| BackgroundIn recent years,the research of type 2 diabetes mellitus(T2DM)causing central nervous system(CNS)dysfunction,especially the research of cognitive impairment,has been widely concerned.The early cognitive impairment of T2DM patients is not only reflected in memory impairment,but also in attention impairment.Attention is one of the main components of human cognitive function,an important regulatory mechanism of human psychological activities,which is closely related to the information processing process of human cognitive activities.The maintenance,distribution and conversion of attention determine the efficiency of the brain from receiving external stimulation to processing useful information.Based on the theory by Posner et al,attention is an independent network system,which is composed of three parts:alert,orientation and executive control.These three parts are respectively related to different anatomical parts of the brain,neurotransmitters and gene markers.The traditional assessment of attention function is mainly based on neuropsychological scale,which has the advantages of convenience and comparison.The disadvantages are that the paper and pen questionnaire is usually used to study the overall attention function,but the basic components of attention function cannot be analyzed systematically.Recently,Fan et al.designed attention network test(ANT)according to Posner's attention theory,which can effectively test and evaluate the three functions of alert,orientation and executive control of the attention network.The test is simple,time-consuming and easy to be accepted by the subjects and has been widely accepted to be an important technical means and scheme to study and measure the attention function.The present study will explore the changes and related characteristics of attention network in T2DM patients.In addition to ANT paradigm,visual search is also an important method to study attention processing.In visual search,attention plays an important role,which is the internal driving force of visual search.Visual search paradigm has good ecological validity,with a situation simulation of our daily life,which can more accurately distinguish the initial orientation and stay stage of attention function.Facial expression search task(visual search for emotional faces)originates from the visual search task.It presents a series of expression picture matrix to the subjects to search the target expression from the interference stimulus.It is an experience-based,task-driven,top-down and conscious process of attention selection and differentiation of expression information.Facial expression search usually shows the advantage of negative expression search,that is,negative attentional bias.T2DM can affect cognition and attention,but whether it affects facial expression search and attentional bias has not been reported The purpose of this study is to investigate the attention preference of T2DM patients by using the expression search task(searching positive or negative emotional expressions in the neutral expression matrix)Objective1.Neuropsychological questionare was used to evaluate the attention function of T2DM patients.2.Attention network test(ANT)was used to investigate the efficiency of three attention networks,alerting,orientation and executive control network in T2DM patients.3.Using expression search task to explore the attentional bias and expression search mechanism in T2DM patients.MethodParticipantsThirty T2DM patients were right-handed and 40-55 years old,without acute metabolic complications or severe hypoglycemia.The education level was from junior high school graduation(8 years education)to university graduation(15 years education).30 aged-matched healthy controls were selected as the control group.Experimental designCognitive and attentional basic function.Hamilton Depression Scale(HAMD)and Hamilton Anxiety Scale(HAMA)were used to evaluate mental state;MMSE and MOCA were used to evaluate general cognitive function;DST,SDMT,and Trail Making Test A and B were used to evaluate the attentional function.ANT.The ANT test plan proposed by Fan et al.(2002)is adopted.The visual stimulus consists of 5 horizontally arranged black line segments or arrows,where the arrows point to the left or right.The arrow at the center of the 5 arrows or line segments is the target stimulus.The arrangement of stimulus materials includes the following three situations:1)Congruent condition.There are two arrows on each side of the target stimulus,which are in the same direction as the target stimulus arrow;2)Incongruent condition.There are two arrows on both sides of the target stimulus,which are opposite to the direction of the target stimulus arrow;3)Neutral condition.There are two line segments without arrows on each side of the target stimulus.The horizontal viewing angle of a single arrow or line segment is 0.55,and the viewing angle of adjacent arrows or line segments is 0.060 apart.The horizontal viewing angle formed by 5 horizontally arranged line segments or arrows is 3.08°.For each trial,a "+" is first displayed in the center of the screen.After a random stimulation interval(SOA)of 400-1600 milliseconds,a cue"*" appears for 100 milliseconds.Cue are divided into 4 situations:1)no cue;2)center cue."*" appears in the center of the screen;3)Double cue."*" appears above and below the gaze point "+" at the same time;4)Spatial cue."