Sains Malaysiana 40(6)(2011): 665–678

Pemerolehan, Analisis dan Interpretasi Data fMRI: Kehubungan Efektif dalam Korteks Auditori Primer Manusia

(Acquisition, Analyses and Interpretation of fMRI Data: A Study on the Effective Connectivity in Human Primary Auditory Cortices)

Ahmad Nazlim Yusoff*, Mazlyfarina Mohamad, Khairiah Abdul Hamid & Aini Ismafairus Abd Hamid

Makmal Pemprosesan Imej Kefungsian (FIPL), Program Pengimejan Diagnostik & Radioterapi

Fakulti Sains Kesihatan Bersekutu, Universiti Kebangsaan Malaysia, 50300 Jalan Raja Muda Abdul Aziz, Kuala Lumpur, Malaysia

Siti Zamratol-Mai Sarah Mukari

Jabatan Audiologi & Sains Pertuturan, Fakulti Sains Kesihatan Bersekutu, Universiti Kebangsaan Malaysia, 53200 Jalan Temerloh, Kuala Lumpur, Malaysia

Received: 27 November 2008 / Accepted: 29 November 2010

ABSTRAK

Kajian ke atas sifat kehubungan efektif dalam korteks auditori dilakukan ke atas lima orang subjek Melayu lelaki sihat berumur antara 20 hingga 40 tahun menggunakan pengimejan resonans magnet kefungsian (fMRI), pemetaan statistik berparameter (SPM5) dan pemodelan dinamik penyebab (DCM). Paradigma pengimejan 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 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 korteks auditori kanan dan kiri pada kawasan Brodmann (BA)22, 41 dan 42 melibatkan korteks auditori primer dan sekunder. Tiga kawasan auditori di korteks auditori kanan dan kiri tersebut dipilih untuk penentuan kehubungan efektif melalui pembentukan sembilan model rangkaian. Kehubungan efektif ditentukan ke atas empat daripada lima subjek dengan mengecualikan seorang subjek yang mempunyai koordinat BA22 yang terletak terlalu jauh daripada koordinat BA22 yang diperoleh daripada analisis kumpulan. Keputusan DCM menunjukkan kewujudan kehubungan efektif di antara ketiga-tiga kawasan auditori yang dipilih di kedua-dua korteks auditori. Pada korteks auditori kanan, BA42 dikenalpasti sebagai pusat masukan dengan kehubungan efektif satu arah selari BA42 → BA41 dan BA42 → BA22. Walau bagaimanapun, untuk korteks auditori kiri, pusat masukan adalah BA41 dengan kehubungan efektif satu arah selari BA41→BA42 dan BA41→BA22. Kehubungan di antara kawasan auditori yang mengalami pengaktifan mencadangkan kewujudan lintasan isyarat dalam korteks auditori walaupun semasa subjek mendengar bunyi hingar.

Kata kunci: Kawasan Brodmann; Pemetaan Statistik Berparameter; Pemodelan dinamik penyebab, Pengimejan Resonans Magnet Kefungsian

ABSTRACT

A study on the effective connectivity characteristics in auditory cortices was conducted on five healthy Malay male subjects with the age of 20 to 40 years old using functional magnetic resonance imaging (fMRI), statistical parametric mapping (SPM5) and dynamic causal modelling (DCM). A silent imaging paradigm was used to reduce the scanner sound artefacts on functional images. The subjects were instructed to pay attention to the white noise stimulus binaurally given at intensity level of 70 dB higher than the hearing level for normal people. Functional specialisation was studied using Matlab-based SPM5 software by means of fixed effects (FFX), random effects (RFX) and conjunction analyses. Individual analyses on all subjects indicate asymmetrical bilateral activation between the left and right auditory cortices in Brodmann areas (BA)22, 41 and 42 involving the primary and secondary auditory cortices. The three auditory areas in the right and left auditory cortices are selected for the determination of the effective connectivity by constructing 9 network models. The effective connectivity is determined on four out of five subjects with the exception of one subject who has the BA22 coordinates located too far from BA22 coordinates obtained from group analysis. DCM results showed the existence of effective connectivity between the three selected auditory areas in both auditory cortices. In the right auditory cortex, BA42 is identified as input centre with unidirectional parallel effective connectivities of BA42 → BA41 and BA42 → BA22. However, for the left auditory cortex, the input is BA41 with unidirectional parallel effective connectivities of BA41→BA42 and BA41→BA22. The connectivity between the activated auditory areas suggests the existence of signal pathway in the auditory cortices even when the subject is listening to noise.

Keywords: Brodmann Area; Dynamic causal modeling; Functional Magnetic Resonance Imaging; Statistical Parametric Mapping

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*Corresponding author; email: nazlim@medic.ukm.my