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3. Functional Magnetic Resonance Imaging: A Promising Tool for Defining the Organization of Chinese Language in the Brain
- Hong Kong University Press, HKU
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3 FunctionalMagneticResonance Imaging:APromisingToolfor DefiningtheOrganizationof ChineseLanguageintheBrain PaulM.Matthews, ShiminFu,Yi-PingChenandSusanIversen A fundamental proble m i n languag e studie s i s to determin e whethe r th e written for m o f a languag e influence s th e wa y i n which informatio n i s encoded i n the brain . Stud y o f th e Chines e languag e offer s a potentiall y powerful strateg y fo r addressin g thi s question . Chines e is unique relativ e to Englis h an d othe r alphabeti c language s because , with the introductio n of Pinyin, spoken language used can be represented i n two distinct forms , one wit h a morphographi c scrip t an d th e othe r wit h a phonetic-base d language. Chinese character s conve y informatio n b y virtue o f the organizatio n of line s in space . They hav e a structur e an d thei r interpretatio n depend s on it s configuratio n relativ e t o th e loca l environment . I n contrast , th e alphabetic symbol s o f Pinyi n ar e interprete d i n term s o f th e translate d sound, i n commo n wit h othe r phoneti c languages . Thes e fundamenta l differences sugges t that the underlying brain representations during reading of the tw o language s ma y b e distinct . Functional magnetic resonance imaging (fMRI ) provide s a method fo r mapping th e organizatio n o f cognitiv e processe s i n the brai n (Matthews , Clare, 6 c Adcock, 1999 ; Ogawa , Lee , Kay, 6 c Tank, 1990) . It offer s th e advantages o f bein g a non-invasive , widely diffuse d technology . Becaus e it doe s no t emplo y radioactiv e tracer s o r pos e othe r significan t risks , subjects ca n b e studie d o n man y occasions . I n this brie f revie w chapter , we will outlin e th e principal s o f fMRI , briefl y revie w the applicatio n o f 62PAU LM.MATTHEWS,SHIMINFU ,YI-PINGCHENANDSUSANIVERSE N this technique t o languag e studies , and the n discus s a new applicatio n t o the stud y o f th e Chines e language . O Functiona l Magneti c Resonance Imaging o f the Brai n Work o f Charle s Sherringto n ove r 10 0 year s ag o demonstrate d tha t increased loca l bloo d flo w accompanie s neurona l activity . The increase d blood flow results from highe r energy utilization at the synapse with either excitatory o r inhibitor y transmissio n (Villringe r 6c Dirnagl, 1995) . Th e increase i n blood flo w deliver s more oxygen to a n activate d are a o f brai n than th e enhanced metabolis m requires . In consequence, the blood i n th e capillaries servin g th e are a an d i n th e vein s drainin g fro m i t sho w a relatively greate r oxygenate d t o deoxygenate d haemoglobi n ratio . Magnetic resonance imagin g (MRI ) relie s on detection o f signal fro m the protons o f water molecule s in the tissue. The precise amount o f signa l that comes from an y part o f the tissue depends both o n the water conten t and als o o n factor s whic h contro l wha t i s known a s the 'relaxation ' o f the protons i n water. When wate r proton s ar e placed i n an are a o f local , rapidly changin g magneti c fiel d strengths , their relaxatio n rat e (1/T 2*) i s enhanced, givin g rise to greater signa l loss by the time that i t is observe d (Thulborn, Waterton , Matthews , & Radda , 1982) . Deoxyhaemoglobin i s paramagnetic , i.e . i t bend s a magneti c fiel d towards it . Thus, water proton s tha t ar e near a blood vesse l containing a higher proportion of deoxyhaemoglobin will experience a rapidly changin g local magnetic field , whic...