Kumaran_talk by niusheng11

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									What does the Human
Hippocampus do?


Dharshan Kumaran
Wellcome Trust Centre for
Neuroimaging (UCL)
Queen Square, London
    If I was testing your memory...

   Actually not routinely used in clinical practice-
simplified version=story 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)?
What‟s so special about the hippocampus?



 Hippocampus




   Retina
Case H.M




              Severe       anterograde
           amnesia
             Preserved IQ, language,
           basic perceptual functions




             Scoville and Milner,
             1957
                             Hippocampus

             Dentate Gyrus




              Subiculum

              Perirhinal Cortex
Entorhinal
Cortex
                                   Corkin NRN 01



                                     HM can acquire new
                                 information in certain
                                 settings/tasks
                                     Consolidation:
                                 MTL/HC not necessary
                                 for                remote
                                 episodic/semantic
                                 memory




Cohen and Squire, Science 1980
Declarative (“Textbook”)
Theory
                                                                                     Larry Squire, UCSD
    MTL-Independent                                           MTL-Dependent

                        STM
                                                                     Episodic
              e.g. memory over seconds
                                                           e.g. What did I do yesterday?

 Procedural                    Perception
                                                                                  Semantic
                              i.e. “seeing”
e.g. riding a bicycle                                             e.g. What is the capital of France?


                                                               Recognition Memory
          Conditioning
                                                         e.g. Have I seen this person before?
       e.g. Pavlovian conditioning




                        Hippocampus==MTL
                        Influential in providing framework for developing clinical tests
 “MTL Quiz: Do you need your MTL to do this
                  task?”

“Remember bumping into your friend yesterday
             in Starbucks”



                          Squire          YES



                          Empirical Data YES
 “MTL Quiz: Do you need your MTL to do this
                  task?”


“Imagine you are lying on a beach- don‟t recall a specific
          event from the past, but create something new”




                                   Squire              NO
         Empirical Data YES
      Hassabis, Kumaran, Vann, Maguire PNAS 2007;
Hassabis, Kumaran, Maguire The Journal of Neuroscience 2008
“MTL Quiz: Do you need your MTL to do this
                 task?”



  961                     623 961

            3 sec delay
                          Squire           NO



                          Empirical Data     NO
“MTL Quiz: Do you need your MTL to do this
                 task?”




            3 sec delay
                                   Squire                               NO



                                   Empirical Data YES
                 Ranganath et al, Neuron 2002; Nichols et al, Hippocampus 2006
“MTL Quiz: Do
you need your
MTL to do this
                 Squire                         NO
    task?”


                 Empirical Data                 YES
                  Lee et al, Hippocampus 05
                  (but see Shrager et al, 06)
                  Squire Empirical Data

   TASK


Episodic Memory    YES       YES

Imagination         NO       YES

 STM- digit         NO        NO

 STM- face          NO       YES

Odd-one-out         NO       YES
What‟s 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
DECLARATIVE                        Tasks           Episodic Memory
  THEORY                                            X motor memory
                                                       X STM




  INPUTS                                                       OUTPUTS




    Hippocampus      as  information          What‟s coming in? going out?
  processing/ computational device-        stored?
  simulation as goal
                                            Work back     up   to    episodic
                                           memory...
How can we find out what
  kind of information the
hippocampus processes?
Clues from the Anatomy...


  Hippocampus

                                Firing rate




                                       Orientation coding in V1
                                      (Hubel and Wiesel 1968)



                            Multimodal, abstract representation (cf
                            V1)

    Retina
•Place cells: O‟Keefe and Dostrovsky 1971. (cf V1- orientation tuning)

•Cognitive Map Theory (O‟Keefe and Nadel, 1978)

       • holistic map of spatial environment for spatial navigation
•Place cells: O‟Keefe and Dostrovsky 1971.

•Abstract coding (cf V1- orientation tuning): not view sensitive, present in dark.

