Daniel L. Schacter

1
Episodic Simulation of Future Events
and the Medial Temporal Lobe

• Daniel L. Schacter
• Harvard University

Banbury Center, April 13, 2009
2
Amnesic Patient KC No Past, No Future
Tulving, Canadian Psychology (1985)
3
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
• (DArgembeau 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)
4

• Core Network of Regions Involved in
  Remembering the
• Past, Imagining the Future, Related Forms of
  Mental Simulation

Schacter, Addis, Buckner, Nature Reviews
Neuroscience (2007)
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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.

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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)

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Past and Future Common Neural Substrates?
RATINGS
CONSTRUCTION
ELABORATION
CUE
0
20
2
RT
35
time

• 3 scales, shown consecutively each for 5 s

• 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

Detail 1 2 3 4 5
PAST event Last 5-20 yrs CAR
FUTURE event Next year DRESS
task
Emotion 1 2 3 4 5
OR
time-period
cue
Perspective field/observer
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Past and Future Control Tasks
RATINGS
CONSTRUCTION
ELABORATION
CUE
0
20
2
RT
35
time

• 3 scales, shown consecutively each for 5 s

• 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

Detail 1 2 3 4 5
task
WORDS-sentence 2 related words CABLE
OBJECTS- triangle bigger / smaller LEAF
Relatedness 1 2 3 4 5
OR
items to generate
cue
Difficulty easy / difficult
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Past and Future Events Common Neural Substrates?
CUE
CONSTRUCTION
ELABORATION
OVERLAP
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Construction Neural differentiation
CUE
CONSTRUCTION
ELABORATION
future past

• R. HIPPOCAMPUS

• R. FRONTAL POLE (BA 10)

• Novelty encoding?
• Recombining details
• to form specific episodes ?

Novelty / Recombining details
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Past and Future Events Common Neural Substrates?
CUE
CONSTRUCTION
ELABORATION
OVERLAP
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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

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Past and Future Detail Method
CONSTRUCTION
ELABORATION
RATE DETAIL
CUE
0
2
20
25
RT
time
RATE DETAIL 1 2 3 4 5
RECALL PAST Last 5-20 yrs CAR
RATE DETAIL 1 2 3 4 5
IMAGINE FUTURE Next year DRESS

• Past future detail did not differ on average
• Parametric modulation what regions vary with
  amount of detail?

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Past and Future Detail Addis and Schacter (2008,
Hippocampus)

• Posterior HC activity correlates
• with past AND future detail
• Retrieval of details from
• past events?

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Hippocampal Response to Recombined Details
Preston et al. (2004) Recombined details engage
anterior hippocampus
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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.
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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?
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fMRI Paradigm Experimental Recombination of
Details
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fMRI Paradigm
CONSTRUCTION
ELABORATION
RATE DETAIL
CUE
0
2
24
25
RT
time
Imagine PAST event Mom Graduation Day Filipes
Meeting Cathy Gown Graduation Day
RATE DETAIL 1 2 3 4 5
Button press when event is in mind
Imagine FUTURE event Katie Fall outside
library Harvard Yard Graduation Fajita Meeting
Cathy
RATE DETAIL 1 2 3 4 5
Recall MEMORIES Cathy Meeting Cathy Widener
Fall outside library Hat Fall outside library
RATE DETAIL 1 2 3 4 5
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Experimental Recombination Task
Common Core Network
Future-Imagine, Past-Imagine Past-Recall
Control Task
Lateral temporal lobe Bilateral hippocampus
Lateral parietal lobe Retrosplenial / precuneus
Cuneus Retrosplenial / precuneus Medial
prefrontal / frontal poles
Addis, Pan, Vu, Laiser, Schacter (in press,
Neuropsychologia)
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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
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Experimental Recombination Task
Remembering Subsystem?
Past-Recall Past-Imagine, Future-Imagine
Control Task
Cuneus Middle/inferior occipital gyrus
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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.

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Acknowledgements
Memory Lab, Harvard Collaborators Brendan
Gaesser Donna Addis Kathy Gerlach Randy
Buckner Adrian Gilmore Theresa Cheng Yoko
Okado Elizabeth Chua Ling Pan Noa
Laiser Jessica Payne Ling Pan Nathan
Spreng Alana Wong Dale Stevens Gagan
Wig Supported by NIMH NIA