The influence of the laboratory environment on the measurement of language lateralisation

Hemispheric lateralisation can be assessed with both functional magnetic resonance imaging (fMRI) and functional transcranial Doppler ultrasonography (fTCD). However, concordance between these techniques is imperfect. This discrepancy may be partially explained by differences in the fMRI and fTCD laboratory environments: while fMRI occurs in a noisy, confined space in which subjects lie supine, fTCD typically occurs in a quiet, unconfined space in which subjects sit upright. This study investigated the influence of the fMRI and fTCD laboratory environments on the measurement of language lateralisation. Across two experiments, fTCD was used to measure the consistency of language lateralisation while participants performed a word generation task either twice in an fTCD environment (control condition), or once in an fTCD environment and then in a simulated fMRI environment (experimental condition). Relative to the control condition, test-retest reliability of lateralisation estimates was considerably poorer in the experimental condition. Consistent with this, several participants in the experimental condition switched lateralisation categories between the two testing sessions. These findings suggest that the laboratory environment may partially account for the discordance between fMRI and fTCD lateralisation estimates. Future research should embrace protocols that aim to reduce the interference of the laboratory environment, such as noise-cancelling headphones and open, multi-postural fMRI, to further our understanding of hemispheric lateralisation.