What does the Human Hippocampus do

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What does the Human Hippocampus do?

• Dharshan Kumaran
• Wellcome Trust Centre for Neuroimaging (UCL)
• Queen Square, London
• \

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• If I was testing your memory...

• Actually not routinely used in clinical
  practice- simplified versionstory recall.

• Patients with hippocampal damage perform find it
  difficult to remember video clips, and similarly
  specific events from their past (e.g.
  conversation with a friend yesterday)

• Remembering video clip is similar to reliving
  personal experiences- episodic memory

• How does Hippocampus support episodic memory (and
  other functions)?

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Whats so special about the hippocampus?
Hippocampus
Retina
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Case H.M

• Severe anterograde amnesia
• Preserved IQ, language, basic perceptual functions

Scoville and Milner, 1957
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Corkin NRN 01

• HM can acquire new information in certain
  settings/tasks

• Consolidation MTL/HC not necessary for remote
  episodic/semantic memory

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Declarative (Textbook) Theory
Larry Squire, UCSD

• HippocampusMTL

• Influential in providing framework for developing
  clinical tests

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MTL Quiz Do you need your MTL to do this task?
Remember bumping into your friend yesterday in
Starbucks
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MTL Quiz Do you need your MTL to do this task?
Imagine you are lying on a beach- dont recall a
specific event from the past, but create
something new
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Empirical Data
YES
Hassabis, Kumaran, Vann, Maguire PNAS 2007
Hassabis, Kumaran, Maguire The Journal of
Neuroscience 2008
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MTL Quiz Do you need your MTL to do this task?
961
623 961
3 sec delay
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MTL Quiz Do you need your MTL to do this task?
3 sec delay
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MTL Quiz Do you need your MTL to do this task?
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Empirical Data
Squire
TASK
YES
YES
Episodic Memory
YES
NO
Imagination
NO
STM- digit
NO
STM- face
YES
NO
YES
Odd-one-out
NO
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Whats Wrong with the Declarative Theory?

• Highly influential e.g. clinical tests
• Evidence that MTL is important for tasks that are
  not declarative
• Implicit memory/ trace conditioning
• Short-term memory
• Perception
• Insufficient level of Explanation

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• Hippocampus as information processing/
  computational device-simulation as goal

• Whats coming in? going out? stored?

• Work back up to episodic memory...

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How can we find out what kind of information the
hippocampus processes?
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Clues from the Anatomy...
Hippocampus
Multimodal, abstract representation (cf V1)
Retina
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• Place cells OKeefe and Dostrovsky 1971. (cf
  V1- orientation tuning)
• Cognitive Map Theory (OKeefe and Nadel, 1978)
• holistic map of spatial environment for spatial
  navigation

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• Place cells OKeefe and Dostrovsky 1971.
• Abstract coding (cf V1- orientation tuning) not
  view sensitive, present in dark.
• Cognitive Map Theory (OKeefe and Nadel, 1978)
• holistic map of spatial environment for spatial
  navigation

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Place cells in the human hippocampus Ekstrom et
al, Nature, 2003
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Morris Water Maze
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London Taxi Drivers
Maguire et al, PNAS 2000
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Hartley et al, Neuron 2003 Maguire et al,
Science 1998
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Space and the Hippocampus

• The hippocampus plays an important role in the
  representation of our spatial environment

Tasks
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Space and the Hippocampus
Tasks
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The Hippocampus represents our spatial environment
But what does this mean?
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Predictions CMT-No RT- Yes
NON-SPATIAL
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Interim Summary

• Declarative Theory- hippocampus/MTL important for
  conscious long-term memory.
• Problems level of explanation/empirical Data
• Hippocampus as information processing device
• Hippocampus and Space
• Hippocampal neurons encode Spatial information
  (place)
• Link to episodic memory
• Space is special
• i.e. Specific role in performing spatial
  computations/spatial processing not
• simply a reflection of associative processing per
  se.

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Temporal Sequence coding

• Reverse Replay of Sequences in the hippocampus

Foster et al, Nature 2006
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Sleep, Dreams, Memory Consolidation....

• Finite storage capacity
• Coordinated replay during SWS between hippocampus
  and cortex makes memories independent of HC
• DreamsReplay?
• Do Amnesics Dream?

Lee and Wilson, Neuron 02
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The Hippocampus and Sequences FMRI
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The Hippocampus and One- Shot Sequence
Storage/Recall FMRI
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Hippocampus Non-Spatial Content

• Role in binding together multiple elements of
  episode into memory trace

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How?
Content
Temporal Sequence

• Recent discovery of MEC Grid cells
• HC integrates parallel streams of spatial and
  non-spatial information CA3
• Spatial/Place representations in HC act as
  scaffold into which other aspects of event
  (sequence, content) are bound- forming episodic
  memory traces

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• Pattern completion

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FORMAL MODEL
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Conclusion

• Problems with Declarative Theory
• Focus on hippocampus as information processing
  device
• Movie clip to illustrate how episodic memory can
  be broken down into different components (place,
  sequence, content) and role of hippocampus in
  each
• Aim is to construct a working computational
  simulation of hippocampus which will generate
  testable predictions
• Ultimate goal is achieve mechanistic
  understanding of why the hippocampus is critical
  to episodic memory...

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Thanks..

• Eleanor Maguire
• Demis Hassabis
• Hugo Spiers
• Benedetto de Martino

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THE END