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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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