Neurophysiology Mechanism Of Post-traumatic Stress Reaction In Earthquake-exposed Survivors

Post-traumatic stress reaction is different from post-traumatic stress disorder. PTSD is a kind of psychological disorder or symptom after suffering traumatic event. However, post-traumatic stress reaction is commonly found in traumatic individuals, which is reasonable result of traumatic event, rather than a kind of psychological disorder or symptom. Although most of individuals will have different symptoms after experiencing traumatic event, only few of them eventually become PTSD patients. In term of the Wenchuan earthquake had a prevalent impact, huge amounts of people have presented post-traumatic stress reactions.In the most of previous studies, PTSD patients were selected as subjects to explore the influence of traumatic experience on their cognitive neural mechanisms. However, there were few studies to concern the non-clinical survivors who had not presented PTSD symptoms from the viewpoint of prevention and development. Besides, in the field of cognitive neuroscience research, most studies were limited to explore the activated brain regions of PTSD patients. However, there were few studies on cognitive temporal processing characteristic of earthquake-exposed survivors using event related potentials technology (ERP). Based on our previous questionnaire surveys, the current study explored the cognitive processing of the earthquake-exposed group to threat stimuli without PTSD using ERP experiment technology after two years of the Wenchuan earthquake.The dissertation totally included7studies and19experiments. We compared the neurophysiology mechanism of post-traumatic stress reaction (attention, memory and emotion processing) from two dimensions. One was the different degree of earthquake exposure (exposed group and non-exposed group), and the other was different age group (high school student and college student).(1) The neurophysiology mechanism of post-traumatic stress reaction of groups in different degree of earthquake exposure (exposed group and non-exposed group).The first part (including Study1,2and3) was a series of ERP studies on attention bias to threat in earthquake-exposed survivors. Study1investigated the space distribution features of attention resources to threat in earthquake-exposed survivors using a cue-target paradigm. The behavioral and P3latency and peak effect indicated that high school students were more vigilance for cue words in the earthquake-exposed group compared with in the non-exposed group. Meanwhile, the behavioral and Nl peak effect indicated that college students were more avoidant to threat cue words in the earthquake-exposed group compared with in the non-exposed group. However, Study1did not find the difference of attention bias between threat and neutral cue words. It may be related to the time interval of cues and targets.Therefore, Study1tested attention orienting and engagement by supraliminal threat cues, but Study2investigated attention shift by subliminal threat using masked version of the dot probe task. The earlier N1, P1and P2latencies and peaks within valid and invalid trials showed that earthquake-exposed high school students were more vigilance for threat than non-exposed high school students. Even though Study1and Study2tested the attention bias to threat within the theoretical framework of components of attention orienting, it was still unclear that whether there were same cognitive processing characteristics to neutral stimuli in earthquake-exposed survivors. So we did Study3to test it.Study3found that neutral target elicited significantly more reduced P1and P300for earthquake-exposed high school students compared with for non-exposed high school students in posterior scalp using a classic oddball paradigm. It speculated that earthquake-exposed high school students might have attention processing deficits, which was consistent with clinical PTSD symptoms. Although PTSD patients have the disability to focus, a mild traumatic stimulation can induce invasive memory and the phenomenon of flashbacks. Therefore, Study4examined the memory bias to threat in earthquake-exposed survivors.The second part (Study4) was an ERP study on memory bias to threat in earthquake-exposed survivors. Study4found that earthquake pictures elicited longer reaction time, higher accuracy and greater P3and LPC amplitudes effect compared with neutral pictures in earthquake-exposed group using an old/new recognition study-test task. The results on negative stimulation bias can explain the reason of earthquake pictures had enhanced effect compared with neutral pictures. In addition, in terms of Brewin's "duel representation theory" and "neurocognitive model of memory and imagery", it assumed that closely related personal traumatic experiences might be important in the neural mechanisms of episodic memory processing, which produced vivid pictures when recalling disaster scene, i.e."flashbulb memory". However, there was another explain that traumatic experiences might influenced emotional memory of the earthquake-exposed group. Because some study has showed that memory disorders of