Spatial Frequency-related Functional Alterations In The Visual Cortices Of Patients With Pathological Myopia Based On FNIRS

ObjectiveIn this study,we designed Checkerboard reversal visual stimulation task based on clinical VEP parameters,and verified that the task which combined with functional nearinfraredspectroscopy(f NIRS)technique could successfully detect the hemodynamic changes in the occipital visual cortex of human brain.In addition,this technique was used to investigate the function of cerebral cortex in pathologic myopic(PM)patients with different levels of myopic macular disease under low and high spatial frequency of visual stimulation.MethodsFrom December 2019 to December 2020,a total of 17 eyes of 34 normal adult volunteers were recruited as the normal control(NC)group.A total of 38 eyes of 23 PM patients which meet the inclusion criteria were collected from the ophthalmic fundus outpatient department of the Eye Hospital Affiliated to Shandong University of Traditional Chinese Medicine.According to their fundus lesions,they were divided into PM-A group(grade 2 and grade 3 myopic macular lesions)and PM-B group(grade 4 myopic macular lesions).There were 20 eyes in the PM-A group and 18 eyes in the PM-B group.All subjects were required to sign written informed consent prior to taking the test.The visual stimulus material in this experiment is black and white checkerboard with two specifications,low spatial frequency(1° perspective)and high spatial frequency(15 ’perspective),drawn by Photoshop drawing software.The visual task process consisted of eye closing preparation period(10s)+ black screen baseline period(30s)+ black and white reversal checkerboard visual stimulation period(2Hz reversal)(30s)+ black screen recovery period(50s).E-Prime 2.0 software was used in the experiment to control the automatic presentation of visual tasks.In the relatively closed and quiet dim testing room,participants sit 1 m in front of the computer screen,watch 15 ’and 1 ° angle turn black and white checkerboard stimulation tasks,watch at the same time use the ETG-4000 brain function imaging device.Quantitative real-time synchronous acquisition participants included cerebral oxygenation hemoglobin(Oxy-Hb),deaeration hemoglobin(Deoxy-Hb)and the concentration of total hemoglobin(Total-Hb)changes.The NIRS＿SPM8 toolbox based on Matlab software was used for the noise reduction filtering and baseline correction pretreatment of the subjects’ f NIRS data,and then the SPSS 17.0 software package was used for statistical analysis of the later data.Results1 FNIRS results in normal subjects:1.1 Distribution of activated channels of brain function during low spatial frequency checkerboard stimulationAccording to matching t test results of the beta value statistics based on the baseline and excitement period of the subjects,the results showed that the P value of the channel 5,10,13,14,15,16,17,18,19,20,21 and 22 was less than or equal to 0.05,which suggested that during the period of stimulation,these channels were significantly activated in the cerebral cortex(P > 0.05,no statistical significance).1.2 Distribution of the activated channels of brain during high spatial frequency checkerboard stimulationMatching t test of the beta value obtained from the baseline period and excitement period of the subjects showed that the P value of channel 1>5>12>13>14>15>16>17>18>19>20>21 and 22 was less than or equal to 0.05,which suggested that during the period of stimulation,these channels were significantly activated in the cerebral cortex(P > 0.05,no statistical significance).1.3 Comparative analysis of ROI under checkerboard visual stimuli with different spatial frequenciesAccording to the positioning of the VPen system,10 to 22 channels were chosen as interested area(ROI).For each subject?the beta value within the ROI of the baseline and stimulation stage were averaged and evaluated.The comparation results between the low spatial frequency and high spatial frequency was analysed by paired sample t test.The results showed no statistical difference in the beta value during the baseline period between two different spatial frequencies in normal subjects @t=1.031?P=0.310A0.05 B.There was also no significant difference in C values between the two spatial frequency visual tasks during the stimulation period @t=0.687?P=0.497A0.05 B.In the two spatial frequency stimulation experiments,typical hemodynamic changes were observed and was consistent with previous studies,that is,the concentrations of Oxy-Hb and Total-Hb increased significantly during the stimulation period,while the concentrations of Deoxy-Hb decreased significantly,which confirmed the rationality of the design of the visual task in this experiment.2 Comparison of FNIRS studies in patients with pathological myopia:2.1 Distribution of activated channels of brain function during low spatial frequency checkerboard stimulationPaired t test was conducted for the C values of subjects in the PM-A group during baseline and stimulation periods.Results showed that PD0.05 in channels 12,14,15,17,18,19 and 22,which