Functional MRI Assessment of Hemispheric Language Dominance with Using a Lexical Decision Task

Ryoo, Jae Wook; Choi, Dae Seob; Na, Dong Gyu; Cho, Jae Min; Kim, Sam Soo; Park, Euidong; You, Jin Jong; Cha, Sang Hoon

Abstract

PURPOSE: We wanted to compare the fMRIs (functional magnetic resonance images) obtained during a lexical decision task and also during a word generation task, and we wanted to evaluate the usefulness of using a lexical decision task for the visualization of the brain language area and for the determination of language dominance.
MATERIALS AND METHODS
Sixteen patients (9 women and 7 men) who had had undergone the Wada test were included in our study. All the patients were left dominant for language, as tested for on the Wada test. The functional maps of the brain language area were obtained in all the subjects during the performance of a lexical decision task and also during the performance of a word generation task. The MR examinations were performed with a 1.5 T scanner and with using the EPI BOLD technique. We used the SPM program for the postprocessing of the images. The threshold for significance was set at p<0.001 or p<0.01. A lateralization index was calculated from the number of activated pixels in each hemispheric region (the whole hemisphere, the frontal lobe and the temporoparietal lobe), and the hemispheric language dominance was assessed by the lateralization index; the results were then compared with those results of the Wada tests. The differences for the lateralization of the language area were analyzed with regard to the stimulation tasks and the regions used for the calculation of the lateralization indices.
RESULTS
The number of activated pixels during the lexical decision task was significantly smaller than that of the word generation task. The language dominance based on the activated signals in each hemisphere, was consistent with the results of the Wada test for the word generation tasks in all the subjects. On the lexical decision task, the language dominance, as determined by the activated signals in each hemisphere and the temporoparietal lobe, correlated for 94% of the patients. The mean values of the lateralization index for the lexical decision task were higher than those mean values of the lateralization index of the word generation task.
CONCLUSION
The lexical decision task allowed us to map the language area and to determine the language dominance. It could be a useful task for those patients who cannot perform the word generation task because of their cognitive retardation.