Daniel L. Schacter Harvard University
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Transcript of Daniel L. Schacter Harvard University
Daniel L. Schacter Harvard University
Episodic Simulation of Future Events and the Medial Temporal Lobe
Banbury Center, April 13, 2009
Amnesic Patient KC: No Past, No Future
Tulving, Canadian Psychology (1985)
* Amnesic patients: Difficulties imagining personal futures/novel scenes(Tulving, 1985; Klein, Loftus, & Kihlstrom, 2002; Hassabis et al., 2007)
* Depressed patients/older adlts: Reduction in episodic specificity of past events and future events significantly correlated (Williams et al., 1996; Addis, Wong, & Schacter, 2008)
* Cognitive studies: Manipulations/individual differences similarly influence past and future events (D’Argembeau & van der Linden, 2004; 2006; Spreng & Levine, 2006)
• Neuroimaging: Similar areas active when remembering past and imagining future (Addis, Wong, & Schacter, 2007; Hassabis et al., 2007; Okuda et al.,
2003; Szpunar, Watson, & McDermott, 2007)
Commonalities between Past and Future Events
Reviewed by Schacter, Addis, & Buckner, Nature Reviews Neuroscience (2007);Year in Cognitive Neuroscience, Annals of the NY Academy of Sciences (2008)
Core Network of Regions Involved in Remembering thePast, Imagining the Future, & Related Forms of Mental Simulation
Schacter, Addis, & Buckner, Nature Reviews Neuroscience (2007)
– Episodic memory involves constructive processes: *Details are stored as fragments in cortical regions; during retrieval they
are reactivated by these cortices and reintegrated by hippocampus into a coherent event.
– The constructive nature of episodic memory makes it well-suited to building simulations of possible future events: *Enables one to extract details from past events
*Enables the flexible recombination of details from past events into coherent future scenarios – which likely relies heavily on relational processing capacities supported by the hippocampal region.
– Though well-suited to simulating future events, constructive nature of episodic memory has a cost:
*Miscombination of details can result in memory errors such as false recognition.
Constructive Episodic Simulation Hypothesis (Schacter & Addis, 2007, Nature; Phil.Trans. Royal Society B)
• We used event-related fMRI to examine the neural substrates of past and future event construction and elaboration; focus on everyday autobiographical events
• Instructions (14 young adult participants):–Cued to recall past event or imagine future event–Future events should be novel and plausible–Three time periods for both past and future:last/next week, last/next year, last/next 5-20 yrs.
Subjects describe events in post-scan interview
Addis, Wong, & Schacter (Neuropsychologia, 2007)
Past & Future: A Neuroimaging Approach
Past and Future: Common Neural Substrates?
CUECUE CONSTRUCTIONCONSTRUCTION ELABORATIONELABORATION
PAST event
Last 5-20 yrs
CAR
FUTURE event
Next year
DRESS
time-periodtask
cue
0
• Event cue screen presented for 20 s
• Button press made when event in mind – signifies end of construction & beginning of elaboration
•24 past and 24 future event task trials
20 time
OR
2 RT
RATINGSRATINGS
•3 scales, shown consecutively each for 5 s
35
Detail
1 2 3 4 5
Emotion
1 2 3 4 5
Perspective
field/observer
CUECUE CONSTRUCTIONCONSTRUCTION ELABORATIONELABORATION
items to generate
task
cue
0
• Event cue screen presented for 20 s
• Button press made when event in mind – signifies end of construction & beginning of elaboration
•24 semantic and 24 visuospatial task trials
20 time
OR
2 RT
RATINGSRATINGS
•3 scales, shown consecutively each for 5 s
35
Detail
1 2 3 4 5
Relatedness
1 2 3 4 5
Difficulty
easy / difficult
WORDS-sentence
2 related words
CABLE
OBJECTS- triangle
bigger / smaller
LEAF
Past and Future: Control Tasks
CUE CONSTRUCTIONCONSTRUCTION ELABORATION
FUSIFORM & R. MIDDLE OCCIPITAL L. HIPPOCAMPUS
Cue processing / object recognition Initial retrieval
past events future events control tasks
OVERLAP:
Past and Future Events: Common Neural Substrates?
Construction: Neural differentiation
CUE CONSTRUCTIONCONSTRUCTION ELABORATION
future > past
R. FRONTAL POLE (BA 10)
Novelty / Recombining details
R. HIPPOCAMPUS
Novelty encoding? Recombining details
to form specific episodes ?
past events future events control tasks
CUE CONSTRUCTION ELABORATIONELABORATION
L. FRONTAL POLE L. HIPPOCAMPUS
Self referential processing Reintegrate/recombine event details
L. TEMPORAL POLE MEDIAL PARIETAL / PARAHIPPOCAMPUS
Conceptual details Imagery / context
past events future events control tasks
OVERLAP:
Past and Future Events: Common Neural Substrates?
Are hippocampal responses to detail similar for past and future events?
