| Objective: According to the findings from neuropsychological studies, prosopagnosia patients could not recognize familiar faces but they could retain the capacity of discern facial expression. The fact prompt dissociation between face identity and facial expression processing. Yin reported the inversion effect of face, which means recognition accuracy for inverted faces decline and the reaction time prolong. Bruce and Young put forward the cognition model of face recognition, which emphasize parallel processing of facial information such as identity and facial expression. Using fMRI, facial identity processing was located in the right fusiform gyrus.Haxby proposed that the neural network model of face processing consist core and extend system,and separately involved in visual frame analysis,spatial attention,emotion,identity and name.In which facial expression processing involved in the limbic lobe.The neuroanatomical structure of emotion processing consisit of orbit-frontal cortex,hippocampus,cingulated gyrus and amygdale.The definition of emotion is people's attitude ,experience and reaction to objective things.Adopt different facial expression(positive,negative and neutral)picture to evoke emotion is normal kind of study pattern,ERP could provide high distinguished time information. During face recognition processing studies, Bentin first report a negative waveform whose latency was about 170ms in temporo-occipital area selectively responsive to face identity cognition (structure analysis),which reflected the early structure encoding stage and was not related to face familiarity, sexuality, age and race. Theinverted face could delay the latency of N170 and enlarge the amplitude. Adobe deep electrode in ventral temporo-occipital cortex before an operation of epilepsy patients also have recorded N200, which related to face recognition. Most of studies in face processing concentrated in the latency and amplitude of N170 or N200, not involved in the ERP components change of the other area and stage. During the depression cognition processing studies, find that the depression patients had negative deviation in attributional styles, negative self schema, automatic thoughts and negative ways of tackle. There were significant evidence of difference between depression patients and normal from Neuropsychological, biological, neurological image and functional image studies. The research from ERP showed that amplitude of P300 related to auditory sense in depression patients group was lower than control group. The latency and amplitude change of inner resource component of N2 and P3 show that there was fairly serious cognition abnormal in depression patients . The latency and amplitude change of outer resource component of Nl and P2 show that there was fairly serious cognition abnormal as well as alert, select and attention disorder in depression patients. Research prompt that there maybe abnormality in the predominant hemisphere and the right cerebral hemisphere (modulation of complicated tone processing) of the depression patients with somatic anhedonia. Previous research usually limited in the analysis of few ERP components. Most scholar which study the ERP of depression patients only observed the ERP which related to auditory stimuli (P300). This study adopt Time-space pattern analyze: (1) Time-space pattern features of event-related potentials (ERP) induced by facial processing expression effect and direction effect of healthy middle and old aged people; (2)The difference of "emotion wave" between the the depression patients after stroke and healthy middle and old aged people,probe brain mechanism of facial processing and clinical evaluation to emotion ERP by depression after stroke; (3) clinical research on emotion ERP of depression patients sufferers after stroke has not been reported nationally now.Methods: 28 control group subjects(mail 16,femail 12)all are workers or retired workers or family members of Southern Medical University,2 female subjects and 1 male subject are rejected because of too much disturbness of brain wave. Datas from25 healthy subjects are analyzed.age from 37 to 79,average age 51.62 ± 11.69.voluntary participation the experiment,now and then have no mental disease.Recruitment criteria: all of the cases had first-time onset of stroke with no history of organic cerebral lesions and the brain scanning found single lesion on left side. In order to exclude the influence by conscious, recruitments were permitted at least 14 days after acute onset of stroke till the subject was regain consciousness, able to stand and sit, being right-handed, being capable of cooperation, normal ability of direction, no obvious memory retention disorder and intelligence incapacity. All of the subjects were performed high-rate brain function screening to exclude those with dementia. The manifestations were in line with the diagnosis standards for depression after stroke and depression should be moderate or more severe by evaluation with Self-Rating Depression Scale. The subjects should have normal vision or corrected normal vision. And the subjects should be able to concentrate for cooperation during the assessing period.Three categories of stimuli were used: positive, neutral and negative emotional schematic face pictures. The corresponding inverted stimuli and three Chinese words (happy, think, fear) were also presented. Thus, these nine pictures were viewed fifty times in the total of four hundred and fifty picture presentations. The pictures were displayed separated for 1.5 second each and presented in random. Inter-trial intervals was 1500 ms. Subject's task was to press a key if the successive stimulus was the same. Subjects were instructed to respond as accurately and as quickly as possible. All responses were made with the