Overgenerality Of Autobiographical Memory And FMRI In Young Depressed Individuals

Depression is one of the most important and commonly occurred mental disorders.WTO predicted that depression would become the second pathogeny of death and deformity by 2020. In our country, the prevalence rate of depression is very serious. The average prevalence age of depression was 25 years old, most occurring in individuals at 15-19 years old and 25-29 years old, among which, about 10%-15% had suicidal risk. An international survey on September 8th in 2007 showed that depressive disorder had more serious effects on human beings than angina, arthritis, asthma and diabetes. These researches hint that depressive disorder is an important public health problem needing immediate attention.Many researchers paid more attention to the developing mechanism of depression in the angles of cognitive psychology, social psychology, neurobiology, psychological immunity, genetic gene, and so on. On the study of cognitive mechanism of depression, most researchers found that depressed individuals had negative and general cognitive schema, inclined to choose negative and general information consistent with the negative emotional state (negative attention processing bias), and recalled more negative information manifesting as negative recall processing bias. Negative processing bias led the negative and general information to be processed more by depressed individuals, which would cause the maintenance and worsening of depression. These results showed that the memory of depressive individuals was one of the important link for depression occurrence and development.Autobiographical memory as a research focus of memory fields is about some past especial situations recalling and it is memory of the personal life events. Autobiographical memory can be divided into specific autobiographical memory and overgeneral autobiographical memory, which has the laete self characteristics and emotional overtone and own neural network. Depressed individuals had plenty of negative emotions and different cognitive models compared with the normal controls. Therefore, the study on autobiographical memory of depressed individuals has great theoretical and practical significance. Many studies found that autobiographical memory was different in the normal and the depressive individuals, and the specific autobiographical memory of depressed individuals was significantly less than the normal controls, and manifested as overgenerality. Then, this difference whether or not resulted in different brain activation patterns? The previous studies found that brain activation patterns of autobiographical memory in normal individuals were the left unilateral brain activation, including hippocampus, prefrontal and temporal lobes, cuneus, medial frontal and posterior cingulates and so on, among which the left prefrontal cortex played an important role in memory retrieve. Specific and overgeneral autobiographical memories have different neural networks. However, we have no knowledge about the brain activation patterns of overgeneral autobiographical memory in depressed individuals.The present study explored the characteristics of autobiographical memory in young depressed individuals with classical AMT task, and the brain activated area and activation patterns of autobiographical memory were analyzed by functional magnetic resonance experiment, and the features of the brain activated area under different autobiographical memory tasks were discussed. It would preliminary illustrate the brain mechanism of overgeneral autobiographical memory in depressed individuals. The following outcomes and conclusions were obtained:1. The scores of the normal were higher than those of the individuals with depressive mood and the depressed, and there existed significant statistical difference between them (P<0.01), and the scores of the depressed were the lowest than the normal and the depressive mood individuals. The scores in memorizing postive cue words were higher significantly than those in memorizing negative cue words in normal individuals (P<0.01), but not in depressive mood individuals and drepressed individuals (P>0.05).2. The scores of individuals with different depressive moods were significantly different (P<0.01): the individuals with mild depressive mood had higher scores than the individuals with moderate and severe depressive moods (P<0.01), but there was no significant difference between the individuals with moderate and severe depressive moods (P>0.05). The autobiographical memories of depressive mood and depressed individuals had specific memory deficits, which were mainly manifested as overgenerality. The overgeneral autobiographical memory was the stable mark and vulnerable factor in depressed individuals.3. The neural networks of autobiographical memory retrieval in the normal individuals were similar to the depressed individuals. But the size of the activated brain area of autobiographical memory retrieval in normal individuals was bigger than that of the depressed individuals, and the strength of the activated brain area of autobiographical memory retrieval in normal individuals was stronger than that of the depressed individuals. The left middle frontal gyrus (BA 9)and the left superior temporal gyrus (BA 39) were the major positions of autobiographical memory retrieval in normal.4. The activated brain area of the normal and the depressed individuals had significant differences under specific autobiographical memory task. The strengths of the activated brain areas such as the left middle temporal gyrus (BA 21), the right fusiform gyrus (BA 37), the left cuneus (BA 18), and the putamen in depressed individuals were weaker than those of the normal. These results suggested that the function of the brain area had deficits in depressed individuals. However, the right superior parietal lobule (BA 7) in depressed individuals was strengther than the normal, which suggested that depressed individual may enhance the ability to inhibit the detail information for emotional stimuli. The above brain area may have a relationship with memory retrieval bias or the overgenerality characteristics of autoiographical memory in depressed individuals.5. The activated brain area of the normal and the depressed individuals had significant differences under overgeneraly autobiographical memory task. The strengths of the activated areas such as the left cingulate gyrus (BA 31), the left middle temporal gyrus (BA 19), and the left superior occipital gyrus (BA 19) in depressed individuals were weaker than those of the normal, which showed that depressed individuals may have a defect in retrievaling the detail information and who suffered from interfering for unimportant information, but the right insula (BA 13) in depressed individuals was strengther than the that of the normal, which showed that depressed individuals had paid more attention to the negative cognition and negative emotional events. So the above brain area may be related to the deficient of the executive control in depressed individuals, and more deficient of the executive control was, more overgeneral autobiographical memories had in depressed individuals.6. The activated brain area, activated intensity and activated size of the specific and overgeneral autobiographical memory retrieval in normal individuals had significant differences. Specific autobiographical memory could mainly activate bilateral brain area, and overgeneral autobiographical memory could mainly activate the left brain area. The activated intensity of specific autobiographical memory was higher than that of the overgeneral autobiographical memory in bilateral cingulate gyrus, bilateral superior temporal gyrus, bilateral middle temporal gyrus, left cerebellum and thalamus.7. The brain area of specific autobiographical memory was similar to the overgeneral autobiographical memory in depression. The activated intensity and activated size of the above memory tasks had no significant difference.In the present study, we observed the autobiographical memory retrieval characteristics in depressed individuals and the brain area activated characteristics under different autobiographical memory tasks. On one hand, the present study has developed the contents of cognitive processing in depressed individuals, deepened the theory research of cognitive bias in depression, which will be beneficial for understanding the development of depression, on the other hand, it has explained neurological physiological mechanism of depressed individuals, and it will offer theoretical basis for cognition and clinical treatment for depressed individuals.