Dissertation > Medicine, health > Ophthalmology

Steady - state visual evoked response detection technology and application

Author HuangYingLing
Tutor YaoDeZhong
School University of Electronic Science and Technology
Course Biomedical Engineering
Keywords vision system steady-state visual evoked potentials (SSVEP) neuronal magnetic field neuronal current MRI (nc-MRI)
Type Master's thesis
Year 2010
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Steady-state evoked responses (SSVER) are evoked responses induced by visual stimuli at constant intensity and frequency, with a stationary spectrum matches the stimuli or its harmonics. The cortical potentials of the SSVER are named steady-state visual evoked potentials (SSVEP). Since SSVEP have strong anti-interference characteristic, unavoidably, more and more researchers apply SSVEP to the study of the visual neural mechanisms. However, present brain imaging techniques (such as EEG/ MEG/fMRI) generally represent a balance between the high spatial and temporal resolution, which limits the development of the research of SSVEP. In this work, we will use SSVEP to investigate the visual neural mechanisms and propose a novel detection technique. The main contents are as follows:1. By using the constant intensity but different frequencies flickering visual stimuli to monocular and binocular, we collected the EEG data and investigated the amplitude and phase of SSVEP in different stimuli condition. The results showed that: with the stimuli frequency increased, SSVEP signal shows a trend of instability; both in monocular and binocular situation, the right and left occipital lobe have the same activity intensity and phase synchronization, which indicate that interhemispheric functional synchronization is the first step of the visual information processing; when our two eyes stared separately at similar object, the visual cortex will integrate the visual information by synchronization to form a single and stable perception, and this integration does not require high-level visual processing.2. Since the limitations of the present brain function testing technologies, we proposed neuronal current MRI (nc-MRI) as a new imaging method with high spatial and temporal resolution to directly map the magnetic field which caused by neuronal activities. We explored the feasibility of nc-MRI by theoretical simulation and experimental method. Our simulation results showed that the existence of dendrite branch can enhance the detectability of neuronal current magnetic field by MRI directly. The signal phase shift is enlarged but instable and the magnitude signal may be strong enough for a typical MRI voxel to be detected. We suggest making further effort to measure the magnitude signal which may induce large effect in an nc-MRI experiment. However, in our application of nc-MRI experimental study, we can not detect any neural activities induced by SSVEP or alpha wave signal. The reason is that the nc-MRI signal may be disturbed by other artifacts such as BOLD (blood oxygen level dependent) and can not be detected.

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