A Study On The Mechanism Of Sleep Deprivation Vulnerability Based On The Changes Of Brain Gray Matter Structure

Sleep deprivation may impair cognitive functions,and the damage degree varies significantly among individuals,which is known as the sleep deprivation vulnerability.Behavioral studies have shown that vulnerability is a trait attribute of humans,but its underlying neural mechanisms are not fully understood.Although previous studies have found that sleep deprivation vulnerability is related to brain functional plasticity,it is still unclear whether there could be plasticity changes of the brain gray matter structure.Therefore,the goals of this thesis are to explore the alteration of brain gray matter structure induced by sleep deprivation and the possible relationships between them and behavioral vulnerability,and to further assess the changes in intrinsic function related to the gray matter structure.Firstly,based on the structural magnetic resonance imaging(MRI),we used the voxel-based morphometry(VBM)to analyze the changes of brain gray matter density before and after24-hours sleep deprivation,and Pearson correlation analysis were then applied for the gray matter's alteration and behavioral indicators.The results showed that the gray matter density increased significantly in parts of the prefrontal cortex after sleep deprivation.In terms of behavior,it was found that the sleepiness of the subjects increased after sleep deprivation,positive emotions decreased while negative emotions increased,and the psychomotor vigilance test(PVT)response rate decreased,indicating decreased alertness.The changes of gray matter density in the prefrontal cortex were positively correlated with sleepiness,as well as the fastest 10% response rate in PVT.This may be a structural "compensatory" mechanism that reflects the plasticity of the brain structural and its resilience under sleep stress.The changes of gray matter density in these brain regions may be the structural basis for changes in behavioral performance.Secondly,based on the images which were obtained from the subtraction of structural MRI before and after sleep deprivation,we analyzed the relationship between the changes of gray matter density at the whole brain level and the changes of behavior indicators.The results showed that the increase of sleepiness after sleep deprivation were significantly positively correlated with the changes of the density in middle cingulate cortex.The increase of negative emotions were significantly positively correlated with the increase of amygdala's density and the decrease of ventromedial prefrontal cortex's density.Previous studies have shown that the neural pathway between the ventromedial prefrontal cortex and the amygdala is the key to control emotions.The former inhibits the production of negative emotions by inhibiting the activity of the amygdala.The contrary correlation trend between amygdala and ventromedial prefrontal cortex with negative emotions found in this thesis could serve as evidence to explain the mechanism of action of this neural pathway.Thirdly,based on the functional MRI data and the brain regions with abnormal structure,we analyzed the functional connectivity(FC)and functional connection density(FCD)changes of these seed points,and their relationship with gray matter density changes.The results showed that the FC between prefrontal cortex and the hippocampus,brainstem,thalamus and amygdala decreased significantly after sleep deprivation.The FC between the putamen and thalamus,cingulate cortex and insular cortex were significantly increased.These results could explain the neural basis of behavioral impairment caused by sleep deprivation and the compensatory mechanism.However,no linear correlation was found between functional changes and structural changes.FCD analysis found that FCD value in the right superior frontal gyrus and the right middle frontal gyrus decreased significantly after sleep deprivation.The significant increase in gray matter density found in the two brain regions could be explained by the brain's compensatory mechanism for maintaining general performance level,but the significant correlation was not found between them.After sleep deprivation,the FCD of the ventromedial prefrontal cortex also decreased significantly,which may lead to a decrease in its inhibitory effect on the amygdala,and then an increase in negative emotions.This finding verifies the effects of sleep deprivation on this neural pathway.In addition,there was a significant correlation between changes of FCD in the insular cortex and changes in its gray matter density.Considering its significant correlation with increased negative emotions,these findings indicate that there were interrelated changes among the structure,function and behavior of this brain region during sleep deprivation.In conclusion,this thesis found that there were differences in the density of brain gray matter before and after sleep deprivation,and the behavioral vulnerability was associated with the alteration of gray matter structure.We hope our findings may provide neuroimaging evidence to further improve our understanding of the neural mechanisms of sleep deprivation vulnerability.