FMRI Study Of Presbycusis In Speech Processing

Objective To study the brain functiongal activation under speech stimulation in presby-cusis，young adults and elderly people with normal hearing by blood oxygenation level depen-dent functional magnetic resonance imaging(BOLD-fMRI)，and to research functional reorga-nization of auditory cortex and the changes of hemispheric dominance leading by aging anddeafness．Methods18normal hearing young volunteers (youth group)，10normal hearing elderlypeople (aged group) and10presbycusis patients(presbycusis group) received BOLD-fMRIunder auditory task．Experimental tasks including monosyllabic verbal stimulating at tone of1kHZ and sound intensity to90dB±3dB(after ambient noise detector Smart Sensor AR844measurement and calibration) randomly transmited to left and righr ear．Following blockdesign，each stimulus was repeated two times．SPM5software was used to deal with theoriginal pictures in the off-line work station to get fuctional maps，volume and intensity of theactivated brain regions of interest，and calculate the laterality index．Results The three groups of subjects activated basically the same regions when receivedauditory speech stimulation，and the the superior temporal gyrus and middle temporal gyrusactivation is the most obvious regions．Select auditory cortex as region of interest．For the activation volume，while giving left ear speech stimulation，compared with the youthgroup，two elderly groups’ activation volume of the left ROI increase(P <0.05)，and the rightjust opposite(P <0.05)．However，when giving right ear stimulation，both of the two elderlygroups’ activation volume of bilateral ROI were reduced(P<0.05)．Compared with the oldergroup，either giving the left ear or right ear stimulation，the presbycusis group’s bilateral ROIactivation volume was decreased，but the difference was not statistically significant．For activate strength，while giving left ear stimulation，the activation strength of the bilateralROI between the different groups were not significantly different．When giving left earstimulation，the activation strength of bilateral ROI are stronger than the other two grougs (P<0.05)．Presbycusis group weakened slightly compared with the youth group，but thedifference was not statistically significant．To young people，regardless of left or right ear stimulation，the contralateral ROI activationvolume and intensity significantly increased compared to ipsilateral，appearing contralateralhemispheric dominance，and laterality index were-0.58(left ear stimulation) and0.37(rightear stimulation)．Compared to young people，elderly people with normal hearing andpresbycusis contralateral hemisphere conduction advantage is significantly reduced under monaural stimulation，and the laterality index were-0.24，0.28(the aged group)，-0.18，0.25(presbycusis group)．Young people receiving the left and the right ear auditory task respectively，the ratio of thetotal volume of bilateral ROI activation were1:2.06，appearing to the right ear advantage (leftbrain dominance)．While the aged and presbycusis group manifested as right ear advantagedecreased (left ear advantage enhanced)，whose the total volume ratio were1:1.51，1:1.61．Conclusion Auditory verbal tasks activated brain regions in the superior temporal gyrusand middle temporal gyrus most obvious．Aging caused these brain regions activated weakerand appeared to the trend of contralateral hemisphere conducted as well as right earadvantages weakened．So the aging and deafness brought cortical reorganization，this may beone of the reason for the decline of speech recognition．...