心理 101 王雅慧 F OLLOWING THE C ROWD : B RAIN S UBSTRATES OF L ONG -T ERM M EMORY C ONFORMITY

O UTLINE  Introduction  Method  Result  Discussion

I NTRODUCTION  影片

I NTRODUCTION  Our memories are often inaccurate.  Memory conformity : Ubiquitous sources of false recollection are social pressure and interpersonal influence.  Although these social influences on memory have been extensively demonstrated, the underlying neurobiology of this process is unknown.

C ONFORMITY ( 從眾 )  Private Conformity ( 私下從眾 )  an individual’s recollection may genuinely be altered by social influence, resulting in long-lasting, persistent memory errors ( 持久性的記憶錯誤 ).  Public Conformity ( 公開從眾 )  individuals may choose to outwardly comply, providing an account that fits that of others, but inwardly maintain certitude in their own original memory, resulting in transient memory error( 短暫性的記憶錯誤 ).

C ONFORMITY ( 從眾 )  These processes are probably mediated by distinct activation in interconnected brain circuits previously found to be active in mnemonic functions and social cognition (such as the hippocampal complex, amygdala, and frontal regions)

M ETHOD － B EHAVIOR Participant  Thirty right handed subjects (12F,18M) Stimuli  40 minute eyewitness styled documentary Procedure  Encoding phase  Memory Test 1 (day3)  Memory Test 2 ： Manipulation phase (day7)  Memory Test 3 (day14)

M ETHOD － B EHAVIOR Procedure  Encoding phase  viewed an eyewitness-style documentary movie on a large screen in groups of five.  Memory Test 1 (day3)  a memory test:400 questions, two-forced choice  rated how confidence they were after memory test.  assess the participants’ baseline accuracy and confidence.

M ETHOD － B EHAVIOR Procedure  Memory Test 2 ： Manipulation phase (day7)  performed a memory test while in an fMRI scanner  The questions were identical to those in Test 1.  Before answering the question, participants were presented with answers they were led to believe were given by their four fellow co-observers co-observer’s photo and answer

M ETHOD － B EHAVIOR Procedure  Memory Test 2 ： Manipulation phase (day7) (cont.) Three Conditions  Manipulation the answers provided by the four co-observes were all false.(80 questions)  No- Manipulation the letter X was presented instead of the co- observers’ answers (25 questions).  Credibility to prevent the answers from fabricating because of suspicion.

M ETHOD － B EHAVIOR Procedure  Memory Test 3 (day14)  were informed that the answers given by the co- observers during the previous fMRI session were in fact determined randomly.  after informing, the participants were then requested to complete the memory test in scanner again.

R ESULT -B EHAVIOR  Behavioral data revealed that manipulation induced memory errors.  Participants conformed to the majority opinion.  Not due to forgetting. Lower error rate in no-manipulation conditions.

R ESULT -B EHAVIOR  Social influence was removed (test 3)  participants maintained erroneous answers in 40.8% of the previously conformed trials (persistent errors).  participants reverted to their original correct answer in 59.2 % of the previously conformed trials (transient errors)

R ESULT -B EHAVIOR  Confidence ratings  No difference either before or after the manipulation stage.(persistent and transient errors)  During the manipulation stage, confidence ratings in transient errors were significantly lower than in persistent errors.

R ESULT  Regions of interest (ROIs)  A-priori anatomical ROIs Memory encoding and maintenance bilateral anterior hippocampus bilateral posterior hippocampus bilateral parahippocampal gyrus social-emotional processing bilateral amygdala

R ESULT  The BOLD (Blood Oxygenation Level Dependent) signal : persistent errors ＞ transient errors or nonconformity (In all regions except for the left posterior hippocampus)  No significant difference was found between transient error and nonconformity trials BOLD

R ESULT  Whole-brain exploratory analysis  persistent errors ＞ transient errors greater activity in four regions, all in medial temporal lobe.  left amygdala  right hippocampus  right parahippocampal gyrus (PHG)  a region bordering the left PHG and occipital cortex  transient errors ＞ persistent errors  enhanced activation was in the bilateral dorsal anterior cingulate cortex

R ESULT  Amygdala  plays a key role in social and emotional processing and modulates memory related hippocampal activity.  rich anatomical connections with the hippocampal complex and with neocortical areas.  A striking activation was found in the left amygdala.  Heightened activation in the amygdala was not due to heightened emotional arousal, seemed specific to socially induced memory change.

R ESULT  Psychophysiological interaction(PPI) A method for finding out whether the correlation in activity between two distant brain areas is different in different psychological contexts.  This analysis showed heightened functional connectivity between the left amygdala and bilateral anterior hippocampus (ROIs), during trials that subsequently resulted in persistent memory errors as opposed to transient errors and nonconformity.

R ESULT -B RAIN IMAGE  Information was presented(manipulation relative to no-manipulation conditions)  Frontal regions ： bilateral inferior frontal gyrus,dorsal ACC, dorsal medial pre-frontal cortex 。  occipital cortex  Further analysis of brain activity in these regions suggests that they are involved in non-mnemonic processes, such as conflict monitoring in the face of competing memories.

R ESULT  Were our findings driven merely by the presentation of additional information regardless of social context?  Control Study : Non-social  information → four different computer algorithms.  Behavior (Conformity): Social manipulation ＞ non-social ＞ no-manipulation  Brain image : Bilateral amygdala: greater activation in the social manipulation, but not in the nonsocial manipulation. →enhanced activity in these regions is related specifically to socially induced persistent memory errors.

R ESULT  Brain image(cont.) : Right anterior, posterior hippocampus, left PHG: No difference in any manipulation type. →long lasting memory errors irrespective of the medium by which information was conveyed. left amygdala, bilateral anterior hippocampus : a significant interaction. → a pattern specific to the social manipulation  Heightened amygdala activation and enhanced connectivity with the hippocampus are specific to socially induced memory changes.  Hippocampal complex activation differentiates between persistent and transient errors regardless of the source of influence.

D ISSCUSSON -1  Results indicate that memory is highly susceptible to alteration due to social influence, creating both transient and persistent errors.  A mechanism by which social influence produces long- lasting alterations in memory.  The critical role of the amygdala in mediating this influence.

D ISSCUSSON -2  Heightened activation in the hippocampal complex was seen when false information induced a long- lasting change in the participants’ memories regardless of social context.  The hippocampal complex activation may represent a process of reconsolidation or encoding of new stable representations

D ISSCUSSON -3  Enhanced activation in the bilateral amygdala and heightened functional connectivity with the anterior hippocampus.  signature of long term memory change induced by the social environment.  mediation of amygdala  neurobiological evidence for memory conformity.