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Title:	Gandingan intrinsik di antara kawasan korteks teraktif semasa tugasan mendiskriminasi frekuensi nada murni: kajian FMRI ke atas subjek berpendengaran normal
Authors:	Khairiah Binti Abdul Hamid (P54398)
Supervisor:	Prof. Madya Dr. Ahmad Nazlim Yusoff
Keywords:	Korteks Frekuensi nada murni Auditory Dissertations Academic- Malaysia
Issue Date:	6-Dec-2013
Description:	Walaupun telah banyak diketahui mengenai respons korteks auditori normal terhadap nada murni berfrekuensi rendah dan tinggi, pengetahuan mengenai sifat kehubungan antara korteks di luar kawasan auditori semasa tanggapan nada murni dalam senyap dan hingar, secara binaural dan monaural masih berkurangan. Maka, kajian ini dijalankan untuk menentukan sifat pengaktifan dan kehubungan antara korteks semasa tugasan diskriminasi nada murni dan bagaimana ia dipengaruhi oleh frekuensi nada murni, telinga yang menerima stimulus dan hingar latar belakang. Lapan belas subjek berpendengaran normal (9 lelaki bagi tugasan binaural, serta 10 lelaki bagi tugasan monaural) menyertai kajian ini. Tiga sesi pengimejan resonans magnet kefungsian (fMRI) untuk tugasan diskriminasi nada murni yang diberi secara binaural (Bin), monaural kanan (MoR) dan monaural kiri (MoL) telah dijalankan. Subjek diminta mendengar siri 5 nada murni berbeza frekuensi (700, 1000 dan 2000 Hz dibawah kategori frekuensi rendah, dan 3500, 4000 dan 4500 Hz dibawah kategori frekuensi tinggi) yang diberikan secara rawak dalam senyap dan hingar (-5 dB). Mereka kemudiannya dikehendaki mendiskriminasi nada murni pertama dengan terakhir dan memberi respons dengan menekan bebuli getah hanya jika dirasakan kedua-duanya sama. Pengaktifan otak dianalisis menggunakan pemetaan statistik berparameter (SPM) manakala sifat kehubungan pula ditentukan menggunakan pemodelan dinamik penyebab (DCM) dan pemilihan model Bayesian (BMS). Tugasan membeza nada murni mengaktifkan korteks auditori dan beberapa korteks di luar kawasan auditori secara bilateral, membuktikan wujudnya lintasan secara kontra- dan ipsilateral dari sistem subkorteks, walaupun dengan rangsangan monaural. Bagaimana pun, purata peratus perubahan isyarat (PSC) adalah lebih tinggi pada hemisfera kanan (p < 0.001) semasa Bin, MoR dan MoL mencadangkan peranan korteks pada hemisfera tersebut yang lebih dominan dalam pemprosesan stimulus tak verbal seperti nada murni. Nilai PSC bagi girus Heshl (HG) dan girus temporal superior (STG) bilateral yang lebih tinggi semasa mendiskriminasi nada murni berfrekuensi rendah berbanding tinggi menunjukkan bahawa kawasan tersebut lebih sensitif terhadap nada murni berfrekuensi rendah. Kehadiran hingar latarbelakang telah menyebabkan peningkatan nilai PSC pada HG dan STG kanan. Keputusan ini menyokong peranan korteks auditori kanan dalam memproses hingar putih (HG) dan sebagai pusat tumpuan perhatian berkaitan maklumat auditori tak verbal (STG), terutamanya apabila adanya hingar latar belakang. Keputusan BMS mendapati bahawa jaringan kehubungan di antara korteks aktif semasa tugasan mendiskriminasi nada murni adalah berlainan di antara Bin, MoR dan MoL. Kehubungan efektif ketika Bin boleh diterangkan dengan gandingan bersaling di antara STG dengan insula yang terlibat dalam tumpuan perhatian auditori serta hubungan sehala dari STG ke kawasan motor tambahan (SMA) di hemisfera kanan. Tindakan respons mencetuskan kehubungan sehala dari SMA ke korteks motor. Jaringan kehubungan ketika MoR dan MoL mempamerkan corak kehubungan yang berlainan berbanding Bin. Ini berkemungkinan disebabkan oleh peniruan telinga yang dipekakkan pada subjek berpendengaran normal tidak dicapai sepenuhnya untuk rangsangan monaural. Kajian ini menunjukkan bahawa pengecaman, ingatan dan diskriminasi nada murni berupaya mencetuskan kehubungan dari korteks auditori ke korteks luar kawasan auditori seperti insula dan SMA. Hingar latar meningkatkan tumpuan