The current study investigated the cognitive and neural substrates that underpin writing ability. We explored similarities and differences in writing numbers and words and compared these to language and manual actions in a large group of sub-acute, stroke patients (n = 740). The behavioral data showed association and dissociation in the ability to write words and numbers. Comorbidities of writing deficits with both language and motor impairments were prevalent, with less than a handful showing deficits restricted to the writing tasks. A second analysis with a subset of patients (n = 267) explored the neural networks that mediate writing abilities. Lesion to right temporal contributed to writing words, while lesions to left postcentral contributed to writing numbers. Overlapping neural mechanisms included the bilateral prefrontal cortex, right inferior parietal, left middle occipital and the right cerebellum. With the former regions associated with error pattern typical to writing based on prior knowledge (the lexical route), while lesion to left MOG was associated with errors to the phonological (non-lexical) route. Using principle components extracted from the behavioral data, we showed that right prefrontal and right parietal contributed to the ability to use pen, while lesion to bilateral prefrontal, inferior temporal and cerebellum supported unique use of pen for writing. The behavioral and imaging data suggested that writing numbers and words primarily relied on overlapping cognitive and neural functions. Incidents of pure writing deficits, in the absence of motor or language deficits were rare. Nevertheless, the PCA and neural data suggested that writing abilities were associated with some unique neuro-cognitive functions, specifically dedicated to the use of pen and the ability to transform meaning to motor command.
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We first like to acknolwdge the contribution of the late Professor Humphreys to the current work. Humphreys was the creator of the database used in the current study he helped design and analyse the study. However, due to a sudden death, he did not contribute to the final stages of the study. This work was supported by a project of Guangzhou General Science and Technology Project of Health and Family Planning (20171A010247) awarded to HC; two Guangzhou Planned Project of Science and Technology (2012J5100039) awarded to XP and (2016201604030018) awarded to JZ; the Stroke Association (TSA 2010/2) awarded to GWH. And we would like to thank to the many stroke survivors, research nurses and technician who contributed the collection of this data.
© 2019, The Author(s).
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