| Working memory(WM)refers to a limited system that provides for the temporary storage and manipulation of information.Working memory consists of four subcomponents: a central executive system for attentional control,a phonological loop for the storage and manipulation of verbal materials,a visual-spatial sketchpad for the object and spatial information and an episodic buffer for storage of information.The visual-spatial sketchpad is called “visual working memory”(VWM)and has two subsystems: one for object working memory(OWM)processing,object information like the color,pattern and texture.And one for spatial working memory(SWM)processing spatial information,such as guidance of motor movements toward objects,spatial location of objects,and the spatial relationship among objects.Some experimental paradigms focused on the capacity of spatial working memory,among which “N-back” paradigm was used to explore the capacity of spatial working memory and the neural mechanism of spatial working memory.With the development of functional magnetic resonance imaging(fMRI)technics,researchers have made many achievements in the field of spatial working memory.There are crucial brain areas in “dorsal pathway” including dorsal lateral prefrontal cortex(DLPFC)and posterior parietal cortex(PPC),which are often seen in fMRI analyses and considered to be important for spatial working memory.In the anatomical study,some studies indicated that the schizophrenia patients deficit of spatial working memory are associated with reduce of frontal grey matter volumes(GMV)compared with controls.In 2013,researchers used voxel-based morphometry(VBM)on the structural MRI data to measure the GMV of cortical areas with a significant correlation with individuals' spatial working memory capacity.They found positive correlations between individual spatial working memory ability and grey matter density(GMD)in bilateral inferior parietal lobule(IPL)and right middle frontal gyrus(MFG).Their results are consistent with previous studies(used fMRI)showing that these brain regions are consistently recruited during the maintenance of spatial information,further indicated that individual with greater GMD in IPL and right MFG are able to maintain a greater amount of spatial information in working memory.However,there are still few studies from structural perspectives of spatial working memory.Therefore,this study wants to know whether it is possible to combine voxel-based morphometry(VBM),resting-state functional connectivity(rsFC)and multivariate pattern analysis(MVPA)methods to explore the structural mechanism behind the spatial working memory and to check the possibility of using structural features as a biomarker in predicting individual spatial working memory ability.Spatial working memory will be affected by many factors including sex factor,fMRI studies indicated that male and female activated different brain regions during spatial working memory task,few studies have explored whether there are gender differences of spatial working memory from a structural perspectives.We will also explore the specific structural mechanisms related to the gender differences in the spatial working memory.Secondly,anxiety is a common emotional state in life.Severe anxiety will not only lead to hyperactivity of the vegetative nervous system,but also cause difficulty in attention,reducing the ability of social activity,reducing the association and memory,and reducing work efficiency.The influence of anxiety on spatial working memory has also been explored.Processing efficiency theory(PET)proposed by Eysenck and Calvo(1992)suggests that anxiety will affect the two components of working memory including central executive system and phonological loop,and won't affect spatial working memory.Some studies support this theory,Hadwin and his colleagues explore the relationship of anxiety and working memory,the result indicated that no differences were found between high and low anxiety groups in task(associated with phonological and central executive components of WM)accuracy;however,high anxiety group took longer time to complete the task compared with low anxiety.No significant differences in both accuracy and response time were found for spatial working memory task.However,the results of other studies indicated that anxiety can reduce the performance in spatial working memory task.In 2003,a research pointed that the threat-evoked anxiety will affect the spatial working memory performance,the more anxiety reported by participants,the more impaired on the spatial working memory task.In view of this,this study also explores whether spatial working memory is affected by anxiety.Based on these,we will carry out two studies to answer the questions above.In study 1,60 subjects participated in spatial 2-back task and then collected their T1 structure images and resting-state MRI images.We used voxel-based morphometry(VBM)combined resting functional connectivity(rsFC)and multivariate voxel pattern analysis(MVPA)methods to explore the structural mechanism behind spatial working memory.Using ANOVA analysis to explore the specific structural mechanisms related to the gender differences in spatial working memory.As a result,we found that the grey matter density(GMD)of middle frontal gyrus(BA46)and middle temporal gyrus(MTG)were correlated with spatial working memory ability.Moreover,we found that resting functional connectivity between right middle frontal gyrus and the left superior frontal gyrus(SFG),right supplementary motor area(SMA)are related with spatial working memory capacity,with the higher the connectivity shows,the higher the spatial working memory ability was.Then,we used the MVPA(SVM)machine learning method and then found that GMD of the right middle frontal gyrus could distinguish the higher spatial working memory group with an accuracy of 86.67% and the mean accuracy of 60%.These evidences proved that neural mechanism behind spatial working memory including some important brain areas,i.e.,superior frontal gyrus,middle temporal gyrus,supplementary motor area and middle frontal gyrus.Finally,we used ANOVA analysis and then found in spatial working memory larger GMD of the left middle frontal gyrus and right fusiform gyrus in male while the larger GMD of the right middle frontal gyrus,left middle temporal gyrus and precentral gyrus in female.In study 2,the effects of anxiety on spatial working memory were explored.All participants complete the < State-Trait Anxiety Inventory,STAI >,which composed of< State Anxiety Inventory,SAI> and < Trait Anxiety Inventory,TAI >.Participants were divided into high or low anxiety groups according to the score of < State Anxiety Inventory,SAI >.Then,using the Independent-sample t Test analysis to explore whether anxiety will affect spatial working memory.We found that there is no difference in performance effectiveness(accuracy)and processing efficiency(response time)of spatial working memory task through compared the two anxiety groups.In summary,this study found that the middle frontal gyrus and middle temporal gyrus are critical brain regions of spatial working memory,and the middle frontal gyrus could be used as a biomarker in predicting high spatial working memory ability.The functional connectivity between middle frontal gyrus and superior frontal gyrus,supplementary motor area are positively associated with spatial working memory ability,which indicated that the superior frontal gyrus and supplementary motor area are crucial brain regions in spatial working memory;Gender difference exist in spatial working memory,larger GMD of the left middle frontal gyrus and right fusiform gyrus in male while larger GMD of the right middle frontal gyrus and left middle temporal gyrus in female.Besides,performance effectiveness(accuracy)and processing efficiency(response time)of the spatial working memory task may be not affected by anxiety. |
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