| Objective:Working memory is the ability to temporarily store and process stimulus information,which is the basis for the realization of higher cognitive functions and is essential for older adults to successfully complete daily activities and maintain independence in life.Studies have shown that long-term regular physical activity is effective in delaying working memory decline in older adults,but the underlying neural mechanisms have not been clearly revealed.Therefore,this study aimed to investigate the working memory characteristics of the elderly with long-term physical activity and its relationship with prefrontal gray matter volume and sulcus depth,and to provide stronger evidence for the neural mechanism of exercise delaying working memory decline in the elderly.Methods:Sixty-two physically healthy individuals aged 60-75 years with normal cognitive function were recruited and screened from a community in Shanghai.Subjects who exercised regularly in the past year and achieved moderate to heavy exercise were divided into an exercise group(n=32)and subjects who did not exercise regularly were divided into a control group(n=30)according to the Physical Activity Rating Scale(PARS-3).Using GT3X+accelerometer to measure subjects’physical activity.A digital n-back task(n=0,1,2)was used to measure working memory response time,accuracy,discrimination,and response tendency.Structural magnetic resonance imaging and the region-of-interest-based VBM method and the whole-brain-based SBM method were used to measure subjects’brain gray matter volume and sulcus depth,respectively,and the gray matter volume values of brain regions with significant group differences and n-back task performance were extracted for Pearson correlation analysis and Bootstrap mediation effect test.Results:(1)The behavioral results showed that the older adults in the exercise group had significantly higher accuracy(F(1,56)=10.93,p=0.002,η_p~2=0.16)and discerning power(F(1,56)=9.15,p=0.004,η_p~2=0.14)on the n-back task than the non-exercise group.n=0 condition showed a non-significant difference in accuracy between the two groups(p=0.66),n=1 condition showed a significantly higher accuracy than the non-exercise group(p=0.02),and n=2 condition showed a further increase in the difference in accuracy between the two groups(p=0.002).The between-group differences in response time between the two groups were not significant(F(1,56)=1.93,p=0.17,η_p~2=0.03).(2)The results on gray matter volume showed that subjects in the exercise group had larger gray matter volumes in the left precentral gyrus,left supplementary motor area,left superior frontal gyrus(dorsolateral),right superior and middle frontal gyrus,right inferior frontal gyrus(opercular part),gyrus rectus,anterior and middle cingulate¶cingulate gyri than the non-exercise group(FWE_c ps<0.05),and the gray matter volumes in these specific brain regions were all significantly and positively correlated with the accuracy of the 2-back task(r=0.26～0.48,all ps<0.05).(3)The results on sulcus depth showed that the sulcus depths in the left insula(INS,insula)and the right pericalcarine cortex and precuneus were significantly deeper in the exercise group than in the non-exercise group(FWE_p ps<0.05),and the sulcus depths in the right pericalcarine/precuneus was significantly and positively correlated with accuracy on the 2-back task(r=0.36,p=0.005).(4)The results of the mediating effect analysis showed that the pathway of moderate-to-vigorous physical activity can positively predict working memory performance through the mediation of right anterior and middle cingulate gray matter volume(F(8,51)=3.55,p<0.01),with the mediating effect accounting for 60%of the total effect.Conclusions:(1)older adults with long-term physical exercise have better working memory than the non-exercise group,especially under conditions of high memory load;(2)older adults with long-term physical exercise have larger gray matter volumes in the left precentral gyrus,left supplementary motor area,bilateral superior frontal gyrus and right middle frontal gyrus,right inferior frontal gyrus,right rectus gyrus,and right anterior and middle cingulate gyrus than the non-exercise group;(3)older adults with long-term physical exercise have deeper sulcus depths in the left insula and right pericalcarine cortex/precuneus than the non-exercise group;(4)The neural mechanism of exercise for working memory may involve the protective effect of exercise on gray matter volume in precentral gyrus,supplementary motor area,superior and middle frontal gyrus,inferior frontal gyrus,rectus gyrus,anterior and middle cingulate gyrus as well as sulcus depth in the pericalcarine/precuneus,especially the gray matter volume in the right anterior and middle cingulate gyrus may be a key brain area for exercise to predict working memory ability. |
