| Patients with amnestic mild cognitive impairment(a MCI)have a very high rate of dementia conversion and are at significant risk for developing Alzheimer’s disease(AD).Even though there is no effective pharmacological treatment for mild cognitive impairment(MCI),this stage is crucial for preventing dementia.As a result,finding effective non-pharmacological treatments is a pressing clinical issue.Our study presents an analysis of two aspects as follows.Firstly,as a key component of many higher cognitive functions,visual working memory(VWM)deteriorates with ageing.Among the various declining cognitive abilities in amnestic mild cognitive impairment(a MCI),impairment in VWM is more prominent and can reliably predict the progression from MCI to AD.Therefore,the first part of this study would explore the cognitive neural mechanisms of VWM impairment in a MCI,focusing on which part of VWM processing is actually impaired in a MCI patients and distinguishing whether their processing is at the encoding or storage stage by EEG.a MCI patients and healthy elderly controls were enrolled and their visual working memory capacity was assessed using a change detection paradigm,and their attention and executive functions were assessed using digit-symbol conversion and Stroop tasks.a MCI patients were found to have significantly lower accuracy and memory capacity for completing VWM tasks and longer reaction times;and mostly seen as extended reaction times for completing Stroop task.Further,the study combined EEG analysis techniques,including Event related potential(ERP)analysis,Event Related Spectral Perturbation(ERSP),functional connectivity analysis(weighted Phase Lag Index(w PLI),etc.)to investigate the impairment of visual working memory and related electrophysiological mechanisms in a MCI patients.The results revealed that a MCI patients experienced various magnitude drops in the VWM-related ERP components,including P1,N2 pc,Contralateral Delay Activity(CDA).θ oscillations in the prefrontal region and αoscillations in the parieto-occipital region were significantly decreased during the VWM processing process,while β-band Event-related synchronization(ERS)was enhanced,and the synchrony of the fronto-parietal connections in the θ and β bands was decreased.Correlation analysis suggested that degree of visual working memory impairment in a MCI patients was closely related to the degree of decline in overall cognitive function,attention and executive function.Our study explored effective non-pharmacological treatment options in the second part.Strong magnetic pulses were used in repeated transcranial magnetic stimulation(r TMS),stimulating the cerebral cortex to maintain and enhance cognitive performance by altering brain activity.r TMS has been used in numerous researches to investigate how to improve memory performance in humans and has produced positive non-pharmacological outcomes since it is non-invasive,highly targeted,effective,safe,and reliable.A crucial component that regulates VWM operations top-down is the Dorsolateral Prefrontal Cortex(DLPFC).This study targeted the DLPFC and explored how the intervention affected patients’ VWM and at which stage of VWM information processing.The study focused on the effects of r TMS intervention on working memory in a MCI patients by comparing the changes in visual working memory in each group after the intervention.r TMS was found to improve the behavioral performance of visual working memory and improve attentional and executive functions in both a MCI patients and healthy elderly controls over a 7-days period.However,the cognitive neural mechanisms by which r TMS improved VWM cognition might differ between the two groups.For a MCI patients,r TMS significantly increased VWM task-related P1,N2 pc,and CDA amplitudes,as well as α oscillations in the parieto-occipital region,enhanced Event-related de-synchronization(ERD)in the β band,and improved frontoparietal connectivity in the β band.In contrast,for healthy elderly controls,the N2 pc and CDA amplitudes were increased andαoscillations in the prefrontal region were enhanced.Correlation analysis showed that the degree of memory capacity improvement in a MCI patients was closely related to the degree of CDA amplitude improvement.Besides,it was found that the degree of attention and executive function improvement was closely related to the degree of improvement of CDA and N2 pc amplitudes.Based on the above research results,this study mainly drew the following conclusions:(1)a MCI patients suffered different degrees of impairment during different VWM processing stages;(2)Visual working memory impairment in a MCI patients may be related to the decreased top-down regulation ability of α oscillations and decreased synchronization of the frontoparietal control network,which affect the allocation of attention resources in a MCI patients,leading to the decreased inhibition ability of irrelevant information,and the decreased ability of selective attention and attentional control.(3)r TMS can improve the working memory of a MCI patients by stimulating DLPFC;(4)r TMS may improve visual working memory by enhancing the top-down regulation of α oscillations,improving the synchronization of frontoparietal control network connections,optimizing the allocation of attention resources,enhancing selective attention,enhancing alertness and sustained attention,and enhancing the ability to suppress irrelevant information. |
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