Functional MRI of the Language System. In: Moonen C, Bandettini PA, editors. Functional MRI. Berlin: Springer Berlin Heidelberg; 2000. pp. 407-19. [DOI: 10.1007/978-3-642-58716-0_33]

Assessment of the language laterality index in patients with brain tumor using functional MR imaging: effects of thresholding, task selection, and prior surgery

BACKGROUND AND PURPOSE

Functional MR imaging (fMRI) is used to determine preoperatively the laterality of cortical language representation along with the relationship of language areas to adjacent brain tumors. The purpose of this study was to determine whether changing the statistical threshold for different language tasks influences the language laterality index (LI) for a group of controls, patients with tumor without prior surgery, and patients with tumor and prior surgery.

MATERIALS AND METHODS

Seven controls, 9 patients with tumor without prior surgery, and 4 patients with tumor and prior surgery performed verb-generation, phonemic fluency, and semantic fluency language tasks during fMRI. Interhemispheric activation differences between the left and right Broca regions of interest were determined by calculating language LIs. LIs were compared within each group, between groups, and between language tasks. Intraoperative electrocortical mapping or the presence of aphasia during postoperative neurology examinations or both were used as ground truth.

RESULTS

The language LI varied as a result of statistical thresholding, presence of tumor, prior surgery, and language task. Although patients and controls followed a similar shape in the LI curve, there was no optimal P value for determining the LI. Three patients demonstrated a shift in the LI between hemispheres as a function of statistical threshold. Verb generation was the least variable task both between tasks and across groups.

CONCLUSION

For preoperative patients with tumor, the LI should be examined across a spectrum of P values and a range of tasks to ensure reliability. Our data suggest that the LI may be threshold- and task-dependent, particularly in the presence of adjacent tumor.

Global and local development of gray and white matter volume in normal children and adolescents

Over the last decade, non-invasive, high-resolution magnetic resonance imaging has allowed investigating normal brain development. However, much is still not known in this context, especially with regard to regional differences in brain morphology between genders. We conducted a large-scale study utilizing fully automated analysis-approaches, using high-resolution MR-imaging data from 200 normal children and aimed at providing reference data for future neuroimaging studies. Global and local aspects of normal development of gray and white matter volume were investigated as a function of age and gender while covarying for known nuisance variables. Global developmental patterns were apparent in both gray and white matter, with gray matter decreasing and white matter increasing significantly with age. Gray matter loss was most pronounced in the parietal lobes and least in the cingulate and in posterior temporal regions. White matter volume gains with age were almost uniform, with an accentuation of the pyramidal tract. Gender influences were detectable for both gray and white matter. Voxel-based analyses confirmed significant differences in brain morphology between genders, like a larger amygdala in boys or a larger caudate in girls. We could demonstrate profound influences of both age and gender on normal brain morphology, confirming and extending earlier studies. The knowledge of such influence allows for the consideration of age- and gender-effects in future pediatric neuroimaging studies and advances our understanding of normal and abnormal brain development.

Temporal Dissociation of Early Lexical Access and Articulation Using a Delayed Naming Task — An fMRI Study

Neuroimaging studies of overt speech hold an important practical advantage allowing monitoring of subject performance, particularly valuable in disorders like aphasia. However, speech production is not a monotonic process but a complex sequence of stages. Levelt and colleagues have described these as roughly corresponding to two originally independent systems--conceptual and sensorimotor--that are linked in the formulation and expression of spoken language. In the initial stages a word is chosen to match a concept (lexical selection); in the later stages the sound and motor patterns are encoded and the word is uttered (articulation). It has been difficult to discriminate these stages using conventional neuroimaging techniques. We designed a functional magnetic resonance imaging study in an attempt to do this, by introducing a latency into a conventional naming paradigm, delaying the articulated response. Our results showed that left hemisphere perisylvian areas were active throughout, interacting with visual and heteromodal areas during early lexical access and with motor and auditory areas during overt articulation. These results are consistent with the broadest version of the Levelt model and with that derived from Chomsky's minimalist program in which a core language system interacts with conceptual-intentional systems and articulatory-perceptual systems during the early and late stages of lexical access respectively.

Dispersed activation in the left temporal cortex for speech-reading in congenitally deaf people

Does the lateral temporal cortex require acoustic exposure in order to become specialized for speech processing? Six hearing participants and six congenitally deaf participants, all with spoken English as their first langugage, were scanned using functional magnetic resonance imaging while performing a simple speech-reading task. Focal activation of the left lateral temporal cortex was significantly reduced in the deaf group compared with the hearing group. Activation within this region was present in individual deaf participants, but varied in location from person to person. Early acoustic experience may be required for regions within the left temporal cortex in order to develop into a coherent network with subareas devoted to specific speech analysis functions.