聽性穩態磁場(Steady-State Auditory Evoked Field, SSAEF)是利用連續穩態的聲音刺激，大腦聽覺皮質層所誘發出來的反應磁場，此誘發磁場可做為探討大腦聽覺功能區的指標。然而，聽性穩態磁場的反應強度偏低且帶有許多雜訊，為了提高其訊雜比，我們使用經驗模態分解法(Empirical Mode Decomposition, EMD)來處理此訊號，這項技術能可適性的將聽性誘發磁場萃取出來，以得到大腦聽覺皮質層的活化資訊。 本研究開發以經驗模態分解法為基礎的大腦聽覺皮質誘發磁場分析技術，並應用此技術於耳鳴醫學(tinnitus)的應用探討。臨床上耳鳴患者目前缺乏客觀的診斷及療效評估工具，且過去文獻研究於聽覺損失患者，發現了相異於正常人的腦波聽覺誘發電位，可見耳鳴並非單純的周邊聽神經問題，可能與大腦半球間相互抑制作用降低，以致雙耳交互作用失調產生的病灶有關，我們可經由觸發大腦聽覺皮質層所誘發的反應磁場，加以分析研判之。首先以腦磁圖(Magnetoencephalography, MEG)收集耳鳴患者(實驗組)與健康受試者(對照組)的聽性誘發反應數據，再以經驗模態分解法(EMD)萃取其訊號，最後使用偶極子磁場源進行波源定位(source modeling)，以達到最佳的聽性誘發反應用於耳鳴醫學研究的完整呈現。 希望了解大腦聽覺皮質層之功能重組，及可能的預後參考價值。期待能在耳鳴臨床研究之腦訊號技術平台，提供診斷與療效評估工具之發展，有更進一步的貢獻。 Steady-state auditory evoked field (SSAEF) is a technique which utilizes magnetoencephalography (MEG) to measure the magneto-physiological responses evoked by repetitive auditory stimuli. SSAEFs have been widely used in clinical application and suggested as a clinical idex for diagnosing the function of auditory cortex in human brain. Nevertheless, the SSVEP is susceptible to be affected by task-irrelevant noise and may sometimes deteriorate the correctness in clinical diagnoses. Accordingly, this study aims to develop an empirical mode decomposition (EMD) – based technique to extract SSAEPs so that the signal-to-noise ratio (SNR) of SSAEP can be greatly improved. The efficacy of the proposed method has been applied to study clinical tinnitus patients. The genesis of tinnitus is still unclear and lacks of a reliably objective procedure for diagnosis in clinics. Recent studies have shown the auditory evoked potential / field (AEP/AEF) in patients with tinnitus are deviant from normal subjects. These evidences imply the pathogenesis of tinnitus might be associated with the central auditory plasticity, i.e., the functional reorganization of the auditory cortex, rather than the dysfunction of peripheral auditory sensory networks. In this study, we apply the concurrent measurements of auditory steady-state fields (SSAEFs) to investigate the profound signal processing of the interhemispheric inhibition and binaural interaction. With the localization of auditory-related neural sources by applying electric current dipole (ECD), the proposed EMD-based method may be a powerful tool to shed light on studying the development of tinnitus.
