Wang Kuo-Wei, Chang Hsiao-Huang, Hsu Chuan-Chih, Chen Kuang-Chao, Hsieh Jen-Chuen, Li Lieber Po-Hung, Lee Po-Lei, Shiao An-Suey
Department of Electrical Engineering, National Central University, No. 300, Jhongda Rd., Jhongli City, Taiwan.
Department of Medical Imaging, Landseed Hospital, No. 77, Kuan-Tai Rd., Taoyuan, Taiwan.
Biomed Eng Online. 2015 Jul 26;14:72. doi: 10.1186/s12938-015-0062-0.
Auditory steady-state response (ASSR) induced by repetitive auditory stimulus is commonly used for audiometric testing. ASSR can be measured using electro-encephalography (EEG) and magnetoencephalography (MEG), referred to as steady-state auditory evoked potential (SSAEP) and steady-state auditory evoked field (SSAEF), respectively. However, the signal level of SSAEP and SSAEF are weak so that signal processing technique is required to increase its signal-to-noise ratio. In this study, a complementary ensemble empirical mode decomposition (CEEMD)-based approach is proposed in MEG study and the extraction of SSAEF has been demonstrated in normal subjects and tinnitus patients.
The CEEMD utilizes noise assisted data analysis (NADA) approach by adding positive and negative noise to decompose MEG signals into complementary intrinsic mode functions (IMF). Ten subjects (five normal and five tinnitus patients) were studied. The auditory stimulus was designed as 1 kHz carrier frequency with 37 Hz modulation frequency. Two channels in the vicinities of right and left temporal areas were chosen as channel-of-interests (COI) and decomposed into IMFs. The spatial distribution of each IMF was correlated with a pair of left- and right-hemisphere spatial templates, designed from each subject's N100m responses in pure-tone auditory stimulation. IMFs with spatial distributions highly correlated with spatial templates were identified using K-means and those SSAEF-related IMFs were used to reconstruct noise-suppressed SSAEFs.
The current strengths estimated from CEEMD processed SSAEF showed neural activities greater or comparable to those processed by conventional filtering method. Both the normal and tinnitus groups showed the phenomenon of right-hemisphere dominance. The mean current strengths of auditory-induced neural activities in tinnitus group were larger than the normal group.
The present study proposes an effective method for SSAEF extraction. The enhanced SSAEF in tinnitus group echoes the decreased inhibition in tinnitus's central auditory structures as reported in previous studies.
由重复性听觉刺激诱发的听觉稳态反应（ASSR）常用于听力测试。ASSR可通过脑电图（EEG）和脑磁图（MEG）进行测量，分别称为稳态听觉诱发电位（SSAEP）和稳态听觉诱发场（SSAEF）。然而，SSAEP和SSAEF的信号水平较弱，因此需要信号处理技术来提高其信噪比。在本研究中，在MEG研究中提出了一种基于互补总体经验模态分解（CEEMD）的方法，并在正常受试者和耳鸣患者中证明了SSAEF的提取。
CEEMD利用噪声辅助数据分析（NADA）方法，通过添加正负噪声将MEG信号分解为互补固有模态函数（IMF）。对10名受试者（5名正常受试者和5名耳鸣患者）进行了研究。听觉刺激设计为载波频率1kHz、调制频率37Hz。选择左右颞区附近的两个通道作为感兴趣通道（COI），并分解为IMF。每个IMF的空间分布与一对左右半球空间模板相关，该模板由每个受试者在纯音听觉刺激中的N100m反应设计而成。使用K均值法识别空间分布与空间模板高度相关的IMF，并使用那些与SSAEF相关的IMF来重建噪声抑制后的SSAEF。
从CEEMD处理后的SSAEF估计的电流强度显示出比传统滤波方法处理的更大或相当的神经活动。正常组和耳鸣组均表现出右半球优势现象。耳鸣组听觉诱发神经活动的平均电流强度大于正常组。
本研究提出了一种有效的SSAEF提取方法。耳鸣组增强的SSAEF与先前研究中报道的耳鸣中枢听觉结构中抑制作用降低相呼应。
