The Effects Of Tai Chi Practice On The Prefrontal Cortex Activation And Postural Contol Ability During Dual-Task Obstacle Negotiation In Older Adults

Objective:With aging,the cognitive function of the prefrontal cortex declines,postural control weakens,and fall risk increases in older adults.By analyzing the cortical activation and functional connectivity of the prefrontal cortex during dual-task obstacle negotiation in older adults,cognitive resources allocation and neural regulatory mechanisms of aging brain were shed light on in complex walking conditions.As a mind-body exercise,long-time Tai Chi practice can improve postural control and effectively prevent falls.However underlying brain mechanism remains unclear.The hemodynamic characteristics of the prefrontal cortex in older adults were compared between before and after Tai Chi practice,and the prefrontal mechanism in improving postural control by Tai Chi was explored.Methods:Study 1:28 healthy right-handed older adults participated in the study,age 65years and older,including 15 men and 13 women.There were four test tasks:Normal Walk（NW）,Obstacle Negotiation during Normal Walk（NW+ON）,Walk while performing Cognitive Task（WCT）,and Obstacle Negotiation during Walk while performing Cognitive Task（WCT+ON）.Participants wore functional near-infrared spectroscopy（f NIRS）to collect hemodynamic signals from 6 regions of interest（ROIs）in the PFC,while the three-dimensional motion capture system and three-dimensional force plate were jointly used to collect the kinematic and kinetic data.Cognitive task data was recorded.Study 2:28 healthy older adults without Tai Chi experience were divided randomly into Tai Chi group and Control group.Tai Chi intervention was conducted four times per week for 16 weeks.The subjects in Control group participated in the health education lectures.27 participants remained and completed the experiment.Obstacle Negotiation during Normal Walk（NW+ON）and Obstacle Negotiation during Walk while performing Cognitive Task（WCT+ON）were performed pre-and post-intervention.The f NIRS,three-dimensional motion capture system and three-dimensional force plate were jointly used to collect the hemodynamic,kinematic and kinetic data.Cognitive task data was recorded.Results:In WCT+ON,the HbO₂ concentration change value（△HbO₂）of the left dorsolateral prefrontal cortex（BA46）was significantly greater than that in the other three tasks（p<0.05）,and the△HbO₂ of the right dorsolateral prefrontal cortex was significantly greater than that in WCT（p<0.05）.The gait velocities in the four tasks significantly dercreased（p<0.05）（NW>WCT>NW+ON>WCT+ON）,COP-COM_ml of the supporting leg significantly increased（p<0.05）,and the difficulties of postural control gradually increased.There was no significant difference in cognitive performance between in WCT and WCT+ON（p>0.05）.In WCT+ON,the left and right dorsolateral prefrontal cortex had strong functional connectivity and the left frontopolar cortex was most widely connected to the other ROIs.Compared to that in NW,the functional connectivity of the left prefrontal cortex was significantly enhanced in WCT+ON（p<0.05）.After intervention in Tai Chi group under WCT+ON,theΔHbO₂ in the frontopolar cortex BA10 was significantly greater（Right BA10P=0.002,Left BA10P=0.001）,gait velocity was significantly faster（P=0.040）,and dual-task cost was significantly lower than pre-intervenion（P=0.047）.TheΔHbO₂ in BA10 under WCT+ON was negatively correlated with dual-task cost（Right BA10r=-0.443,P=0.021,Left BA10r=-0.448,P=0.019）.After intervention in Tai Chi group under WCT+ON,the medial-lateral displacements of the center of pressure（COP）of both legs were significantly lower than those before the intervention（supporting leg P<0.001,crossing leg P=0.012）,and the anterior-posterior displacements were significantly lower than those before the intervention（supporting leg P=0.018,crossing leg P=0.045）.The medial-lateral COP velocities of both legs were significantly lower than those before the intervention（supporting leg P<0.001,crossing leg P=0.012）,and there was no significant difference in the anterior-posterior COP velocities（P>0.05）.Only theΔHbO₂ in right BA10 were in moderately negative correlation with the medial-lateral COP displacements and velocity of the supporting leg（displacement r=-0.507,P=0.027,velocity r=-0.435,P=0.037）.Conclusions:（1）As walking difficulty increased,the PFC activation in the older adults changed from right-sided to bilateral activation,mainly in BA46 of the dorsolateral prefrontal cortex,indicating that the left PFC was activated to compensate for the cognitive resource deficits.（2）The PFC had enhanced functional connectivity in the older adults during dual-task obstacle negotiation,and the cognitive resources recruitment might be achieved by synchronization and coordination of associated brain areas in the PFC.（3）After Tai Chi practice,the bilateral BA10s of the frontopolar cortex were activated to increase the cognitive resources in the older adults,and the functional conpensation of the PFC was enhanced.（4）After Tai Chi practice,the dynamic postural balace in the older adults during the single-task and dural-task obstacle negotiations was improved and the correlations between the PFC and lateral postural control were presumedly increased.