PTSD patients can't really reflect memory impairment; instead, it is the risk hint of emotional disorders. According to the "multiple memory systems view", there are many brain memory systems with different structure and function. The initial graphical representation existing in the memory system is activated by the priming effect. How did these kinds of episodic memory or emotional memory store in memory systems, and work on cognitive processing? Therefore, Study5and Study6examined the impact of threat priming effect on emotional processing in earthquake-exposed survivors.The third part (Study5and Study6) was on the impact of threat priming effect on emotional processing in earthquake-exposed survivors. Study5used the supraliminal emotional priming paradigm. The behavioral and ERP results revealed that the priming effect is not significant. It may be related to the time interval of priming and target stimuli, i.e. stimulus onset asynchrony (SOA). Because some research found that only a short SOA could lead to priming effect. In order to test the impact of subliminal priming, i.e. unconscious emotional priming, Study6used the subliminal emotional priming experiment paradigm. The results indicated that earthquake-exposed high school students had shorter reaction times to fearful faces and longer to happy faces than to neutral faces followed treat priming stimuli. Meanwhile, both earthquake-exposed high school students and college students had shorter reaction times to fearful faces than the non-exposed group followed treat priming stimuli, with significant N1, P1, P2and LPC effect to fearful faces. Obviously, the earthquake-exposed groups were more sensitive to fearful faces after the treat stimuli priming. However, could we change their emotional function with some cognitive and neural physiological training? Study7did this. The fourth part (Study7) was the research on neural plasticity of cognitive and brain function repair in earthquake-exposed survivors. From Study5and Study6, traumatic experiences influenced the emotional function of earthquake-exposed survivors, and enhanced the sensitivity to negative emotions. Thus, Study7developed an exploratory research on application of the principle of neural plasticity in brain function repair, which took the biofeedback training to adjust anxiety in earthquake-exposed survivors as an example. The results showed that the biofeedback training could effectively relieve negative emotion of earthquake-exposed survivors. It proved that the neural plasticity have effect on cognition and brain function repair through the brain electrical index, which also provided the foundation and possibility through physical intervention and treatment to change psychological and behavioral problems of earthquake-exposed survivors.(2) The neurophysiology mechanism of post-traumatic stress reaction in different age of earthquake-exposed survivors (high school students and college students).The research on Post-traumatic stress disorder suggested that the age was a very important risk factor. Especially the younger, they are more prone to PTSD. Therefore, the current research compared the neurophysiology mechanism of attention bias, memory bias, emotional cognitive processing in different age groups. In Study1and Study2, the results of behavior and an early P1component revealed that earthquake-exposed high school students were more vigilance for threat than earthquake-exposed college students. In Study3, neutral target stimuli elicited smaller P300amplitude in earthquake-exposed high school students compared with earthquake-exposed college students. In Study4, old earthquake stimuli elicited an earlier P3latency and enhanced P3and LPC amplitudes in earthquake-exposed high school students compared with in earthquake-exposed college students. In Study5and Study6, the behavioral and ERP (N1and P1components) results showed that the threat priming effect had greater impact on the emotional processing of high school students than on college students. Particularly, earthquake-exposed high school students were more sensitive to emotion than earthquake-exposed college students, especially for the negative emotion. The results suggested that the traumatic experiences had greater influence for earthquake-exposed high school students, which may be attributed to the brain and cognitive development of high school students.According to all of the studies above, we found that earthquake-exposed survivors' mental and behavioral activities were based on cooperating with all parts of brain. Thus, we finally constructed the Post-Traumatic Stress Reaction Cooperation Cognitive Model (PTSR-CCM) based on the cognitive processing to earthquake treat stimuli in earthquake-exposed survivors. PTSR-CCM is the model of representing cognitive processing characteristics to earthquake treat stimuli in earthquake-exposed survivors. It includes three modules and a principle:attention function, memory function, emotion processing function, and neural plasticity, which revealed the threat stimuli effect on neurophysiology mechanism of post-traumatic stress reaction in the non-clinical earthquake-exposed survivors.