Localization of Broca's Area Using Functional MR Imaging: Quantitative Evaluation of Paradigms

Abstract

Objective: Functional magnetic resonance imaging (fMRI) is frequently used to localize language areas in a non-invasive manner. Various paradigms for presurgical localization of language areas have been developed, but a systematic quantitative evaluation of the efficiency of those paradigms has not been performed. In the present study, the authors analyzed different language paradigms to see which paradigm is most efficient in localizing frontal language areas.

Methods: Five men and five women with no neurological deficits participated (mean age, 24 years) in this study. All volunteers were right-handed. Each subject performed 4 tasks, including fixation (Fix), sentence reading (SR), pseudoword reading (PR), and word generation (WG). Fixation and pseudoword reading were used as contrasts. The functional area was defined as the area(s) with a t-value of more than 3.92 in fMRI with different tasks. To apply an anatomical constraint, we used a brain atlas mapping system, which is available in AFNI, to define the anatomical frontal language area. The numbers of voxels in overlapped area between anatomical and functional area were individually counted in the frontal expressive language area.

Results: Of the various combinations, the word generation task was most effective in delineating the frontal expressive language area when fixation was used as a contrast (p<0.05). The sensitivity of this test for localizing Broca's area was 81% and specificity was 70%.

Conclusion: Word generation versus fixation could effectively and reliably delineate the frontal language area. A customized effective paradigm should be analyzed in order to evaluate various language functions.

Keywords: Functional MRI; Language; Paradigm; Quantitative evaluation.

Figures

Fig. 1

Anatomical region of interest of expressive language areas. This includes most of the middle and inferior frontal gyrus (http://afni.nimh.nih.gov/afni).

Fig. 2

Voxel count in overlapped area between functional and anatomical region of interest. Box graph shows mean and standard deviation values.

Fig. 3

Probablistic map of WG-Fix in frontal language area. Probabilistic mapping was overlapped on a T1 template in the Analysis of Functional Neuroimages program. The red area (upper of scale bar) represents strong activation area. Frontal activation area (red area) was well correlated with Brodmann's areas 44, 45, 47.