| Functional near-infrared spectroscopy (fNIRS) is a novel technology for noninvasively monitoring brain function, which has many advantages, such as nonionizing radiation and portability. It is of great importance with broad prospects for application. However, the development of fNIRS technology is restricted by the weakness of the theoretical study on light propagation, and its application is just at the beginning. This research improved the fNIRS technology by resolving the theory problem, explored its application and its synchronization technology, and finally conducted brain function researches based on dual-mode measurements of fNIRS and event-related potentials (ERPs). The main research contents and creative points are as follows:(1) A Monte Carlo model for photon migration in 3-D voxelized media is proposed and coded as the software named MCVM. In this model, a 3-D matrix with identification index of tissue type is employed to describe the tissue structure; each photon is automatically injected referring to the spatial relationship between light injection center and media surface; a voxel-size-dependent pseudo continuous absorption weighting is established; voxel crossings are geometrically determined; the mathematical model for the interactions between the photon and 3-D voxel boundaries is established; the concept of sampling interval is introduced to realize the steady-state and time-resolved simulation; the numerical solutions for convolution and photon distribution methods are provided to compute the effect of light beam. The precision, flexibility, and stability of MCVM have been fully tested. MCVM is also of low application limitation, high speed, easy to use and concise coding, which serves as a novel tool for researches related with light propagation.(2) Based on the considereation that Visible Chinese Human (VCH) most realistically represented the human anatomical structure, VCH and MCVM are combined to set up a platform to acquire, visualize, and analyze the properties of light transport in human body. By using this platform, the design parameters of fNIRS is optimized, its measurement algorithm is determined, its practical issues are quantitatively analyzed, and its signal analysis method and code package is given. Accordingly, the reliability and accuracy of fNIRS is improved. (3) The applications of fNIRS in brain function evaluation, mechanistic investigation and disease recognition are explored.â‘ Working memory in four different tasks is evaluated in real-life situation. The brain activation patterns are validated by the previous fMRI researches and the positive correlation between oxygenation amplitude and task load is observed.â‘¡The hemodynamic response in the prefrontal cortex (PFC) under verbal working memory is investigated. The gender specificities among the hemodynamic parameters are identified. Further findings include females'more focused and weak activation in PFC with the same level of behavioral performance as males and females' only brain-behavior correlation, which contributes to the revelation of gender mechanism.â‘¢The dyslexia children' hemodynamic response in the left PFC is explored under the Chinese character pronunciation task. The abnormal hemodynamic response and low-level supplies of blood and oxygen are found in dyslexia children, which are provided as novel proofs to recognition and mechanism research of dyslexia.(4) A nondestructive synchronization technology of fNIRS is proposed and two cognitive functions are researched with fNIRS-ERPs. Both researches provided narrow scope of the source location. Moreover, a phenomenon is observed in the activation area of visual nonselective attention that fNIRS signal occurred before related ERPs waves and amplified rightly after the disappearance of the ERPs signal, which is important for revealing the neurovascular coupling; in the whole resolving of the conflict under Chinese character-color Stroop effect, the relationship among detected areas in PFC on Stroop effect size interpreted by the ERPs integral wave is consistent to that by fNIRS signal. It indicates that PFC activated during the whole conflict-processing, which is novel beyond the argument over which step does PFC act in the conflict processing.
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