Spatial Working Memory In Normal Subjects And Schizophrenia Patients: A FMRI Study

Part I Dynamic cortical network of n-back spatial working memory task in normal subjects:A study about effects of memory load with fMRIObjective:With fMRI and n-back spatial working memory task, to explore the neural basis of working memory firstly. Second, within the scope of working memory capacity of normal subjects, to explore the neural substrate of unconstrained memory capacity via analyzing load dependent effects of brain activity in working memory related areas. consequently to discuss the physiological basis of constrained memory capacity.Materials and Methods:18 normal subjects received fMRI with a n-back spatial task, n=1, n=2, n=3 task are employed. Low-load working memory task (i.e. lback task), moderate-load working memory task (i.e.2back task), and high-load working memory task (i.e.3back task) were performance independently. Reaction time and accuracy were recorded across three different load task respectively, and SPSS 17.0 version was used to perform statistical calculations. A p value of less than 0.05 was viewed as significantly difference. Preprocessing, statistical analysis and result display of functional data were performed using SPM5. One sample t-tests of basic model were used to perform group analysis. Two-sample t-tests were used to perform inter-group contrast. Statistical analyses included:group effects analysis of n-back task in normal subjects; Group analysis across three different load task in NO. To explore load dependent effects of WM related brain regions, lback vs 2back,2back vs 3back,3back vs 1back inter-group contrast were performed in NO respectively. Results:Relative cortical regions in the n-back spatial task were defined: bilateral DLPFC (BA9/46), bilateral PPC (BA7/40), bilateral VLPFC (BA44/45/47), bilateral LPMA (BA6/8), dorsal cingulate/SMA/MPMA (BA6/8/32), bilateral rostral prefrontal cortex and frontal pole (BA10). In addition, bilateral cerebellum, left basal ganglia region and thalamus region also demonstrated activity. In NO, across three different load task, bilateral DLPFC, bilateral PPC showed positive load-dependent activity. Those load-dependent areas displayed unconstrained physiological response patterns. And at the highest load task (3back task) superior parietal lobule were recruited.Conclusion:The execution of the spatial work memory is not completed depending on the sole brain area, but on the neural network foundation constituted by the cerebral cortex, the subcortical area and the cerebellum. The main nodes of the neural network is DLPFC (9/46) and PPC(7/40). Within the scope of working memory capacity, as memory load increasing parametrically, the activation of the related brain region are increased distinctly. The activation of DLPFC is increased at the relative lower WM load; the activation of PPC is increased distinctly at the relative high WM load. Moreover, the activation of bilateral cerebellum, basal ganglia and thalamus area is increased distinctly. The results indicated that spatial WM require for stimulation sequence time sorting. Partâ…¡Dynamic cortical network of n-back spatial working memory task in schizophrenia subjects:A study about effects of memory load with fMRIObjective:This article examined neural substrates of working memory impairment in schizophrenia with fMRI and n-back spatial working memory task through the flowing aspects. Firstly, to analyse WM related brain regions for spatial n-back task in schizophrenia subjects. Second, to analyse load dependent effects of brain activity in WM related areas within the scope of WM capacity of schizophrenia (SCH) subjects, and beyond the scope of WM capacity of schizophrenia subjects (SCH). Third, to compare activity difference of WM network between SCH and NO. Then, we characterize activation difference between NO and SCH network across variable load levels. Lastly, to analyse the value of WM network, to verify the feasibility of combing the two networks to differentiate two separate data, one from SCH group and the other from NS.Materials and Methods:18 SCH subjects and 18 normal subjects received fMRI with a n-back spatial task, n=1, n=2, n=3 tasks are employed. On the basis of behavioral performance of 2back task in formal experiment, reaction time and accuracy were recorded across three different load tasks respectively. SPSS 17.0 version was used to perform statistical calculations. Separate Intra-group analysis for SCH and SCH group was performed, also inter-group analysis for the SCH and NS. A P value of less than 0.05 was viewed as significantly difference. Preprocessing, statistical analysis and result display of functional data were performed using SPM5. One sample t-tests were used to perform group analysis. Two-sample t-tests were used to perform intergroup contrast. Statistical analyses included:group effects analysis of n-back task in schizophrenia; Group analysis across three different load task in SCH and SCH; To explore load dependent effects of WM related brain regions, lback vs 2back,2back vs 3back,3back vs lback intergroup contrast were performaned in SCH and/or SCH respectively. To explore brain functional difference, SCH vs NS contrast at three variable load level were also established.Results:Spatial n-back WM related regions of SCH are identical to that of NS. Within the scope from 1-back to 2-back load level in SCH, related regions (bilateral DLPFC, right PPC) activation increased parametrically with WM load. With the scope from 2-back to 3-back, only a little of regions show increasing activation in intensity and range, but behavior performance is decreased instinctively. Compared with NS, SCH activation increase obviously within the WM load from 1-back to 2-back., but decrease obviously within the 3-back level of WM load and consistent with decreasing of behavior performance.Conclusion:Spatial n-back WM related regions of SCH are identical to that of NS. Within the capacity of WM load (1-2back), the activation was significantly greater in the SCH group than the NS group. The results indicated that the increasing activation is compensatory for the inefficient network function consistent with the normal behavior performance with NS. When the MW load reached the capacity of WM, the increase of activation is decreased comparing with NS consistent with the impaired behavior performance and the impaired function of recruiting brain function. The basis of the impaired SCH spatial WM is the inefficient cortex function in the DLPFC and PPC.