A Behavioral And FNIRS Study On The Improvement On Attention Of Military College Students By Repeated HD-tDCS

Background:Modern war environment shows unprecedented complexity and variability,which poses a great challenge to the cognitive ability of soldiers.The tremendous amount of data,images,language and other information generated in military missions such as long-term surveillance and reconnaissance under the information operation mode is beyond the bearing capacity of the soldier.The complex operation sequence of updated weapons requires better ability of rapid response and multi-task processing of the soldier.Therefore,it is extremely critical for the soldier to maintain an efficient consciousness during battle process,acquire and understand the key information flexibly and accurately,make rapid and continuous response.Attention,as a basic and core cognitive ability,is regarded as the navigator of human cognitive activities,which ensures people’s clear understanding of substance,accurate response and controlled behavior.At present,many fields have put forward higher requirements to the attention of soldiers,such as air traffic control,long-term flight,night battle,rapid response under high alert,etc.The traditional methods for improving attention mainly include task-based attention training and attentional state training.These methods require individuals to pay much effort and time.However,there are new attention enhancement methods,such as t DCS(Transcranial Direct Current Stimulation).The emerging methods for improving attention are mainly characterized by new theories and new technologies,which overcome the problems of classical methods for improving attention.The research uses multiple and long-term HD-t DCS(High-definition Transcranial Direct Current Stimulation)over left DLPFC(Dorsolateral Prefrontal Cortex)to improve attention ability.In addition,to analyze the data of behavior and brain image acquired by serial attention test and fNIRS(Functional Near-Infrared Spectroscopy)can show the change of attention and cortex,and can provide experimental evidence for establishing a scientific,reasonable,convenient,feasible scheme for improving attention.Subjects and methods:This study includes four parts.Healthy college students in military school were randomly divided into stimulation group and control group.The stimulation group received active HD-t DCS,while the control group received sham HD-t DCS.The subjects in the first three parts were identical.A total of 39 subjects received a four-weeks intervention(three times a week).In the fourth part,a total of 43 subjects received 9interventions.All intervention undertaken every other day.In the first part,the tests related to attention networks undertaken before intervention and on the last day of each intervention week.Separate 2(grouping: stimulation group,control group)× 5(time: baseline,week 1,week 2,week 3 and week 4)repeated measures ANOVA tested for group differences in each task over time,which includes attention network test consisted of three sub-networks and CW-Stroop test.We aim to explore the variation tendency of attention network by repeated HD-t DCS.In the second part,the tests related to attentional characteristics were performed before intervention and on the last day of each intervention week.Separate 2(grouping:stimulation,control group)× 5(time: baseline,week 1,week 2,week 3 and week 4)repeated measures ANOVA tested for group differences in each task over time,which includes attention stability test,attention span test,attention distribution test and attention shift test.We aim to explore the variation tendency of attention characteristics by repeated HD-t DCS.In the third part,fNIRS was used as a monitoring tool to evaluate the resting-state functional connectivity of the left and right DLPFC and adjacent brain regions.Single factor(time: before,during and after the experiment)repeated measures ANOVA was used to test for time differences on fNIRS data of two groups.We aim to explore the changes in the resting-state neural mechanisms by repeated HD-t DCS.In the fourth part,fNIRS was used as a monitoring tool to evaluate the blood flow signal of the left and right DLPFC.A 2(grouping: stimulation group,control group)× 2(time: the baseline and after test)repeated measures ANOVA tested for group differences in CW-Stroop test scores and fNIRS data over time.We aim to explore the effect of repeated HD-t DCS on brain hemodynamics under task state.Results:Part Ⅰ:(1)The executive control and the psychomotor ability in the stimulation group were significantly improved compared with that in the control group,but there were no significant changes in the orienting and alerting.(2)Compared with the baseline level,the executive control and psychomotor ability of the stimulation group significantly improved from the week 1 and maintained until the week 4.(3)Compared with the baseline level,the executive control and psychomotor ability of the control group gradually recovered to the initial level in the late intervention period,and there were significant differences between two groups from the week 3(i.e.,after 9 interventions).Part Ⅱ:(1)There was no statistical difference in attention stability between the control group and the stimulation group.(2)In terms of attention distribution,the performance of both the control group and the stimulation group was significantly improved compared with the baseline.However,this change was only affected by the time factor,and the grouping factor had no significant effect on it.(3)In terms of attention shift,the performance of the stimulation group from week 1 to week 4 was significantly improved compared with the baseline,while that of the control group was not significantly changed.After week 3,there were significant differences between the two groups.(4)For attention span,the performance of the stimulation group from week 1 to week 4 was significantly improved compared with the baseline,but there was no significant change in the control group.After week 3,the performance of the control group began to get worse,while the performance of the stimulation group still maintained its previous benefit,and the performance of the stimulation group at week 2 and week 4 was significantly higher than that of the control group.Part Ⅲ:(1)The strength of functional connection of the stimulation group during and after the experiment was significantly decreased compared with that before the experiment;In the control group,functional connection strength changed less during whole experiment.(2)For the proportion of channel connection with significant change in correlation coefficient before Bonferroni adjustment,the stimulation group(29.71%)was much higher than the control group(7.03%);The functional connectivity of the left and right frontal lobes and interhemispheric connection was significantly reduced in the stimulation group,but not in the control group(P value was Bonferroni adjusted).Part Ⅳ:(1)The time main effect of the Stroop effect on the error rate of two groups was significant.The error rate of neutral and consistent conditions in the control group was significantly increased,but there was no significant change on the error rate of the stimulation group.(2)The Stroop effect of bilateral Hb O concentration of DLPFC was decreased in the stimulation group,but not in the control group.(3)The reduction of Stroop effect of HBO concentration was only significant in the right DLPFC.Conclusions:There were behavioral and imaging results in the present study.For behavioral results,repeated HD-t DCS significantly improved the executive control,psychomotor ability,attention shift and attention span.The cumulative effect occurred after about 9 HD-t DCS interventions,which meant there was a significant difference between the stimulatuon group and the control group.For imaging results,the repeated HD-t DCS significantly reduced the strength of functional connection of interhemispheric connection and bilateral DLPFC and adjacent brain regions,which meant repeated HD-t DCS improved the connected efficiency and work efficiency of the cerebral cortex;and activation of bilateral DLPFC under task state were lower,but only the change of the right DLPFC was significant,this results not only supported the rule of interhemispheric cooperation,and also showed same conclusion about the change of functional connection that HD-t DCS promote work efficiency of the cerebral cortex.From the perspective of behavioral and imaging,this study comprehensively discussed the effect of repeated HD-TDCS on the improvement of attention function of military college students,and found the variation rule of attention function and the related neural mechanism,which provided an experimental basis for the actual promotion and application of HD-TDCS in the army.