Whether Are The Memories’ Motivated Forgetting After Sleep Consolidation More Difficult To Occur?-Evidence From Behavior And FMRI

The present study suggested that the motivated forgetting effect is working by the top-down executive control mechanism.And,it is well known sleep can be helpful to humans’ memory consolidation.During sleep,our memories would transfer from the hippocampus to the neocortex.Based on the above two findings,if we want to research the effect of time or circadian rhythm on the motivated forgetting,the sleep is an important factor that not allow to ignore.At the present study,the relationship between sleep and motivated forgetting effect has not yet been determined.If the motivated forgetting effect can also occur in memories after sleep consolidation,we will research the changes in neural mechanisms of this process.Therefore,this research intends to adopt Think/No-Think(TNT)paradigm to study the sleep-related motivated forgetting.The study includes two experiments to research this issue,respectively from the perspective of behavior and brain imaging.This study mainly discusses the influence of circadian rhythm on motivated forgetting,especially sleep.Therefore,the first study aims to explore the relationship between the scores of circadian rhythm questionnaire and the behavior results in TNT paradigm.Then,the second experiment contrast the effect of two kinds of time intervals(nocturnal sleep and daytime awake)for the subsequent motivated forgetting.Combining with previous research,we mainly proposed two assumptions in this study: 1.Sleep is helpful to forgetting.As is known to all,the human’s body function will recovery intensively during the period of sleep.A study has proved that sleep can clean the metabolic wastes and toxins of our brain.Therefore,we assume that sleep can help individuals to recover their executive control ability.Then,in the morning after a whole night sleep they should show the stronger control ability and have advantageous in occurring motivated forgetting successfully.First of all,on the behavior,the success of motivated forgetting may correspond to the separation of sleep and wakefulness group in memory performance,embodied in sleep group,we will observe the motivated forgetting effect significantly,while in awake group,this effect will not occur.Secondly,considering the underlying neural mechanism,the sleep group may take up stronger activation of the dorsolateral prefrontal cortex(dlPFC)and more significantly activated areas than the wake group.2.Sleep is not helpful to forgetting.According to the sleep have more well known effects on memory consolidation,especially the SWS sleep on the declarative memories consolidation,so the memory storage could be better in sleep group.In subsequent motivated forgetting process,the better memory storage means the more memory intrusion,that means the participants need to suffer more interference,so the motivated forgetting effect in sleep group maybe more difficult to happen than the wake group.The above two hypothesis is obtained according to the two different role of sleep in memory associated phenomenon.Both of the two results have rationality to a certain degree,but exist a contradiction objectively.Therefore,the mechanism of motivated forgetting effect after the influence of sleep or wake still don’t know yet,remain to be further inspection in experiments of cognitive neuroscience and psychology.The experiments in this study is designed to solve the puzzle between sleep and memory,mainly to research the influences of sleep on motivated forgetting effect.In the first study,we collected a total of 15 healthy college students’ data.First of all,we asked participants to fill out a questionnaire about circadian rhythm——the morningness-eveningness questionnaire self-assessment(MEQ-SA).And the participants need to complete a whole TNT experiment process.We would calculate the scale scores and the performance of the TNT paradigm.Then,we would analyze the relationship between the scale scores and the results of TNT behavior performance.The second study we used a 2(group: wake,sleep)x3(condition: think,no-think and baseline)two factors mixed design,a total of 40 healthy college students participated in this experiment.The experiment task need to be completed in twice: At the first time,the participants come to the lab,and learn a set of verbal materials(including 64 word-pairs),and training through the "test-feedback" procedure to achieve the recall accuracy of 50% or more,then do the first pretest(pre0).Secondly,we will test the memory performance of all the word pairs again(pretest1,pre1).Then is the core procedure of this experiment——the TNT phase.This phase also divided into two parts,the practice TNT phase and the formal TNT phase.In the practice TNT,we asked participants to acquaint the process by doing the think/no-think operation while we present the reminder with the color rectangle in green/red.Then,we will ask them to fill out a diagnostic questionnaire.The experimenter will check all the items to ensure that the participants understand the experiment task in detail.In formal TNT,the process is corresponding to the practice.And,the participants need concentrate their consciousness on the reminder words framed in different colors and complete three corresponding tasks: when see the cue words framed by red box,they should try their best to stop retrieval of the target items,and keeping this status until next trial begin;when see the cue words in green rectangle,participants are asked to recall the associated target memory;when rectangle’s color is grey,participants don’t need to do any operation,just looking this word passively and keeping their attention the current stimulus on the screen.At the same time,we used fMRI to scan the brain activities during the whole formal TNT process.The behavior results of the first study showed that there is no significant correlation between the circadian rhythm score and motivated forgetting effect.This may be due to the subjects ofsignificant characteristics of circadian rhythm.The behavior results under the TNT paradigm just have a trend of significant motivated forgetting effect.This maybe because of the less amount of behavior experiment subjects.We expected the follow-up researches can draw significant motivated forgetting effect by increasing the amount of participants.The behavior results in the second study showed that: 1.Sleep helps to memory consolidation.Embodied in,on the one hand,after 10 hours interval,the word-pairs recall rate of participants in sleep group is significantly higher than the wake group,directly proved the effect of sleep on memory consolidation.On the other hand,compared the memory performance in pre1 with that in pre0,the recall rate in the wake group is reduced significantly,while the recall rate in the sleep group only changed little.It is suggested that the individuals in wake group have a larger degree of memory loss,indirect evidence the memory consolidation effect of sleep.2.We found the significant motivated forgetting effect only in sleep group,support the first hypothesis——“Sleep is helpful to forgetting”.According to the memory performance of two groups in the final test,we only observed significant motivated forgetting effect in the sleep group;although there are certain trend in the wake group,but did not reach significant level.In addition,according to the analysis of brain imaging data in two groups,we found that the positive activation area is the frontal lobe,and the negative activation areas mainly are the memory related area,include: the parietal lobe,the temporal lobe and hippocampus.There is no significant difference in brain regions of the two groups.Results of the study showed that sleep plays an important role in the executive control mechanism and motivated forgetting.The memories also can be forgotten after the sleep consolidation.Therefore,the mechanism of motivated forgetting can be applied to long-term memory that experienced consolidation of nocturnal sleep.In conclusion,the research results have three important implications: First of all,the motivated forgetting effect can be repeated,and the top-down inhibition control can not only suppress the memories stored in hippocampus,but also can inhibit a more extensive memories storage area or neural circuits.Secondly,memory can benefit from the whole night sleep,and the system consolidation of semantic memories maybe useful over just one night or even more shorter time.Thirdly,sleep is helpful to the occurring of the motivated forgetting effect.The memories experienced sleep consolidation may produce the forgetting in a higher baseline.The effect is stronger than that in wake group,and the requirement of top-down control mechanism is lower.It means a more efficient motivated forgetting.