Neural Mechanisms Of Declarative Memory Reconsolidation

Memory is the process in which the information and experience is acquired,encoded,stored,represented or recalled.It is the fundamental base for other sophisticated cognitive functions,including thought and imagination.The composition,storage and usage of memories are crucial for organisms to adapt to the environment.Memory also plays an important role in the formation of personality and characteristics,as well as in social communication.Generally speaking,memory process is consisted of acquisition(encoding),consolidation,storage,retrieval and reconsolidation.Memory reconsolidation process drew lots of attention in t he memory field in recent years,because of its potential therapeutic implication in some psychological diseases.Previous studies indicate that memory reconsolidation process can be observed in many different memory tasks in various species,although it is not a universal process.However,the mechanisms of declarative memory reconsolidation still remain unclear in human,especially for non-emotional or incentive memory.The current study is trying to investigate the mechanisms underlying non-emotional declarative memory reconsolidation in human,by combining the behavioral and functional MRI studies.The main body of my thesis major contains three parts,introduction,results and discussion.In the Introduction and Review section,the discovery of memory reconsolidation,the similarities and differences between consolidation and reconsolidation were briefly introduced.The detailed discussion on the studies of memory reconsolidation process,especially on the neural mechanisms of reconsolidation was presented.Finally,based on previous studies,the scientific questions and aims,which were investigated in the current study,were raised.The second part contains the experimental designs and results.A new paradigm was designed in the current study,which was called ’face-location associations’ and was applied to four experiments to study the behavioral and neural mechanisms of declarative memory reconsolidation in human.First,we tried to investigate whether reactivate the face-location memory would trigger memory reconsolidation.On day 1,subjects were instructed to remember 30 pairs of face-location.Immediately after retrieval 24 hours later,subjects were asked to memorize anther 30 new sets of face-location.The original memory was tested on day 3.We found that the learning of new sets of face-location immediately after retrieval did not disrupt the reactivated memory.O ne possibility was reactivating the face-location memory did not trigger memory reconsolidation,hence the memory of the old sets of face-location were still intact despite of the new learning.Or reactivating the face-location memory did trigger memory reconsolidation,but learning of the new sets of face-location had no destructive effect on reconsolidation process.To differentiate two possibilities,we applied face-new location as the memory intervention namely same sets of faces were paired with new locations.Other parts remained unchanged.It was found that although memories of both groups decayed,the experimental group showed significant lower accuracy than the control group.This result suggested that the reactivation of the face-location memory indeed triggered memory reconsolidation process,which was disrupted by the new-location-learning.With the purpose to confirm the existe nce of a critical time-window for reconsolidation,we manipulate the duration of the memory retrieval and new-location-learning.Results showed that reconsolidation was significantly disrupted by new-location-learning within 20 minutes after memory reactivation.However,the reconsolidation was not affected when the intervention was administered 30 minutes after memory reactivation.This inferred that there was indeed a critical time-window for reconsolidation,which lasted for about 20 minutes after retrieval.In order to further investigate the neural mechanism of declarative memory reconsolidation,we performed the fMRI studies.Imaging data was collected during the retrieval on both day 2 and day 3 as well as during the initial 20 minutes after retrieval on day 2.Voxel-wised results showed that hippocampus,amygdala and posterior cingulate cortex(precuneus)was activated.Finally,the main findings of this research was concluded and generally discussed.These results provided insights into the mechanisms of declarative memory reconsolidation and suggested that(1)reactivation of declarative memory in human indeed trigger reconsolidation process;(2)declarative memory reconsolidation can be affected by new learning,which should share common components with initial learning;(3)there was indeed a critical time-window of reconsolidation,within which the intervention was able to affect reconsolidation;(4)there might be different mechanisms of disruption of memory reconsolidation;(5)hippocampus,amygdala and posterior cingulate cortex(precuneus)involved in reconsolidation process.Through our study,we hope that we can have some understanding regarding non-emotional declarative memory reconsolidation,and provide theoretical basis for treating some psychological diseases using reconsolidation mechanisms in the future.