+" appears above or below the gaze point"+" The clues indicate that 400 milliseconds after the stimulus disappears,the target stimulus appears,and the target stimulus disappears after the subject responds to the keys.If the subject does not respond to keystrokes within 1700 milliseconds,the target stimulus disappears directly.After the target stimulus disappears,only "+"appears in the center of the screen for 3500 milliseconds,and then enter the next trial.The subjects were asked to press the left and right mouse buttons as quickly as possible to identify the direction of the central arrow(left or right).The experiment consists of three blocks,each block has 96 trials and lasts about 8 minutes.Take a short break between blocks.Before the formal experiment,practice 12 trials.Visual search for facial expressions.The facial expressions(positive,neutral and negative)were sketch face pictures,in which the distance between the shape of face contour and facial features in each facial image template is different.We created search arrays of five different item sizes(1,2,4,8 and 16 items).The targets were 36 positive faces and 36 negative faces,while the distracters were 36 neutral faces.Different targets and distracters were randomly selected from these pools in each trial.At each set-size,the face pictures were shown on a white screen,at a random position on a virtual 4 × 4 grid(except for set size 16 where all positions were occupied)?Each set size was repeated in 36 trials,half in the target present trials and half in the target absent condition.The order of two target-race blocks,that is,searching positive faces or negative faces among neutral faces,was counterbalanced across subjects.Each trial began with a fixation-cross which appeared at the center of the screen.Subjects were asked to fixate the fixation cross before the trials began,but they were free to make eye movements during the search.They were instructed to report as accurately and as quickly as possible whether the display contained a target or not.The search array remained on the screen until the subject made a response by means of the keyboard.The response key was counterbalanced across subjects.A new trial began automatically 1000 ms after the response and a tone provided negative feedback after errors.ResultCognitive and attentional basic function test.The score of MoCA in the T2DM group was significantly lower than that in the normal control group,showing overall cognitive impairment including attention,visual space,language,abstraction,and delayed memory,especially the attention test items,indicating that the attention function of diabetic patients was more serious than that of the normal group.In the assessment of attention function,the scores of DST(reverse)and SDMT in the T2DM group were significantly lower than those in the normal control group,suggesting that T2DM patients have serious obstacles of attention coding function,visual perception and attention persistence function;in the connection test,the score of TMT-B in the T2DM group was significantly higher than that in the control group,indicating that the T2DM group has reduced flexibility in attention and executive functionsANT.The ANT showed that the response time of T2DM patients to conflict condition was significantly longer than that of the normal control group,indicating that the executive control efficiency of T2DM patients was lower.There was no significant difference in the efficiency of alert network and directional network.Pearson correlation analysis showed that the efficiency of executive control was negatively correlated with the course of disease,BMI index,HbAlc and advanced glycation end products.Visual search for facial expressions.Both groups showed serial and self-terminating expression search,with faster and higher accuracy for negative expression search,i.e.,negative attentional bias.In the normal group,there was no significant interaction of target stimulus type(absence and presence)and expression features(positive and negative),indicating that the search advantage for negative expression depended not only on the rapid recognition of target stimulus,but also on the rapid rejection of distractor items.Compared with the control group,T2DM patients have lower accuracy of expression search,longer response time,and more modulation by the number of items(i.e.,higher search slope),indicating that T2DM patients have serious expression recognition and search dysfunction.The significant interaction effect of target stimulus type(absence and presence)and expression features(positive and negative)indicates that the expression search disorder in T2DM patients is mainly caused by the slower inhibition speed of distractors(especially the inhibition speed of positive expression).Conclusion1.In T2DM group,there are significant cognitive impairment,mainly in attention,visual space,language,abstraction,delayed memory,and so on.The attention function of T2DM patients is more seriously damaged than that of normal people,especially in coding function,continuous function and executive function.2.For ANT test of attentional network,T2DM patients have a significant reduction in the efficiency of executive control network,but the efficiency of alert network and directional network is relatively normal.The efficiency of executive control was negatively correlated with the course of disease,BMI index,HbAlc and advanced glycation end products.3.T2DM patients have serious expression recognition and search impairment,which are mainly caused by the slower inhibition speed to distractors(especially the inhibition speed of positive expression),which further indicates that T2DM patients have attention function defecits of conflict inhibition. |
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