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The Acquisition, Analyses and Interpretation of fMRI Data: A Study on Functional Specialisation in Primary Auditory Cortices

Vol. 3 No. 2, 2008

Original article

Author

Yusoff AN, Abdul Hamid K, Mohamad M, Abd Hamid AI

Abstrak

Dalam kajian ini, pengimejan resonans magnet kefungsian (fMRI) digunakan untuk mengkaji pengkhususan kefungsian dalam korteks auditori manusia semasa mendengar. Paradigma fMRI senyap digunakan untuk mengurangkan artifak bunyi pengimbas di atas imej kefungsian. Subjek dikehendaki menumpukan perhatian kepada stimulus hingar putih yang diperdengarkan secara binaural pada keamatan 70 dB lebih tinggi daripada aras pendengaran manusia normal. Pengkhususan kefungsian dikaji menggunakan perisian Pemetaan Statistik Berparameter (SPM5) yang berasaskan Matlab melalui analisis kesan malar (FFX), kesan rawak (RFX) dan konjunksi. Analisis individu ke atas semua subjek menunjukkan pengaktifan bilateral yang tidak simetri di antara hemisfera kanan dan kiri pada kawasan Brodmann (BA) 22, 41 dan 42, melibatkan korteks auditori primer dan sekunder. Peratus perubahan isyarat didapati lebih besar di ketiga-tiga BA22, 41 dan 42 kanan berbanding dengan yang di sebelah kiri (p>0.05). Purata bilangan voksel aktif bagi kesemua kawasan Brodmann tersebut juga didapati lebih tinggi di hemisfera kanan berbanding dengan kiri (p>0.05). Keputusan FFX menunjukkan titik pengaktifan maksimum berlaku pada BA41 kanan dengan sebanyak 599±1 voksel aktif dicerap di lobus temporal kanan berbanding 485±1 di lobus temporal kiri. Keputusan FFX didapati tekal dengan keputusan purata bagi kesemua subjek. Analisis konjunksi kemudiannya menunjukkan BA41 kanan dan BA22 kiri sebagai kawasan pengaktifan sepunya dalam kesemua subjek. Keputusan yang diperolehi mengesahkan pengkhususan korteks auditori kanan dalam pemprosesan stimulus bukan pertuturan.

Kata kunci

Analisis kesan malar (FFX), Analisis kesan rawak (RFX), Analisis kon-junksi, Kawasan Brodmann (BA), Pemetaan Statistik Berparameter (SPM), Pengimejan Resonans Magnet Kefungsian (fMRI)

Abstract

In this study, functional magnetic resonance imaging (fMRI) is used to investigate functional specialisation in human auditory cortices during listening. A silent fMRI paradigm was used to reduce the scanner sound artefacts on functional images. The subject was instructed to pay attention to the white noise stimulus binaurally given at an intensity level of 70 dB higher than the hearing level for normal people. Functional specialisation was studied using the Matlab-based Statistical Parametric Mapping (SPM5) software by means of fixed effects (FFX), random effects (RFX) and conjunction analyses. Individual analyses on all subjects indicated asymmetrical bilateral activation of the left and right hemispheres in Brodmann areas (BA) 22, 41 and 42, involving the primary and secondary auditory cortices. The percentage of signal change is larger in the BA22, 41 and 42 on the right as compared to the ones on the left (p>0.05). The average number of activated voxels in all the respective Brodmann areas are higher in the right hemisphere than in the left (p>0.05). FFX results showed that the point of maximum intensity was in the right BA41 whereby 599±1 activated voxels were observed in the right temporal lobe as compared to 485±1 in the left temporal lobe. The RFX results were consistent with that of FFX. The analysis of conjunction which followed, showed that the right BA41 and left BA22 as the common activated areas in all subjects. The results confirmed the specialisation of the right auditory cortices in processing non verbal stimuli.