right hand. Participants were seated in a dimly lit sound attenuated cabin, with response buttons under their left and right hands, at 100 cm from a computer screen (resolution, 800 x 600 pixels, vertical refresh rate, 85 Hz). The size of pictures presented in the center of the screen is 10.6 x 12.3 cm2 with visual angle 6.0 x 7.0°. The total trial was made of five blocks each of which would take 135 seconds. Subjects could have a rest for thirty seconds between the successive block. Before Event-related EEG was recorded, subjects had a short training block of 20 stimuli. Event-related EEG was recorded from 19 channels of international 10-20 system (see Fig. 2) with linked earlobes as reference. EEG was amplified by means of a ERP system developed in our lab,digitized with samphng frequency of 1000 Hz and bandwidth of (0.10, 30) Hz and 50 Hz notch. Electrode impedance during the experiments did not exceed 5 k￡X EEG epochs from 100 ms before to 1000 ms after target stimulus (see Fig. 1) were averaged. Trials contaminated with ocular, muscular or any other type of artifacts were inspected visually and rejected. Sweeps exceeding ± 50 microvolt in any channels and those with incorrect performance were excluded from the ERP averaging offline. ERP waveform elicited by the different (facial expression, orientation) pictures and accuracy would be statistic analyzed. In control group, the 3(expression: positive, neutral and negative) X 2(orientation: upright, inverted) factorial design of repeated-measures was applied with statistical parametric mapping (SPM) of F-value. In the contrast between depression and control, the group t-test was applied to their "emotion-wave" (EP), which was subtracted from emotional (positive, negative) wave to neutral wave, SDS scales, response time and accuracy. The t-value of "emotional wave" was presented with statistical parametric mapping.Results: Six waveforms had been elicited in control group. Name after their amplitude polarity and ridge,they were Nl^ P140> P200x N200, N260^ P260 . P370n N55O separately. On every test condition,we can see the composition of the ERP distributed on the scalp: N140> P2^ N260 according to the anterior and central region of head; P140n N200> P260 according to posterior region of head; anterior and central region N140-P200-N260 and posterior region P140-N200-P260 these two "compound wave" are opposite in polarity, P370 according to the anterior and central region, N550 distribute to the posterior region of head, statistical parametric mapping (SPM) of F-value shows there is significant mutual-effect of expression and orientation appeared in the left parietolis region(280-295ms) and left parieto-occipitalis-temporal region(415-445ms); Significant main effect of expression appeared in the right temporal region(75-90ms), left occipitalis-temporal region(85-100ms),bilateral occipitalis region(310-340ms), bilateral frontal-parieto region(445-490ms). Significant main effect of orientation appeared in the bilateral occipitalis- parieto region(85-105 ms), bilateral frontal-parietal-occipitalis region(190-220ms), bilateral frontal-parieto region(250-340ms), right frontal-parietoand bilateral occipitalis region(400-445ms).Statistical parametric mapping (SPM) of t-value shows (positive-neutral) that the significant main effect of expression appeared in the left occipitalis-temporal region(120-160ms),bilateral frontal-parieto region(220-240,320-340ms), right occipitalis-temporal region(480-520ms).compare the group of depression after stroke and control group: SDS scale of depression group was 55.80±6.32, SDS scale of control group was 36.47 ± 8.63,there are significant difference between the two groups(t=7.35,p<0.05). response time and accuracy elicited by the different (facial expression, orientation) pictures of the group of depression after stroke been done statistical of factorial design of repeated-measures and ANOVA test,, response time and accuracy have no significant difference between every group,( p<0.05), response time of the group of depression after stroke recognition the pictures is longer than the control group,(889.04±46. 37) vs (697. 48 + 86. 95) ms, t=6. 85, p<0. 05; accuracy is lower (84.35 ± 18.97)%vs(90.86 + 5. 32)%, t=l. 59, p<0. 05. ERP spatiotemporal Patterns of 11 patients show the composition of the ERP distributed on the scalp: N150> P210 according to the anterior and central region of head;N270 according to the right region of head,P390 which is lower in amplitude distribute to wide range region of the head symmetry by vertex. Significant effect of differenct expression wave(positive-neutral)between the patients group and normal group appeared in the left occipitalis-parietal- temporal region( 170-190ms), bilateral frontal-parieto region(170-230ms), bilateral frontal-parieto region(370-430ms), wide range region of bilateral scalp(480-550ms).DISCUSSION: The results indicated that depression sufferers after onset of stroke had abnormal ERP induced by emotional face identification, suggesting that facial expression identification makes for social activities, environment adaptation and mental adjustment in the social life of human being. The results attract people's attention on health and disease rehabilitation and the research provides an exploring model for neural mechanism of emotional activities from perspective of electrophysiology and provides electrophysiologicai data for clinical diagnosis and treatment.Conclusions: The definition of emotion is people's attitude .experience andreaction to objective things. ERP spatiotemporal patterns can reflect the process of emotion in the brain sensitively,can pride electrophysiology research pattern of neural mechanical study and clinical apply for emotion activity.
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