•Cognitive Map Theory (O‟Keefe and Nadel, 1978)

       • holistic map of spatial environment for spatial navigation
Place cells in
 the human
hippocampus
Ekstrom et al,
Nature, 2003
Morris Water Maze
London Taxi Drivers




                      Maguire et al, PNAS 2000
        FMRI

 *fMRI allows neural activity in a
given brain region to be inferred
  from measured T2* parameter
which is influenced by changes in
             blood flow

 *High Resolution fMRI: identify
     separate subregions of
         hippocampus




      Hartley et al, Neuron 2003
      Maguire et al, Science 1998
Space and the                         The     hippocampus      plays   an
Hippocampus                        important role in the representation of
                                   our spatial environment


         Tasks

    Spatial Navigation (e.g. AD)




   Object Positions




                                                                             Place

   Link to Episodic Memory
Space and the
Hippocampus
       Tasks
 Imagination




Scene Perception
                 The Hippocampus
               represents our spatial              Baker St
                                                              Kings cross

                   environment
             But what does this mean?


Spatial computations           Proficient Linker/Associator

Cognitive Map Theory                Relational Theory
                                    (Cohen and Eichenbaum 1993)
   (O‟Keefe and Nadel, 1978)
Cognitive map                                      Relational Theory
 SPATIAL                                           DOMAIN-GENERAL

Baker St
           Kings cross            Jon
                                            Ruth




                                                                       Parameter       Soc   Spa
                                                                                       R     R
                                                                       Performance     74    80
                                                                       Difficulty      6.0   6.3
                         Alan
                                                                       Time on task    1.6   1.4
Places in London                                    Predictions
                                Social Network                         „Knowing‟       5     1.6
                                                    CMT-No
    SPATIAL                     NON-SPATIAL         RT- Yes            „Location‟      1.3   5
                                                                       Episodic        3.0   2.3
                                                                       Memory
                                                                        Emotional      1.3   0.9
                                                                        Self-related   2.5   2.3
                                                                        Imagery        2.5   3


                                                                  Kumaran and Maguire,
                                                                  Journal of Neuroscience
                                                                  2005
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.
Place
        Temporal Sequence


                            Content
Temporal Sequence coding




                            Reverse Replay of
                         Sequences in the
                         hippocampus




                      Foster et al, Nature 2006
 Sleep, Dreams, Memory                       Run Trial

     Consolidation....




  Finite storage capacity
  Coordinated replay during SWS
between hippocampus and cortex
                                         Lee and Wilson, Neuron 02
makes memories independent of HC
  Dreams=Replay?                   Sleep (SWS)
  Do Amnesics Dream?
The Hippocampus and
  Sequences: FMRI



Face Sequence     A       B       C       D       E       F    G   H     I   J    K    L
                                                          e.g. Kumaran and Maguire, Neuron
                                                                        2006




 Motor Sequence       1       3       4       1       2     4     2     3       1   4   1        3



                                                          e.g. Fletcher et al, Cerebral Cortex
                                                            04, Schendan et al, Neuron 03


                                                          Implicit/Explicit
                                                          Multitrial learning
The Hippocampus and
 One- Shot Sequence
Storage/Recall: FMRI




          Kumaran and Maguire, PLoS Biology 2006
Place
        Temporal Sequence


                            Content
Hippocampus: Non-Spatial Content

    Not necessary for                                      Dallas
  “Feeling of Familiarity”
                                                             Texas
     Required for
   Associative
   Recognition/Recall

     Paired Associate
   Task: e.g. Table-
   Giraffe...... Table-?
      Role in binding
                              reviewed in Eichenbaum, 2004 Neuron
   together multiple
   elements of episode into
   memory trace
                                             Content                    How?
              Place
                                         Temporal Sequence




  Recent discovery of MEC Grid cells
                                                                Hafting et al, nature
   HC integrates parallel streams of spatial and non-spatial:          2005
information: CA3

  Spatial/Place representations in HC act as scaffold into
which other aspects of event (sequence, content) are
bound- forming episodic memory traces
                      CA3




Autoassociation




                  Pattern completion
                               Spatial Navigation
                            Autobiographical Memory
                             Associative recognition
                                 Free Recall
                    Tasks     “Perceptual” /STM
                              Trace conditioning
                             Transitive Inference
New Predictions                   Imagination




                                               Spatial
                   FORMAL
                                              Sequence
                    MODEL                    Associative



                                         Function of Upstream
         Anatomy                               Regions
    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...
  Thanks..
 EleanorMaguire
 Demis Hassabis

 Hugo Spiers

 Benedetto de Martino

								
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