Constructive Episodic Simulation Hypothesis:– Past events: reintegration of relevant event details– Future events: recombination of various details into novel event
Past and Future DetailBackground
RECALL PAST
Last 5-20 yrs
CAR
IMAGINE FUTURE
Next year
DRESS
0 2 20 timeRT 25
RATE DETAIL
1 2 3 4 5
RATE DETAIL
1 2 3 4 5
– Past & future detail did not differ on average
– Parametric modulation: what regions vary with amount of detail?
Past and Future DetailMethod
CUE CONSTRUCTION ELABORATIONELABORATION RATE DETAIL
Posterior HC activity correlates with past AND future detail:
- Retrieval of details from past events?
More anterior HC activity correlates with future detail
- Flexible recombination of details from past events? Cf. Preston et al. (2004)
Past and Future DetailAddis and Schacter (2008, Hippocampus)
Hippocampal Response to Recombined Details
Preston et al. (2004): Recombined details engage anterior hippocampus
Constructive Episodic Simulation: Two Conceptual Issues
1. Comparison has focused on remembering the past vs. imagining the future, but past/future confounded with remembering/imagining:
Are observed patterns specific to imagining future events orassociated with more general imagination/simulation?
According to constructive episodic simulation hypothesis,critical process of recombining event details should occurregardless of whether individuals imagine an event as occurringin the future, present, or past.
Constructive Episodic Simulation: Two Conceptual Issues
2. Constructive episodic simulation hypothesis emphasizes recombining of details across events, but it is possible thatsubjects simply remember entire events and recast themin the future.
In previous studies, future simulations could be based on recasting, recombining, or some combination of the two.
Are main effects still observed when individuals are requiredto recombine elements of different episodes?
fMRI Paradigm: Experimental Recombination of Details
Fall outside libraryPERSON: Katie
LOCATION: WidenerOBJECT: Hat
Graduation DayPERSON: Mom
LOCATION: Harvard YardOBJECT: Gown
Meeting CathyPERSON: Cathy
LOCATION: FilipesOBJECT: Fajita
MEMORY POOLImagine PAST event:
Mom: Graduation DayFilipes: Meeting CathyGown: Graduation Day
IMAGINE PAST
RECALL TASKRECALL memories:
Cathy: Meeting CathyWidener: Fall outside library
Hat: Fall outside library
Imagine FUTURE event:
Katie: Fall outside libraryHarvard Yard: Graduation Day
Fajita: Meeting Cathy
IMAGINE FUTURE
CONTROL TASKCREATE SENTENCEStart with smallest:
Cat: Include cat in sentenceBulb: Include bulb in sentenceTree: Include tree in sentence
fMRI Paradigm:
CUE CONSTRUCTION ELABORATION
Imagine FUTURE event :Katie: Fall outside library
Harvard Yard: Graduation
Fajita: Meeting Cathy
Button press when event is in mind
0 2 24 timeRT 25
RATE DETAIL
RATE DETAIL
1 2 3 4 5
RATE DETAIL
1 2 3 4 5
Imagine PAST event :Mom: Graduation Day
Filipes: Meeting Cathy
Gown: Graduation Day
Recall MEMORIES:Cathy: Meeting Cathy
Widener: Fall outside library
Hat: Fall outside library
RATE DETAIL
1 2 3 4 5
Experimental Recombination Task Common Core Network
Addis, Pan, Vu, Laiser, & Schacter (in press, Neuropsychologia)
Future-Imagine, Past-Imagine & Past-Recall > Control Task
Lateral temporal lobeBilateral hippocampus
CuneusRetrosplenial / precuneusMedial prefrontal / frontal poles
Lateral parietal lobeRetrosplenial / precuneus
Experimental Recombination TaskImagining Subsystem?
Future-Imagine and Past-Imagine > Control Task
Lateral temporal lobeBilateral hippocampus
Retrosplenial / precuneusMedial prefrontal / frontal poles
Lateral parietal lobeRetrosplenial / precuneus
Experimental Recombination Task
Remembering Subsystem?
Past-Recall > Past-Imagine, Future-Imagine & Control Task
CuneusMiddle/inferior occipital gyrus
• Constructive nature of the episodic memory system: during retrieval, various elements of past experiences are reintegrated and recombined, allowing us to draw on the past to imagine the future.
• Imaging data support the constructive episodic simulation hypothesis - and the possibility that simulation of future events is a primary function of a constructive episodic memory.
• The hippocampus plays an important role in recombining and encoding details from past episodes into
simulations of the future. Converging evidence from work on prospective coding/preplay of event sequences.
Conclusions(see Schacter & Addis, 2009, Phil. Trans. Roy. Soc.)
Acknowledgements
Memory Lab, Harvard CollaboratorsBrendan Gaesser Donna AddisKathy Gerlach Randy BucknerAdrian Gilmore Theresa Cheng Yoko Okado Elizabeth Chua Ling Pan Noa LaiserJessica Payne Ling PanNathan Spreng Alana Wong Dale StevensGagan Wig
Supported by NIMH & NIA