| To those investigators who engaged with ophthalmology and neurology, it is true that visual evoked potential (VEP) using pattern reversal stimuli is the most widely used and with the highest stability methods to detect human visual system function. Such factors as the check size, the reversal frequency and the check brightness/contrast and so on will affect the detection of VEP. To grasp the principle of such influence can help us to know the function of our visual cortex more broadly. In addition, EEG can't localize the origin of the action precisely on human visual cortex. Magnetoencephalography (MEG) is a new technique advent in the late 1960s, which can be used as a non-invasive method to study functional activity of human brain. MEG can examine the magnetic field coming from the changing potential of postsynaptic membrane. By using equivalent current dipole model (ECD), the cortex source of the field can be localized. Unlike EEG, the magnetic field tends not to be affected by the conductivity of different media. Its localization reliability has been proved by a large number of researchers. Because the magnetic fields produced by neuronal currents are not attenuated by inhomogeneous conducting intervening layers, MEG are not affected by the multiple tissue layers between the brain and the external surface of the head. Its spatial resolution is about 2 mm and temporal resolution is about 1 ms. Thus MEG can monitor human brain activity dynamically in real time and describe the magnetic field position precisely. The emerging of MEG has made human to know the work principle of our visual cortex from another new angle of view. Because of the brilliant temporal and spatial susceptibility, magnetic source imaging could be acquired, which the origin of visual functional area could be recognized by overlapping the dipole source location withbrain structural images. MEG is widely used in basic research and clinical practice for its invasiveness and accurate depicting of the location in which the magnetic fields originated. The field evoked by visual stimulus is termed visual evoked field (VEF).Visual stimulus can be divided into pattern and non-pattern stimulus. It is discovered in recent science research that the variance of brain reaction are great not only in the traditional VEP but also in VEF. The human brain activity to the checkerboard and bars, however, is relatively steady. Compared with the non-pattern stimulus of same parameters, the differentiation of the VEF is small in both intra-individual and inter-individual cases. The pattern reversal stimulus has two kinds of elements, such as black and white checkerboard or bars, alternating in certain frequency. Due to the unchanged number of black and white elements within the stimulus field, the average luminance during the stimulation stays fixedness. In this paper, MEG is used to test the activity of human brain to the checkerboard pattern reversal stimulus, especially in those suspects as below: ⑴ the effect of spatial frequency on VEF; ⑵ the effect of temporal frequency on VEF; ⑶ the effect of contrast and luminance on VEF; ⑷ the VEF of various visual field; ⑸ the MEG study of homonymous hemianopia patients. It is helpful to acknowledge the effect of these parameters to VEF activity to understand the function of visual cortex more comprehensively. Notice of functional lost of visual cortex and rehabilitate mechanism could be a good help in evaluating the reconstruction of it, estimating the efficiency of healing exercise objectively, and providing the objective foundation in seeking the perfect healing means. Part 1: Magnetoencephalography Research on Effects of Spatial Frequency on Pattern Reversal Visual Evoked Magnetic FieldObjective: To describe the characteristic of the visual evoked magnetic field to half field pattern reversal stimuli and evaluate the effectsof spatial frequency on pattern reversal visual evoked field (PR-VEF) by using magnetoencephalography. Methods: Left half field white and black pattern re...
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