Language lateralization was assessed by two independent functional techniques, fMRI and a dichotic listening test (DLT), in an attempt to establish a reliable and non-invasive protocol of dominance determination. This should particularly address the high intraindividual variability of language lateralization and allow decisionmaking in individual cases. Functional MRI of word classification tasks showed robust language lateralization in 17 right-handers and 17 left-handers in terms of activation in the inferior frontal gyrus. The DLT was introduced as a complementary tool to MR mapping for language dominance assessment, providing information on perceptual language processing located in superior temporal cortices. The overall agreement of lateralization assessment between the two techniques was 97.1%. Conflicting results were found in one subject, and diverging indices in ten further subjects. Increasing age, non-familial sinistrality, and a non-dominant writing hand were identified as the main factors explaining the observed mismatch between the two techniques. This finding stresses the concept of an intrahemispheric distribution of language function that is obviously associated with certain behavioral characteristics.

We investigated the influence of different task demands, task designs, and presentation modalities on the functional MRI activation patterns during a language lateralization task in a group of 14 right-handed control subjects. A word classification task was presented as target task appropriate to evoke language-related activation in the inferior frontal gyrus (IFG) Index terms: language dominance; laterality index; fMRI performance; stimulus modality; task design Abbreviations: EHI ϭ Edinburgh handedness inventory, fMRI ϭ functional MRI, IFG ϭ inferior frontal gyrus, IAP ϭ intracarotid amobarbital procedure NONINVASIVE DETERMINATION OF LANGUAGE DOMINANCE and functional localization of languagerelated cortices have become an important clinical application of functional MRI (fMRI). They demand high reliability and reproduceability of dominance assessment and the control of external and internal factors that may influence activation patterns and thereby account for an intra-and interindividual variability. Several comparative studies have already shown a reasonable agreement between the fMRI technique and the present gold standard, the intracarotid amobarbital procedure (IAP) (1-4). Nevertheless, the wide usage of fMRI in the clinical setting has to meet high standards and demands in the best case a valid scanning protocol applicable in all laboratories..FMRI-based functional lateralization is purely based on activated pixels in language-related cortices evoked by various word classification and speech production tasks. To isolate the relevant cognitive process, the MR design demands a comparison of the relevant target task with an appropriate baseline condition. Even slight changes of this design may significantly influence the outcome, i.e., the lateralization index, which then contributes to an intraindividual variability of data. Thereby, functional decision-making may be complicated and in some cases ambiguous. The present study sought to investigate the influence of certain cofactors on the functional data.Previous fMRI research has applied various paradigms to assess the dominant eloquent side of the brain, mainly based on activations of the fronto-opercular cortices. Word and sentence production tasks (5) have been applied, as well as word classification tasks (1,3,4). The activation in the inferior prefrontal gyrus (BA 45, 46, and 47) during lexical and semantic encoding in word classification tasks has been claimed to define global hemispheric dominance of speech. In our scanning protocol we investigate the influence of different target and control tasks on the functional outcome and suggest an appropriate task design for lateralization assessment in the IFG.Moreover, we address the questions of whether and how task performance is affecting the functional outcome. The influence of behavioral data on the resulting activations is still under debate. However, such knowledge is essential, as the clinical applications of fMRI mainly deal with neurologically and psychologically impaired patients. Price and Fris...

A 48-year-old patient who had aphasia due to a left subcortical hemorrhage underwent three follow-up examinations to assess MR signal changes accompanying recovery. A word classification task was applied. During the 6-month follow-up period, we observed a dynamic change from negative toward positive blood oxygenation level-dependent MR signals, i.e., task-related reafferentation of eloquent cortices occurred. Clinical improvement from aphasia paralleled the MR signal changes.

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