indicated a statistical difference.While the other channels showed no statistical significance.Paired t test was conducted for the C values of subjects in the PMB group during baseline and stimulation periods.Results showed that PD0.05 in channels17>19>21 and 22,indicating a statistical difference,while the other channels showed no statistical significance.The results showed that there was an activation in the cerebral cortex in both groups during the stimulation,but the number of activation channels was significantly reduced compared with the normal group.2.2 Distribution of activated channels of brain during high spatial frequency checkerboard stimulationPairedt test was conducted for the C values of subjects in the PM-A group during baseline and stimulation periods.Results showed that PD0.05 in channels 13>15>17>18and 20,indicating a statistical difference,while P > 0.05 in the other channels.Paired t test was conducted for the C values of subjects in the PM-B group during baseline and stimulation periods.Results showed that PD0.05 in channels 14,indicating a statistical difference,while P > 0.05 in the other channels.The results showed that there was an activation in the cerebral cortex in both groups during the stimulation,but the number of activation channels was significantly reduced compared with the normal group.2.3 Comparison of ROI in NC group,PM-A group and PM-B group under low spatial frequency checkerboard stimulationIntergroup independent sample t-test was conducted for the mean β values of all channel stimulation periods in the ROI of subjects in the NC group,PM-A group and PM-B group,and the results showed that there were significant differences between the PM-A group and the NC group @t=2.693?P=0.010D0.05 B,and the activation amount was significantly lower than that of the NC group.There were significant differences between the PM-B group and the NC group @t=2.740?P=0.010D0.05 B,and the activation amount was significantly lower than that of the NC group.There was no statistical difference between PM-A group and PM-B group @t=0.523?P=0.604 > 0.05 B.2.4 Comparison of ROI in NC group,PM-A group and PM-B group under high spatial frequency checkerboard stimulationIntergroup independent sample t-test was conducted for the mean β values of all channel stimulation periods in the ROI of subjects in the NC group,PM-A group and PM-B group.The results showed that there were significant differences between the PM-A group and the NC group @t=3.091?P=0.003D0.05 B,and the activation amount was significantly lower than that of the NC group.There were significant differences between the PM-B group and the NC group @t=3.484?P=0.001D0.05 B,and the activation amount was significantly lower than that of the NC group.There was no statistical difference between PM-A group and PM-B group @t=0.604?P=0.550 > 0.05 B.2.5 Comparative analysis of ROI under different spatial frequency checkerboard visual stimuliPair-t-test was carried out on the β mean values of all channels in ROI of subjects in PMA group under visual stimuli of two different spatial frequencies.The results showed that the activation of Oxy-Hb in cerebral cortex of subjects in PM-A group under visual stimuli of high spatial frequency was lower than that under visual stimuli of low spatial frequency,but there was no statistical difference between the two @t=0.721?P=0.480 > 0.05 B.Pairt-test was carried out on the β mean of ROI channel during the stimulation period of subjects in PM-B group under two different spatial frequency visual stimulis,and the results showed that the activation degree of oxy-Hb in cerebral cortex of subjects in PM-B group under high spatial frequency visual stimuli was lower than that under low spatial frequency visual stimuli,but there was no statistical difference between the two groups（t=0.654?P=0.522 >0.05 ）.Conclusion1 In the experiment of FNIRS combined with visual task stimulation,the 2Hz black and white inverted checkerboard can cause relatively significant response of cerebral cortex.The visual stimulation task can be widely used in research of FNIRS in visual related fields and provide patients with real-time synchronization visual cortex oxygen content parameters under visual task stimulation.2 Compared with the NC group,the Oxy-Hb activation level of cerebral cortex was significantly decreased in PM-A group and PM-B group under low and high spatial frequency visual stimulation.As a kind of late onset ophthalmopathy,abnormal PM visual experience and fundus lesions can weaken the functional activity of the cerebral cortex.3 There was no significant difference in the visual stimulation of low and high spatial frequencies between PM-A group and PM-B group,which was inferred to be caused by the pathological site of fundus and poor visual acuity in the two groups.4 FNIRS technology can be effectively applied to the study of the functional characteristics of human visual cortex,to provide experimental basis for the study of brain functional activities in patients with visual path-related diseases with abnormal visual experience,and to develop a new method.