Impairment Of Vigilant Attention In Insomniacs And Its Neural Mechanism

Sleep is essential for individuals to maintain normal physiological and psychological functions,and people spend about a third of their time on sleep each day.However,as a consequence of fast pace and high pressure of modern life,insomnia has become a common clinical sleep disorders,and about 27% number of people are suffering from it according to the investigation of the World Health Organization(WHO),while the morbidity as high as 38.2% in China.Insomnia refers to a subjective feeling about that individuals are not satisfied with sleep time and/or quality of sleep,and which also affects the daily function despite they have appropriate sleep opportunities and sleep environment.Insomniacs often have trouble in falling asleep and maintaining sleep,with sleep time reducing,awakening more often at night and waking up earlier than desired.At the same time,insomnia impairs their mental function,such as reaction time,attention,vigilance,memory,decision making,executive function and emotional disorder etc.Vigilant attention refers to that individuals keep detecting and persisting ready for the adaptive stimuli which may or may not appear.It's very susceptible to sleep loss.The Psychomotor Vigilance Test(PVT)is a common paradigm for measuring the individuals' vigilant attention after sleep deprivation(SD),and numbers of researches have indicated that the performance of PVT was decreased,including prolonging of reaction time,declining of reaction rate and increasing of rate of lapses(RT>500ms)after sleep deprivation.However,the processes of insomnia and sleep deprivation are different,and now we lack the certain evidence of researches on whether there is significant impairment of function of vigilant attention in patients with insomnia.In addition,there is no research to explore the neural mechanism of vigilant attention in insomniacs.Thus,to investigate whether there is impairment of vigilant attention in insomniacs and its neural mechanism,we carried out the following two experimental studies.Study 1 used the behavior method to investigate the difference between the normal sleepers and insomniacs on the performance of PVT.Thirty-one patients with insomnia were screened clinically,and 32 normal sleepers with age,gender and education-matched were selected as the control group.All subjects completed five minutes of PVT from 2 p.m.to 5 p.m.,and we also collected all subjects' sleep,mood,thinking control ability and personality questionnaires.Compared with the normal sleepers,insomniacs showed the significantly increased RT of PVT,the lower reaction rate and the significantly increased rate of lapses.In addition,the analysis of questionnaires showed that the PSQI of insomniacs was significantly increased,the sleep latency time was significantly prolonged,and SDS and SAS scores were increased significantly.In addition,we found that RT of PVT and Positive Affect was significantly associated in the insomnia group according to the correlation analysis.So,results suggested that insomniacs showed impaired function of vigilant attention,which is influenced by the emotional disorders.Although the behavioral study have shown that patients with insomnia showed impaired function of vigilant attention,the neural mechanism of the injury is not clear.In study 2,we aimed to reveal the neural mechanism of the impaired function of vigilant attention in patients with insomnia by the resting-state fMRI.Resting state is a condition that brain neurons activate spontaneously when individuals keep awake,relaxed.Resting-state fMRI is a noninvasive technology to study the baseline of brain activity and has been applied in the researches about heathy people and psychiatric patients.The abnormal brain activity in insomniacs and function connectivity may reveal the pathogenesis and change of cognition and emotion of patients,which can help improve diagnosis and treatment for insomnia.We collected the resting-state fMRI data of 31 insomniacs and 32 healthy sleepers and mainly analysed the difference of amplitude of low frequency fluctuation(ALFF),the fractional amplitude of low-frequency fluctuations(fALFF),the FC of ROIs and the FC of large-scale brain networks between two groups.What's more,we analysed the correlation between the ALFF,fALFF and FC and the performance of PVT,sleep,emotion and thought control ability scores in the group of insomniacs.We found that,compared with normal sleepers,(1)insomniacs showed significantly decreased ALFF in the left insula,left supramarginal and left postecentral gyrus(LPCG),and increased ALFF in the left posterior cingulate(PCC),left precuneus and left superior temporal gyrus(LSTG);(2)Insomniacs showed significantly increased fALFF in paracentral lobule,sub-gyral of parital cortex,LSTG,Brodmann area 5 and Brodmann38;(3)Patients with insomnia exhibited the significantly increased functional connectivity between PCC and precuneus,between paracentral lobule and precuneus,but decreased functional connectivity between paracentral lobule and Brodmann 38;(4)Patients with insomnia showed the significantly increased FC between the frontoparietal control network(FPC)and the dorsal attention network(DAN)and decreased FC between the sensorimotor network(SMN)and auditory network(AN);(5)The ALFF of precuneus was significantly negatively correlated with Sleep Latency Time(SLT)after controlling the effect of age;(6)The FC between insula and precuneus and FC between insula and PCC were significantly associated with the SDS scores;(7)There was a significant correlation between FC of paracentral lobule-Brodmann 38 and RT of PVT.The results of comprehensive study 1 and 2 showed that(1)Patients with insomnia showed emotional disorders and impaired ability of attention and mind control.(2)The abnormality of ALFF in the resting state and the significant correlation with the SLT indicated that the abnormality of ALFF may be the neural mechanism of difficulty in falling asleep in insomniacs.(3)The significant correlation between the FC of ROIs and the emotional scores as well as performance of PVT may suggest that the abnormality of functional connectivity is the neural mechanism of the emotional disturbance and impairment of vigilant attention in patients with insomnia.