Exploring cerebral laterality of writing and the relationship to handedness: a functional transcranial Doppler ultrasound investigation

ABSTRACT

Cerebral lateralization of oral language has been investigated in a plethora of studies and it is well established that the left hemisphere is dominant for production tasks in the majority of individuals. However, few studies have focused on written language and even fewer have sampled left-handers. Writing comprises language and motor components, both of which contribute to cerebral activation, yet previous research has not disentangled. The aim of this study was to disentangle the language and motor components of writing lateralization. This was achieved through the comparison of cerebral activation during (i) written word generation and (ii) letter copying, as assessed by functional Transcranial Doppler (fTCD) ultrasound. We further assessed cerebral laterality of oral language. The sample was balanced for handedness. We preregistered the hypotheses that (i) cerebral lateralization of the linguistic component of writing would be weaker in left-handers compared to right-handers and (ii) oral language and the linguistic component of written language would not be correlated in terms of cerebral lateralization. No compelling evidence for either of our hypotheses was found. Findings highlight the complexity of the processes subserving written and oral language as well as the methodological challenges to isolate the linguistic component of writing.

KEYWORDS:

• Cerebral lateralization
• writing
• functional transcranial Doppler ultrasound
• handedness

Acknowledgements

We would like to thank all the people who showed interest and participated or helped recruit participants for this study. More specifically, we appreciate the help of Chionia Manola and Panagiotis Sampanis in recruiting participants and collecting data.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Ethical considerations

The study has received ethical approval from the National and Kapodistrian University, School of Education (Protocol Number: 1936/02.25.2020) and the Biomedical Research Foundation of the Academy of Athens’ Ethics Committee (Protocol Number: 66/05.25.2020). The data collection started no sooner than the acceptance of Stage 1 submission and we registered to resubmit Stage 2 manuscript within 5 months.

Data availability statement

All materials, code and data have been uploaded in the Open Science Framework online repository (https://osf.io/56vnq/).

Additional information

Funding

This work is funded by the Hellenic Foundation for Research and Innovation (H.F.R.I.) under the “1st Call for H.F.R.I. Research Projects to support Faculty members and Researchers and the procurement of high value research equipment grant” [grant number HFRI-FM17-746]. Authors declare no conflicts of interest.