In a breakthrough study by researchers at the Georgetown University Medical Center and published in The Journal of Neuroscience, scientists have localized distinct cortical contributions to reading processes in left hemisphere stroke survivors, offering fresh insights into the neurobiological underpinnings of reading. This pioneering research, conducted by Dickens J. Vivian, Mackenzie E. Fama, Andrew T. DeMarco, Elizabeth H. Lacey, Rhonda B. Friedman, and Peter E. Turkeltaub, was supported by the National Institutes of Health (NIH) and its results were published under DOI:10.1523/JNEUROSCI.2707-18.2019.
The Study
The study involved 73 left hemisphere stroke survivors, both male and female, who had not been preselected for stereotyped reading dissociations. Using support vector regression lesion-symptom mapping (LSM), the researchers assessed the impact of lexicality, orthographic regularity, and concreteness on reading abilities. The terms ‘lexicality’, ‘orthographic regularity’, and ‘concreteness’ refer to words versus pseudowords, regular versus irregular spelling-sound correspondences, and concrete versus abstract meaning, respectively. Their findings not only confirm existing theories about reading processes being reliant on language-general circuitry but also bring forth new information on specific cortical regions’ roles in reading pseudowords, regular words, and concrete words.
Major Findings
Key cortical regions were identified for their contribution to different aspects of the reading process:
Reading pseudowords (words that don’t exist but follow phonetic rules) depends on the ventral precentral gyrus.
Decoding regular words (words with consistent spelling-sound correspondences) involves regions including the planum temporale, supramarginal gyrus, ventral precentral and postcentral gyrus, and the insula.
Processing concrete words (words that denote tangible objects or concepts) engages brain areas such as pars orbitalis and pars triangularis.
These findings highlight how specific brain regions are associated with different elements of reading. The ventral precentral gyrus, for instance, appears crucial for phonological decoding, which aligns with its role in integrating sound and motor processes.
Implications for Neuroscience and Education
The implications of this study extend into several realms, notably neuroscience, clinical neurology, and education. In stroke survivors who develop alexia (reading difficulties), the identification of the underlying neural mechanisms is fundamental for the development of effective rehabilitation strategies. Furthermore, understanding the neurobiological foundation of reading can inform educational approaches and interventions designed to assist with reading difficulties in the general population.
Future Directions
While this study represents a significant milestone, it also paves the way for further exploration. Future research might consider:
Extending the analysis to a broader demographic, including individuals with developmental reading disorders.
Investigating the variance in the neurobiological basis of reading across different languages with varying orthographic depths.
Examining the interaction between phonological and lexical-semantic processes in real-time using functional imaging techniques.
Keywords
1. Neurobiology of Reading
2. Cortical Contributions to Reading
3. Phonetic Decoding in the Brain
4. Reading Difficulties and Stroke
5. Lexical-Semantic Brain Processes
References
1. Dickens, J., Fama, M. E., DeMarco, A. T., Lacey, E. H., Friedman, R. B., & Turkeltaub, P. E. (2020). Localization of Phonological and Semantic Contributions to Reading. The Journal of Neuroscience, 39(27), 5361-5368. doi: 10.1523/JNEUROSCI.2707-18.2019
2. Jobard, G., Crivello, F., & Tzourio-Mazoyer, N. (2003). Evaluation of the dual route theory of reading: a meta-analysis of 35 neuroimaging studies. NeuroImage, 20, 693-712.
3. Binder, J. R., Desai, R. H., Graves, W. W., & Conant, L. L. (2009). Where is the semantic system? A critical review and meta-analysis of 120 functional neuroimaging studies. Cereb Cortex, 19, 2767–2796.
4. Turkeltaub, P. E., & Coslett, H. B. (2010). Localization of sublexical speech perception components. Brain and Language, 114(1), 1–15.
5. Vinckier, F., Dehaene, S., Jobert, A., Dubus, J. P., Sigman, M., & Cohen, L. (2007). Hierarchical coding of letter strings in the ventral stream: dissecting the inner organization of the visual word-form system. Neuron, 55(1), 143–156.
With the scientific community’s increasing interest in the cognitive and neural mechanisms of language and reading, this study provides critical contributions that have the potential to influence a variety of academic and clinical practices. This milestone paves the path for a more nuanced understanding of the neurobiology behind one of humanity’s most complex and fundamental skills – reading.