An Event-related FMRI Study On Task Instructions And Emotional Memory

Background and Objective It is well known that emotionally evocative stimuli are better remembered than neutral stimuli. This phenomenon is called emotional memory enhancement effect. Emotion can modulate memory process, it is exactly why emotional memory enhancement effect happened. There is a common opinion that amygdala plays a critical role in memory consolidation by modulating other related cerebral regions. However, there are some experiments which have shown that emotional enhanced memory can be observed even after a short interval. The short-term memory enhancement effect mainly based on the modulation to encode processing ,including increasing attention and fine processing.It had been believed that, the emotion has the priority,and can control attention automaticly,then promote process to emotioal event (bottom-up).But recently, some researchs indicated that the high-level cognition (attention and work memory) may adjust emotion similarly and then modulate process to emotional event (top-down).Therefore, our study is to verify whether different task instructions can affect emotional processing and influence emotional memory through modulating attention and motive . Former study has suggested that different instructions exist different neural mechanism in the emotional expression,but there is no study about whether there exist different neural mechanism in the emotional memory under different instructions. The purpose of this study is to investigate the role of different instructions in emotional processing and memory and its related specific neural mechanism by means of the behavior and fMR study .Materials and Methods 48 healthy adult females, the age scope is 20~25 years old (average age 22.8 years old).These volunteers were divided into stochastically 4 groups according to different instructions and different time.Experimental materials included 288 colored pictures (fear, sad, happy, neutral scene picture,each 72).The experimental task included encoding and retrieving of each kind of scene picture. Time points were divided into two according to encoding and retrieving time interval, which are immediately and 24 hours after.Each time point contains encoding and retrieving task on 4 kinds of scene pictures.The event related design was used in this study and 4 kinds of scene picture had been shown randomly with interval of 6 seconds. All volunteers complete the task under 1.5T GE Signa MRI.The testee was requested to judge emotion intensity or negative /positive for scene picture according to different instructions (encoding stage), then discriminate whether the picture is new or old (retrieving stage)with the aid of the mouse key to express separately.The functional imaging was performed simultaneously. ER-fMRI data and behavior data were analyzed separately with SPM2 and SPSS10.0.Results The emotional picture has a higher hit rate than the neutral picture both in short time-interval (immediately) and long time-interval (24 hours),with great significance(P<0.001), however,this phenomenon only occurred in the long-interva(lP≤0.033) after removing the response bias (d'value). In short-interval, the valence instruction has a higher hit rate of neutral picture than the arousal instruction,with great significanc(eP=0.011), but no difference was found about d'value. In long-interval, arousal instruction has a higher d'value of neutral picture than valence instruction(P=0.034), but no significant difference about the hit rate.In the valence instruction group,the relative specific activative brain areas include left amygdale,right insula, left striatum, cerebellar vermis ,right middle temporal gyrus,bilateral inferior temporal gyrus,medial thalamus,bilateral parietal lobule,bilateral dorsi-lateral prefrontal lobe,right superior frontal gyrus and so on.In the arousal instruction group,the relative specific activative regions, include bilateral cerebellar hemisphere,bilateral fusiform gyrus,right hippocampus,right subiculum hippocampi, bilateral dorsal thalamus,left superior temporal gyrus, left middle temporal gyrus ,bilateral inferior temporal gyrus,left insula, right inferior frontal gyrus, bilateral middle frontal gyrus, bilateral superior frontal gyrus ,callosal gyrus and so on. The long-term memory enhancement effect returns to remarkable correlation with left amygdalae and anterior cingutate under arousal instruction,while it is related to bilateral amygdalae and hippocampus under valence instruction.Conclusions 1.The behavior results indicate that there is no significant difference between arousal and valence instruction in emotional memory ,but there is great difference in non-emotional memory. the arousal instruction effect mainly occurs in long-time stage, and the valence instruction effect mainly occurs in short-time stage. 2.Different task instructions involve in different neural mechanism to modulate emotional processing.The relatively specific brain regions of valence instruction include bilateral dorsolateral prefrontal lobe and left amygdala. The relatively specific brain areas of arousal instruction mainly include bilateral fusiform gyrus and right subiculum hippocampi. 3.The modulation of emotional memory enhancement effect have different mechanism with different instruction. The long-term memory enhancement effect returns to remarkable correlation with left amygdalae and anterior cingutate under arousal instruction,while it is related to bilateral amygdalae and hippocampus under valence instruction.