Founctional MRI Of Sustained And Transient Effects On Emotional Memory: A Comparative Study Between The Young Adults And The Old

Background and Objective Emotional memory is also called emotion arousal episodic memory.Emotional event is more easily remembered than non-emotional event,which is so-called emotion enhancement effect.The reason for emotion enhancenment effect is that emotion can modulate each stage of memory process including encode,consolidation and retrieval.It manily modulated perception,attention and fine process in encoding stage.The related studies usualy used event-related or block disgen.The former mainly reflects transient effect of perception but can't reflect sustained effect of emotion and cognitive,while the latter could reflect the sustained attention and arousal state but it is aslo affected by transient effect.Therefore,it is difficut to completly reflect the specific emotion effect on memory with the above two designs.Recent study with fMRI indicated that mixed trial design of event-related with blocked design could investigate the sustained and transient effect in the encoding process for memory simultaneously.By now,there have no report about the study on emotion memory by means of this design.Moreover,former studies usally give foucs on young adult.Generaly speaking,the congnition function including attention retain and memory declined in older than that in young adults,that is so-called age effect.However, rencent study found that there in no age effect on emotion process and there is positive emotion bias in the old.The mechanism about emotion bias is still unclear.It is necessary to have further study about whether there is relation between emotion sustained and transient effect on emotion bias.The purpose of this study is to investigate the difference of the sustained and transient effect in emotion memory between the young and old,and the specific mechanism about emotional memory of the old.Materials and Methods Twelve healthy old(6 males) and 25 young(12males) were invovled in this study.The old participants aged from 62 to 74 years old(average age 68). The younger participants aged from 20 to 24 years old(average age 21.7).Two hundred and forty pictures were used for this experiment,which included 4 kinds of pictures with fear,happy,sad,and neutral scene,60 pictures for each.Both encoding and retrieving period were invovled in the experimental process.The mixed design of event-related and block was used in encoding task.MRI scaning and the data acqusition were performed when the testee are carrying on the encoding task.In the retrieval stage,the testee were requested to discriminate wether the picture is new or old and the behavioral results were recorded,fMRI and behavioral data were analyzed with SPM99/SPM2 and SPSS10.0 software.Results The behavioral results indicated that there were significant differences in memory performance of all scene pictures between the young and the old(P＜0.01).The performance of fear is the best and performance of sad is the worst in the young.There is significan difference between the fear/sad and others(P＜0.05).The performance of fear is best in the old.There is significan difference between fear and sad,neutral picture.There is also significant difference between happy and sad picture(P＜0.05).fMRI results suggested that it is mainly related to sustained effect for emotion enhancement in the young.The brain region related to fear included bilateral amygdala,left hippocampus,and right prefrontal cortex.The brain region related to happiness included left hippocampus,left amygdala,and left prefrontal cortex.It is mainly related to transient effect for emotion enhancement in the old.The brain region related to fear included left amygdala,right hippocampus,bilateral prefrontal cortex and the brain region related to happiness included left amygdala,bilateral hippocampus,and bilateral prefrontal cortex. Conclusions The immediate memory declined in the old,but there still exists emotional enhancement effect and relative positive bias.Sustained and transient effect play different role in the emotional memory of the young and old.The emotional enhancement effect mainly depends on sustained effect in the young,while the emotional enhancement effect mainly depends on transient effect in the old,which are related to medial temporal lobe and prefrontal lobe.Function of medial temporal lobe reduces in the old,while prefrontal cortex compensates.