心理 101 王雅慧

FOLLOWING THE CROWD:BRAIN SUBSTRATES OF LONG-TERM MEMORY CONFORMITY

OUTLINE

Introduction

Method

Result

Discussion

INTRODUCTION

影片

http://www.youtube.com/watch?v=bDu-2UosnEQ&hd=1

INTRODUCTION

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.

CONFORMITY( 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 ).

CONFORMITY( 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)

METHOD － BEHAVIOR

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)

METHOD － BEHAVIOR

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.

METHOD － BEHAVIOR

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

METHOD － BEHAVIOR

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.

METHOD － BEHAVIOR

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.

RESULT-BEHAVIOR

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.

RESULT-BEHAVIOR

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)

RESULT-BEHAVIOR

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 .

RESULT

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

RESULT

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

RESULT

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

RESULT

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.

RESULT

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.

RESULT-BRAIN 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 .

RESULT

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.

RESULT

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.

DISSCUSSON-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.

DISSCUSSON-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

DISSCUSSON-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.