Does writing handedness affect neural representation of symbolic number? An fMRI adaptation study

A key question in the field of numerical cognition is how the human brain represents numerical symbols (e.g., Arabic digits). A large body of research has implicated left parietal regions in symbolic number processing. One possible explanation for this lateralization of neural activity is the handedness of participants. Specifically, participants in neuroimaging research are almost exclusively right-handed. The current study sought to probe whether number representation in the brain is associated with hand preference for handwriting. To address this question, we used functional Magnetic Resonance Imaging (fMRI) to compare brain activation of a group of right-handed participants with a group of left-handed participants during the passive viewing of symbolic numbers. At the whole-brain level, the right-handers demonstrated a previously obtained left-lateralized effect within the intraparietal sulcus (IPS). The left-handers showed some evidence of reverse lateralization of this effect in the IPS. However, when the groups were statistically compared, we found no regions that demonstrated group-level differences. In a follow-up region of interest (ROI) analysis within the left and right parietal lobes, we calculated laterality indices for each participant. Results did not provide support for group differences in laterality within the right or left IPS ROI. These findings do not support the hypothesis that handwriting plays a role in the lateralization of symbolic number processing in the brain. Further research is needed to better understand the factors that lead to left-lateralization for symbolic number processing.