Variation in brain lateralization during various language tasks: a functional transcranial Doppler study

Language dominance has repeatedly been demonstrated by means of functional transcranial Doppler (fTCD) ultrasonography. However, one strongly lateralizing paradigm might be an overestimation of overall language lateralization. We hypothesized that significant differences between hemodynamic patterns could be shown by using multiple language functions (such as productive and receptive tasks). Particularly, we expected more left-hemispheric activity in frontal and productive tasks and we expected less clear left-hemispheric activity in temporal regions and receptive tasks. Thirty healthy volunteers were included in the study. The lateralization index (LI) was measured with transcranial Doppler ultrasonography for each subject during four language tasks: a cued word generation task (WF), a sentence construction task (SENT), a reading task (READ), and a semantic decision task (SEMANT). Left-hemispheric dominance was found in 90%, 80%, 73.3% and 66.7% of the subjects for respectively WF, SENT, READ and SEMANT. A repeated measures analysis of variance revealed significant differences in LIs between the different language tasks (p<.01). Our results showed that productive and syntactic tasks (WF and SENT) lateralize stronger than receptive tasks (READ and SEMANT). The use of a variety of language tasks in the determination of language lateralization therefore appears to be essential in providing a more comprehensive view of language functioning.