Functional MR Imaging of Working Memory in the Human Brain

OBJECTIVE: In order to investigate the functional brain anatomy associated with verbal and visual working memory, functional magnetic resonance imaging was performed. MATERIALS AND METHODS: In ten normal right handed subjects, functional MR images were obtained using a 1.5-T MR scanner and the EPI BOLD technique. An item recognition task was used for stimulation, and during the activation period of the verbal working memory task, consonant letters were used. During the activation period of the visual working memory task, symbols or diagrams were employed instead of letters. For the post-processing of images, the SPM program was used, with the threshold of significance set at p < .001. We assessed activated brain areas during the two stimulation tasks and compared the activated regions between the two tasks. RESULTS: The prefrontal cortex and secondary visual cortex were activated bilaterally by both verbal and visual working memory tasks, and the patterns of activated signals were similar in both tasks. The superior parietal cortex was also activated by both tasks, with lateralization to the left in the verbal task, and bilaterally without lateralization in the visual task. The inferior frontal cortex, inferior parietal cortex and temporal gyrus were activated exclusively by the verbal working memory task, predominantly in the left hemisphere. CONCLUSION: The prefrontal cortex is activated by two stimulation tasks, and this is related to the function of the central executive. The language areas activated by the verbal working memory task may be a function of the phonological loop. Bilateral prefrontal and superior parietal cortices activated by the visual working memory task may be related to the visual maintenance of objects, representing visual working memory.

Determination of Dominant Hemishere for Language: Comparison of fMRI and Wada Test

PURPOSE: To evaluate the usefulness of functional MR imaging(fMRI) for determination of language dominance compared with Wada test and to assess the lateralization of activated signals according to stimulation task of activated area. MATERIALS AND METHODS: Functional maps were obtained during word generation task and reading task in twenty patients(16 epilepsy, 4tumor; 17 right-handed, 1 left-handed, 2 ambidextrous). MR examinations were performed at 1.5T scanner with EPI BOLD technique during word generation and word reading tasks. We used SPM program for the postprocessing of image. The threshold for significance was set at p<0.0001 or p<0.001. A lateralization index(LI) was calculated from the number of activated pixels in three hemispheric areas(whole hemisphere, frontal lobe, and temporoparietal lobe. The LIs of fMRI and Wada test were compared according to stimulation task and area for calculation of LI. RESULTS: During the Wada test, sixteen patients had the left language dominance and four patients had right dominance. The language dominance determined by LI of fMRI in each hemisphere was concordant with the result of Wada in 19(95%) by word generation task and in 15(75%) by reading task. At word generation task, the concordance rate was higher with LI calculated on whole hemisphere than that on frontal(80%) or temporoparietal lobe(90%). Correlation between the LIs of Wada and fMRI was significant(r=0.74) CONCLUSION: In fMRI word generation task produced stronger activation of language areas and showed more accurate lateralization reading task. The concordance rate of and Wada test was higher with LI calculated on whole hemisphere than on frontal or temporoparietal lobe.

A Functional MR Imaging Study of Reading

PURPOSE: To evaluate the language areas activated by fMRI during different reading tasks and to assess the difference of activated areas according to each reading task MATERIALS AND METHODS: Functional maps of the language area were obtained during three reading tasks(Korean consonant letter, pseudoword, and word) in nine right-handed volunteers(7 males, 2 females). MR examinations were performed at 1.5T scanner with EPI BOLD technique(gradient echo shot EPI, TR/TE 3000/60, flip angle 90, matrix64 64, 5mm thickness, no slice gap). Each task consisted of three resting periods and two activation periods and each period lasted 30 seconds. We used SPM program for the postprocessing of images and siginficance level was set at p<0.01. Activated areas were topographically analyzed in each stimulus. RESULTS: Significant activated signals were demonstrated in all volunteers. Activated signals were seen in the frontal, temporal, parietal and occipital lobes during reading tasks and they were lateralized to the left hemisphere except occipital lobe. Letter and pseudoword produced stronger activated signals than word, and the activated signals were more lateralized to the left hemisphere in pseudoword reading than in letter reading. CONCLUSION: Activated signals were induced in the language areas by reading task of letter or wordform. Greater activation of language areas was induced when letter or pseuowords were presented than familiar words.