Transcript schacter-banbury-2009

Episodic Simulation of Future Events
and the Medial Temporal Lobe
Daniel L. Schacter
Harvard University
Banbury Center, April 13, 2009
Amnesic Patient KC: No Past, No Future
Tulving, Canadian Psychology (1985)
Commonalities between Past and Future Events
* 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)
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 the
Past, Imagining the Future, & Related Forms of Mental Simulation
Schacter, Addis, & Buckner, Nature Reviews Neuroscience (2007)
Constructive Episodic Simulation Hypothesis
(Schacter & Addis, 2007, Nature; Phil.Trans. Royal Society B)
– 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.
Past & Future: A Neuroimaging Approach
•
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 and Future: Common Neural Substrates?
CONSTRUCTION
CUE
0
2
ELABORATION
RT
RATINGS
20
• 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
35 time
•3 scales,
shown
consecutively
each for 5 s
Detail
12345
FUTURE event
PAST event
Last 5-20 yrs
CAR
OR
Next year
DRESS
task
time-period
Emotion
cue
12345
Perspective
field/observer
Past and Future: Control Tasks
CONSTRUCTION
CUE
0
2
ELABORATION
RT
RATINGS
20
• 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
35 time
•3 scales,
shown
consecutively
each for 5 s
Detail
12345
WORDS-sentence
2 related words
CABLE
OBJECTS- triangle
OR
bigger / smaller
LEAF
task
items to generate
cue
Relatedness
12345
Difficulty
easy / difficult
Past and Future Events: Common Neural Substrates?
CUE
CONSTRUCTION
ELABORATION
OVERLAP:
FUSIFORM & R. MIDDLE OCCIPITAL
Cue processing / object recognition
past events
future events
L. HIPPOCAMPUS
Initial retrieval
control tasks
Construction: Neural differentiation
CUE
CONSTRUCTION
ELABORATION
future > past
R. HIPPOCAMPUS
R. FRONTAL POLE (BA 10)
Novelty encoding?
Recombining details
to form specific
episodes ?
past events
future events
Novelty / Recombining details
control tasks
Past and Future Events: Common Neural Substrates?
CUE
CONSTRUCTION
ELABORATION
L. FRONTAL POLE
OVERLAP:
L. HIPPOCAMPUS
Self referential processing
L. TEMPORAL POLE
Conceptual details
past events
Reintegrate/recombine
event details
MEDIAL PARIETAL / PARAHIPPOCAMPUS
Imagery / context
future events
control tasks
Past and Future Detail
Background
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 Detail
Method
CONSTRUCTION
CUE
0
2
RATE DETAIL
ELABORATION
RT
20
25
time
RECALL PAST
Last 5-20 yrs
CAR
IMAGINE FUTURE
Next year
RATE DETAIL
12345
RATE DETAIL
12345
DRESS
– Past & future detail did not differ on average
– Parametric modulation: what regions vary with amount of detail?
Past and Future Detail
Addis and Schacter (2008, Hippocampus)
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)
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 or
associated with more general imagination/simulation?
According to constructive episodic simulation hypothesis,
critical process of recombining event details should occur
regardless of whether individuals imagine an event as occurring
in 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 that
subjects simply remember entire events and recast them
in 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 required
to recombine elements of different episodes?
fMRI Paradigm: Experimental Recombination of Details
IMAGINE PAST
MEMORY POOL
IMAGINE FUTURE
Imagine PAST event:
Fall outside library
PERSON: Katie
LOCATION: Widener
OBJECT: Hat
Imagine FUTURE event:
Mom: Graduation Day
Filipes: Meeting Cathy
Gown: Graduation Day
RECALL TASK
Graduation Day
PERSON: Mom
LOCATION: Harvard Yard
OBJECT: Gown
RECALL memories:
Cathy: Meeting Cathy
Widener: Fall outside library
Hat: Fall outside library
Meeting Cathy
PERSON: Cathy
LOCATION: Filipes
OBJECT: Fajita
Katie: Fall outside library
Harvard Yard: Graduation Day
Fajita: Meeting Cathy
CONTROL TASK
CREATE SENTENCE
Start with smallest:
Cat: Include cat in sentence
Bulb: Include bulb in sentence
Tree: Include tree in sentence
fMRI Paradigm:
CONSTRUCTION
CUE
0
2
RATE DETAIL
ELABORATION
RT
24
25
Imagine PAST event :
Mom: Graduation Day
Filipes: Meeting Cathy
Gown: Graduation Day
RATE DETAIL
Button press when
event is in mind
12345
Imagine FUTURE event :
Katie: Fall outside library
RATE DETAIL
Harvard Yard: Graduation
12345
Fajita: Meeting Cathy
Recall MEMORIES:
Cathy: Meeting Cathy
RATE DETAIL
Widener: Fall outside library
12345
Hat: Fall outside library
time
Experimental Recombination Task
Common Core Network
Future-Imagine, Past-Imagine & Past-Recall > Control Task
Lateral temporal lobe
Bilateral hippocampus
Cuneus
Retrosplenial / precuneus
Medial prefrontal / frontal
poles
Lateral parietal lobe
Retrosplenial / precuneus
Addis, Pan, Vu, Laiser, & Schacter (in press, Neuropsychologia)
Experimental Recombination Task
Imagining Subsystem?
Future-Imagine and Past-Imagine > Control Task
Lateral temporal lobe
Bilateral hippocampus
Retrosplenial / precuneus
Medial prefrontal / frontal
poles
Lateral parietal lobe
Retrosplenial / precuneus
Experimental Recombination Task
Remembering Subsystem?
Past-Recall > Past-Imagine, Future-Imagine & Control Task
Cuneus
Middle/inferior occipital gyrus
Conclusions
(see Schacter & Addis, 2009, Phil. Trans. Roy. Soc.)
• 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.
Acknowledgements
Memory Lab, Harvard
Brendan Gaesser
Kathy Gerlach
Adrian Gilmore
Yoko Okado
Ling Pan
Jessica Payne
Nathan Spreng
Dale Stevens
Gagan Wig
Collaborators
Donna Addis
Randy Buckner
Theresa Cheng
Elizabeth Chua
Noa Laiser
Ling Pan
Alana Wong
Supported by NIMH & NIA