| Mental fatigue can have a great impact on the body's cognitive,emotional,and behavioral abilities.In severe cases,it can also harm work performance and physical and mental health.With the higher requirements for the modernization of the Air Force equipment and the actualization of combat training,as well as the high load operations in the future battlefield environment and for lack of sleep caused by long-time flight,the risk of mental fatigue for pilots will increase significantly.According to foreign military investigations,93% of pilots had flight fatigue,and 10-54% of all combat casualties were caused by fatigue.Therefore,the mental fatigue and countermeasures of flight personnel are an important research area for aviation medical protection in various countries.This paper is funded by major special projects of the “Twelfth Five-year Plan” and “Thirteenth Five-year Plan” of the military in China.This study builds a mental fatigue medical model under laboratory conditions by means of sleep deprivation.Advanced brain electroencephalogram(EEG)and functional magnetic resonance technology combined with complex network analysis and other front-end data processing methods were used to study how the resting state and task state brain functional network changes after mental fatigue and how mental fatigue affects the intrinsic neural mechanisms of brain emotions and advanced cognitive functions in order to provide reliable biological quantification indicators for the evaluation and early warning of mental fatigue of military flight personnel,and propose a scientific basis for establishing effective protective measures.MethodIn this study,a total of 37 healthy male subjects were recruited,and self-control designs were used to establish a mental fatigue model under laboratory conditions using 40-hour sleep deprivation.At six time points,18 EEG acquisitions were performed for 3 states(eyes open,eyes closed,and flight simulation tasks),2 functional magnetic resonance scans(before and after deprivation),and the participants' cognitive ability and mental and physical states were dynamically monitored.The power spectrum,phase lag index,weighted graph,minimum spanning tree,functional connectivity density,psycho-physiological interactions and correlation analysis and other calculation methods were used to investigate cognitive impacts of mental fatigue on emotional state,attention,risk decision-making,and complex operational capabilities.The impact of the patterns of changes in neural mechanisms such as brain oscillation activity and functional network topology under resting and task states were also analyzed,and the correlations between behavioral performance and neural mechanisms were also investigated.Results1.The impact of mental fatigue on cognitive function,emotion and behaviorPhysical and emotional status assessment questionnaires,psychomotor vigilance test(PVT),game of dice task(GDT),simulated flight tasks and other assessment methods were selected to study the impact of mental fatigue on cognitive function,emotions,and behavioral patterns.The results revealed that among mental fatigue subjects(1)fatigue,sleepiness,and negative emotions were significantly increase;(2)inattention increased and risk decision-making ability was impaired;(3)decreased ability to perform complex operations;(4)the decline in complicated operations occurred first,followed by a decline in emotional,attention,and risk decision-making abilities;(5)negative emotions such as anger and tension were positively correlated with risk decision-making ability and impairment of complex operation ability,and positive emotions such as self and energy were negatively correlated with impaired risk decision-making ability.2.Effect of mental fatigue on resting state brain functional networkBrain functional networks were constructed using resting state EEG data to study the relationships between the characteristics of brain oscillations and the topological structure of brain functional network and its correlation behavioral characteristics.The results showed that in the eye-closed state,(1)the power spectrum of the slow wave increased while the power spectrum of the fast wave decreased,indicating that the brain oscillation activity tended to slow down;(2)the trend of the regularity of the ?-band network and the enhancement of the small-world characteristics of the ?-band network;(3)the global efficiency of ?,?-band network decreased,and the local efficiency of ?-band network decreased;(4)the stability of ?-band network had a slight increase;(5)the betweenness centrality of network of ?-band decreased;(6)the critical backbone of the brain functional network at ?-band brain trunk presented a star-shaped change;(7)the global efficiency and local efficiency of the ?-band network were negatively correlated with changes in fatigue,and positively correlated with self-change,which meaned that with the decrease of global efficiency and local efficiency,the fatigue feeling increased and self-mood decreased;(8)the change of the center frequency of ?-band network was positively correlated with the change of PVT response,suggesting that with the decrease of its centrality,attention decreased.The results showed that in the eye-opened state:(1)the power spectrum of the slow wave increased while the power spectrum of the fast wave decreased,indicating that the brain oscillation activity tended to slow down;(2)the network stability of the ?,?,? bands was slightly increased;(3)The change in cerebral cortical oscillation activity was positively correlated with the PVT response,suggesting that attention decreased as the brain oscillatory activity slowed down.3.Effects of mental fatigue on task-state brain functional networkThe brain functional network was constructed using EEG data under simulated flight mission status to study the relationships between brain oscillatory activity and topological structure of brain functional network and its behavioral characteristics.The results showed that(1)slow wave power spectrum increased,fast wave power spectrum decreased,indicating that the brain oscillation activity tended to slow down;(2)the ?,? band network became more regularized,and the small-world characteristics of the ? and ? band network were enhanced;(3)global efficiency of ? and ?-band networks increased;(4)the centrality of the ? and ?-band network was enhanced;(5)the overall connectivity of the brain backbone network was enhanced;(6)The diameter of the ?-band brain backbone network was larger and the degree of eccentricity was increased;(7)the balance of the backbone network was enhanced at ?-band brain;(8)the change in brain oscillation activity was positively correlated with the PVT response,suggesting that as the brain oscillation activity slowed down,attention decreased;(9)changes in the local efficiency and centrality of the ?-band network were positively correlated with the changes in PVT response,suggesting that attention decreased as the local efficiency and centrality increased;(10)there was a positive correlation between the changes in simulated flight mission performance and changes in the small-world characteristics and global efficiencies of beta-band networks,suggesting that as their small-world characteristics and global efficiencies increased,the performance of simulated missions improved.4.Differences between the resting state and the task-state brain functional networkIn contrast to the two states,it was found that the centrality of the ?-band network decreased in the resting state(eye-closed),and was accompanied by a decrease in attention.The the centrality of the ?-band network is enhanced and the attentional decline is accompanied in the simulated flight mission state.It is suggested that there may be differences in the subcomponents of the ?-band in these two states.ConclusionThis study was closely related to military needs.Combined use of brain electroencephalogram,functional magnetic resonance imaging methods,sophisticated network frontier analysis techniques and multi-dimensional indicators revealed the characteristic changes of brain functional network topology,and these changes are closely related to emotional states,cognitive functions,and complex operational capabilities.It was further found that under brain fatigue resting state,the brain functional network efficiency decreased and the brain oscillation activity began to slow down.These changes were positively correlated with the decline of cognitive function and negative emotional state.Under high-fidelity flight simulation tasks,the small-world characteristics and network efficiency of the ?,? band increased and this change was positively correlated with the performance of complex operation tasks.These research findings can go a long way towards understanding the neural mechanisms by whichbrain fatigue affects the complex networks of the brain,thus facilitating the evaluation and prevention of mental fatigue of military flight personnel during peacetime and wartime. |
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