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PhD Thesis in Electrical Engineering – Biomedical Engineering:Auditory "Change Detection" Analysis using Integrated Event-Related Potentials and fMRI in Chronic Tinnitus Subjects

Asadpour, Abdoreza | 2019

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 52403 (05)
  4. University: Sharif University of Technology
  5. Department: Electrical Engineering
  6. Advisor(s): Jahed, Mehran; Mahmoudian, Saeid
  7. Abstract:
  8. Tinnitus is commonly referred to the symptom of “ringing in the ear”, and it is scientifically described as the perception of sound in the absence of an acoustic event. This symptom is powerful enough to negatively affect sleep patterns and concentration. The symptoms affect more than forty-five million people only in the US and 10 to 20% of the world population. Management and treatment of subjective tinnitus is an ongoing focus of research activities. Ample evidence suggests that the mechanism of tinnitus involves maladaptive plasticity in both classic and non-classic auditory pathway. The non-classical pathway is referred to multi-modal sensory inputs to the auditory system, limbic system, and extralemniscal paths. One of the theories utilized is based on the auditory sensory-memory deficit and pre-attentive central auditory processing mechanisms.This study considered Mismatch Negativity (MMN) as a common index of auditory sensory or echoic memory, and context-dependent information processing primarily at the level of auditory cortices, and sound discrimination accuracy. Also, cognitive memory was assessed using visual and auditory P300 response with the oddball paradigm. Furthermore, in order to verify the potency of this approach, sound therapy and patients’ electroencephalogram (EEG) was investigated. For MMN evaluation, a Two-Sample Assuming Unequal Variances T-test with significance level of 0.05 was used between tinnitus and Normal Hearing (NH) control groups to determine if the groups have significant differences in the time features. Mean amplitudes of MMN peak in two groups, namely 5 deviants in 1 kHz central frequency and all deviants in 5 kHz frequency, showed lower meaningful MMN peak amplitude in tinnitus compared to the NH group. The Area Under the Curve (AUC) for all deviants in both central frequencies indicated lower mean AUC for tinnitus patients compared to normal control group. Simultaneous EEG-fMRI data was used to create the Dynamic Causal Model (DCM) for EEG and fMRI separately. DCM on fMRI data showed that in 5 kHz central frequency, only primary auditory cortex was active while in 1 kHz central frequency upper regions in the brain were active and these regions were confirmed using DCM for EEG data. T-test with significance level of 0.05 was applied on amplitude and latency of auditory and visual P300 for all EEG channels separately to compare tinnitus and normal hearing groups where the tinnitus group showed meaningful lower amplitude for auditory P300 peak in 3 EEG channels. Also, broadband sound therapy was applied to study the difference of brain activity, a) before fake treatment, b) after fake treatment and c) after the main treatment, using EEG and Visual Analog Scale (VAS) for evaluating Residual Inhibition (RI). Four features were extracted using 4-level wavelet decomposition with Symlet 8 as its mother wavelet. For the “After the main treatment” stage, the mean value of wavelet coefficients for the last wavelet level, which corresponded to delta band of EEG, was lower in the FC3 channel based on Two-Sample T-Test with significance level of 0.01, as compared to the same channel of the “before the treatment” stage, for cases in which decreased tinnitus loudness were reported. These results may indicate the need to search for treatments in defective cortical processes in which this study found
  9. Keywords:
  10. Tinnitus ; Electroencphalogram ; Functional Magnetic Resonance Imaging (FMRI) ; Dynamic Causal Model ; P300 Wave ; Residual Inhibition ; Mismatch Negativity Wave ; Late Auditory Response (LAR)

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