berkaitan maklumat auditori dan berupaya mengubah kekuatan gandingan sedia ada di antara kawasan otak aktif.,Despite extensive knowledge on responses of normal auditory cortices to low- and high-frequency pure tones, knowledge on the connectivity characteristics between the auditory cortex and cortices outside the auditory areas during the perception of pure tones in quiet and in noise, binaurally and monaurally is still lacking. Thus, this study was done to determine the activation and connectivity characteristics between cortices during pure tone discrimination task and how the characteristics are influenced by pure tone frequencies, stimulus-receiving ear and background noise. Eighteen normal hearing subjects (9 males for binaural task, and 10 males for monaural tasks) participated in this study. Three functional magnetic resonance imaging (fMRI)sessions for pure tone discrimination tasks given via 1) binaural (Bin), 2) right monaural (MoR) and 3) left monaural (MoL) were conducted. Subjects were asked to listen to series of 5 pure tones of different frequencies (700, 1000 and 2000 Hz grouped under low frequency category and 3500, 4000 and 4500 Hz under high frequency category) randomly presented in quiet and noise (-5 dB). They were then required to discriminate the first and the last tones and respond by pressing the squeeze bulb only when they felt that both were the same. Brain activations were analysed using statistical parametric mapping (SPM) while the connectivity characteristic was determined using dynamic causal modeling (DCM) and Bayesian model selection (BMS). Pure tone discrimination task activates auditory cortex as well as several other cortices outside auditory areas bilaterally indicating the existence of contra- and ipsilateral crosspaths from the subcortical system, even in monaural stimulation. However, the average percentage of signal change (PSC) was higher in the right hemisphere during Bin, MoR dan MoL (suggesting a more dominant role of the that hemisphere in processing non verbal stimuli such as pure tones. The PSC values for bilateral Heschl's gyrus (HG) and superior temporal gyrus (STG) that were higher during low-frequency pure tones as compared to high-frequency pure tones discrimination suggested that the two areas were more sensitive to low frequency pure tones.The presence of background noise resulted in an increase in PSC values in the right HG and STG. This result supports the role of the right auditory cortex, especially processing of white noise (HG) and as the centre for focused attention regarding nonverbal auditory information (STG), especially with the background noise. BMS results showed that the connectivity network between the activated cortices during pure tone discrimination tasks are different between Bin, MoR and MoL. The effective connectivity during Bin can be explained with reciprocal coupling between STG and insula that were involved in auditory attention and a one-way coupling from STG to supplementary motor area (SMA) in the right hemisphere. Responding elicited a oneway connectivity from SMA to motor cortex. The connectivity network during MoR and MoL portrayed a different connectivity pattern between the activated cortices. This is potentially due to the deaf ear imitation on the normal hearing subjects that was not fully achieved for monaural stimulation. This study has shown that the recognition, memory and discrimination of pure tones are able to elicit connections from auditory cortex to cortices outside the auditory areas such as insula and SMA. The background noise elevates the attention to auditory-related and is capable of changing the strength of existing couplings between activated brain areas.,Master
Pages:	279
Call Number:	WC270.K45g 2013 9 tesis
Publisher:	UKM, Kuala Lumpur
Appears in Collections:	Faculty of Health Sciences / Fakulti Sains Kesihatan

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