is unknown whether a similar predictive coding mechanism as in the MGB is also used in the visual modality, in the LGN. Our overarching aim is to directly test whether there are alterations in predictive coding mechanisms in the sensory thalamus (left MGB and LGN) in dyslexia. Here, we plan two experiments using high-resolution functional magnetic resonance imaging (fMRI) in groups of adult dyslexics and typically reading controls. In the first experiment, we plan to test the hypotheses that dyslexia is associated with a reduced amount of predictive coding specifically in the left MGB and that these potential alterations in the left MGB in dyslexia are related to RANln performance. In the second experiment, we test - in typically reading adults - the hypothesis that responses in the LGN can be explained by predictive coding mechanisms. If successful, this experiment will be a basis for future investigations into the mechanisms of potential LGN dysfunction in dyslexia. We expect that the results will provide a mechanistic explanation of sensory thalamus alterations in dyslexia and help to resolve opposing predictions of current theories on dyslexia. In addition, the second experiment will provide a fundamental step for the mechanistic bases for visual processing in the human visual thalamus in typically reading adults.

• DFG Programme: Research Grants
• International Connection: United Kingdom
• Cooperation Partner: Dr. Alejandro Tabas