Study On The Effect Of Different Stimulating Light Source Area On SSVEP Resonance Frequency

The resonance frequency of steady-state visual evoked potentials(SSVEP)is the stimulation frequency needed to induce the maximum power response of SSVEP.The resonance frequency of SSVEP is usually called "light driven label" or "frequency label".It can be used as the research and diagnosis target of brain disease dynamics.It has important research and application significance in the prediction or diagnosis of depression,neurodegenerative diseases and other clinical neurological diseases.The change of periodic light stimulation parameters is the key factor affecting the resonance frequency of SSVEP.In this paper,we focus on the effect of the area change of periodic visual stimulation on the resonance frequency of SSVEP under the same condition of other stimulation parameters.Firstly,based on the dynamic analysis of Wilson-Cowan model and bifurcation theory,the equivalent oscillatory network model of visual cortex neurons is established to simulate the effect of different visual stimulation area changes on the resonance frequency of SSVEP output from the equivalent oscillatory network model.Then,by detecting the SSVEP of brain scalp,the light source area of flash stimulation and the resonance frequency of SSVEP are studied experimentally.Finally,the simulation and experimental results are compared to verify the rationality and reliability of the established equivalent oscillation network model of visual cortex neurons,which provides an effective theoretical simulation model for the study of the relationship between the changes of visual stimulation area and the resonance frequency of SSVEP.The specific research work is as follows:1.Based on the bifurcation theory of nonlinear system,the background potential intensity and time constant of the equivalent model of single Wilson-Cowan neuron group are analyzed dynamically,and the corresponding single parameter interval is determined.The simulation results show that the change of model parameters has an effect on the pulse rate of excitation subgroup E and suppression subgroup I and local field potential.According to the simulation results and bifurcation theoretical analysis results,a single Wilson-Cowan neuron group is taken as the basic unit of the cortical network,and the coupling mode is taken as the typical connection mode between the corresponding Wilson-Cowan model of excitation subgroup and inhibition subgroup.Different connection parameters represent the functional connection characteristics between different Wilson-Cowan models,so the equivalent oscillation network model of visual cortex neurons is established.2.Based on the established equivalent oscillation network model of visual cortical neurons,the effect of the change of visual stimulation area on the resonance frequency of the SSVEP response output from the equivalent oscillation network model of visual cortical neurons was studied.The simulation results show that in the range of 1-30 Hz stimulation frequency,the resonance frequency of SSVEP in the model of equivalent oscillation network of visual cortex neuron presents an inverted U-shaped "window" effect with the change of visual stimulation area: when the stimulation area is less than a certain threshold,the resonance frequency increases with the increase of area;when the stimulation area exceeds the threshold,the resonance frequency decreases with the increase of area.When the stimulation area is equal to the threshold,the resonance frequency is the highest.3.In this paper,the periodic flashing LED is used as the stimulation light source.When the radius of light source and the frequency of light stimulation change in the range of 5-9 mm and 6-20 Hz respectively,the effect of the change of stimulation area of different light sources on the resonance frequency of SSVEP is studied.The experimental results show that the resonance frequency of SSVEP is positively correlated with the circle radius when the light source radius is less than 7 mm,and negatively correlated with the circle radius when the circle radius is greater than 7 mm,when the circle radius is 7 mm,the resonance frequency of SSVEP is the largest,that is to say,the curve of SSVEP resonance frequency with the stimulus area of the light source shows an inverted U-shaped change rule of first rising and then falling.4.The results of simulation and experiment show that the SSVEP resonance frequency increases first and then decreases with the increase of visual stimulation area.As the visual cortex and scalp of the brain detect that SSVEP has the same qualitative rule with the stimulation frequency,so within the frequency range of the experiment in this article,the experimental and simulation results are the same for the change rule of SSVEP resonance frequency,which verifies the rationality of the calculation model of the visual cortex neuron oscillation network established in this paper,and also provides a significant theoretical and experimental basis for the in-depth study of the impact of visual stimulus area change on SSVEP resonance frequency.