Cerebral laterality of writing in right- and left- handers: A functional transcranial Doppler ultrasound study

The cerebral lateralization of written language has received very limited research attention in comparison to the wealth of studies on the cerebral lateralization of oral language. The purpose of the present study was to further our understanding of written language lateralization, by elucidating the relative contribution of language and motor functions. We compared written word generation with a task that has equivalent visuomotor demands but does not include language: the repeated drawing of symbols. We assessed cerebral laterality using functional transcranial Doppler ultrasound (fTCD), a non-invasive, perfusion-sensitive neuroimaging technique in 23 left- and 31 right-handed participants. Findings suggest that the linguistic aspect of written word generation recruited more left-hemispheric areas during writing, in right-handers compared to left-handers. This difference could be explained by greater variability in cerebral laterality patterns within left-handers or the possibility that the areas subserving language in left-handers are broader than in right-handers. Another explanation is that the attentional demands of the more novel symbol copying task (compared to writing) contributed more right-hemispheric activation in right-handers, but this could not be captured in left-handers due to ceiling effects. Future work could investigate such attentional demands using both simple and complex stimuli in the copying condition.

Cerebral Lateralization During Handwritten and Typed Word Generation: A Functional Transcranial Doppler Ultrasound Study in Left-Handers and Right-Handers

Cerebral lateralization of written language, much like oral language, is predominantly left lateralized. However, handwriting has been the primary focus in lateralization studies. The cerebral lateralization of typing-a widely used method of writing-remains unexamined. This preregistered study aimed to explore the cerebral lateralization of typing versus handwriting and to investigate possible handedness-related differences. We hypothesized that (i) cerebral lateralization would not differ between the two writing methods after movement correction and (ii) both handwriting and typing would show weaker lateralization in left-handers compared to right-handers. To investigate this, we used functional transcranial Doppler (fTCD) ultrasound, a reliable method for assessing cerebral lateralization during language tasks that remains unaffected by movement artifacts, such as those generated by handwriting and typing. A total of 24 left-handers and 30 right-handers participated, performing written word generation through both handwriting and typing on a computer keyboard while undergoing fTCD assessment. We applied a Bayesian framework for our analysis, as it enables us to demonstrate the absence of a difference (i.e., no difference between two variables), which is not possible with the use of p values (estimated under the frequentist framework). Our results provided evidence supporting the absence of a difference in cerebral lateralization between handwriting and typing after movement correction. However, we found no conclusive evidence to either support or refute a difference in lateralization between left-handers and right-handers, suggesting that more research is needed to clarify the role of handedness in cerebral lateralization for different writing methods.