Transcript Slide 1

Introduction to memory systems
References
1. L. Squire, Memory systems of the brain: A brief history and current perspective,
Neurobiology of Learning and Memory, Vol 82, pp. 171-177, 2004
2. J. D. E. Gabrieli, Cognitive Neuroscience of Human Memory, Annual Reviews
Psychology, Vol 49, pp.87-115, 1998
3. R. Cabeza, L Nyberg, Neural Bases of learning and memory: functional
neuroimaging evidence, Current opinion in neurology, Vol 13, pp. 415-421, 2000
4. Moscovitch et al. Functional Neuranatomy of remote episodic, semantic and
spatial memory: an account based on multiple trace theory, Journal of Anatomy,
Vol 207, pp 35-66, 2005
5. Martin A, Chao LL, Semantic memory and the brain: structure and processes,
Current Opinion in Neurobiology, Vol 11. pp.194-201, 2001
6. Thompson-Scill S, Neuroimaging studies of semantic memory: Inferring how
from where, Neuropsychologia, Vol 41, pp. 280-292, 2003
7. Tulving E, Episodic memory: from mind to brain, Annual Reviews of psychology,
Vol 53, pp 1-25, 2002
8. Hwang D, Golby A, The brain bases of episodic memory: insights from fMRI
intracranial eeg and patients with epilepsy, Epilepsy and behaviour, Vol 8, pp115126, 2006
9. Curtis C, Despozito M, Persistent activity in the prefrontal cortex during working
memory, Vol 7, pp 415-423, Trends in Cognitive Science, 2003
10. Smith E, Jonides J, Neuroimaging analyses of human working memory, PNAS,
Vol 95, pp 12061-12068, 1998
Hwang 2006
Hwang, 2006
Squire, 2004
Attributes of declarative memory
* representational
* remembered material can be compared and contrasted
* memories can be encoded in terms of relationships of multiple items and events
* stored representations are flexible
Attributes of non-declarative memory
* dispositional
* guided through performance
intact in amnesia
ex: motor skills
ex: word priming studies
Working
Memory
DLPFC
Parietal
(striatum=caudate+putamen
diencephalon=thalamus and vicinity)
Squire, 2004
Multiple memory systems work independently and in parallel
Example: associated words in sentences
Medicine cured hiccups
Differently encoded in normals versus amnesics
* Structure and function go hand
in hand in the memory 'System'
BUT
* Contrary to the psychological
view which says there is one
memory storage but different
memory processes, neurobiology
has clarified that there are
multiple memory 'systems'
Squire, 2004
Semantic memory
Consistent activity during semantic processing:
A. Ventral Temporal Cortex
B. Prefrontal Cortex
MTL: Medial
Temporal lobe
Thompson-Schill, 2003
A. VENTRAL TEMPORAL CORTEX
How does semantic info get represented:
1. Taxonomy: categorical specificity
2. Attributes: sensory versus function
Filing clerk
Filing cabinet
Martin and Chao, 2001
1. Taxonomy: categorical specificity
Tasks producing these
activations:
* object-naming
* picture matching
* word-reading
Martin and Chao, 2001
Controversies
1. Faces versus objects (or Animate/inanimate) organization
versus
Expertise organization
The Haxby, Kanwisher, Gauthier debates
The Clinton and Angelina Jolie neurons
Christoph Koch
2. Attributes: sensory versus function
Martin and Chao, 2001
Activity during:
Mental imagery
Naming tools > animals
Viewing tools > animals
Generating action words to tools
Imagining tool manipulation
Basic versus subordinate levels:
For ex: human versus Marilyn Monroe
Task: picture-word matching
Activity during:
viewing static objects
that imply motion
Martin and Chao, 2001
Visual attr:
* color
* size
* motion
Activity in primate brain:
STS, OCC
Function:
* action
IFG
IPC
STS
(dynamic
obj attrib)
M.E. Sereno et. al., 2002
Thompson-Schill, 2003
ON periods: 3d rotating objects
Thompson-Schill, 2003
B. PREFRONTAL CORTEX
LIFG = BROCA
Thompson-Schill, 2003
Abstract 'objects'
No brain areas overlapped across studies
Bookheimer, 2002
Episodic memory
Thompson-Schill, 2003
3 necessary components of episodic memory:
* subjective time
* autonoetic awareness
* time traveler
Episodic memory is about happenings
at particular places at particular times:
- what
- where
- when
Episodic memory develops late
Not found in children younger than 4 years old
(Give example from self)
Tulving, 2002
Brain bases for episodic memory
Tulving, 2002
Hwang, 2006
Working memory
Working memory
Defn.: Maintanence or manipulation of a limited amount of information
(1-10 items) in an active state for a brief amount of time (0-60 sec).
Ex: Maintanence: telephone number
Manipulation: mental map of an area when you ask for directions
Online manipulation of this type of information engages similar processes
involved in reasoning, decison-making, problem solving, language
understanding
There are separate WM systems for verbal and spatial information processing
Smith and Jonides, 1998
Modules/Components:
•storage (decays rapidly)
•rehearsal (can reactivate storage)
•executive processing (may be same in both verbal and spatial WM)
•For maintanence, only storage & rehearsal needed
•For manipulation, executive processing is also necessary
Processes:
* selection
* rehearsal
WM performance parameters:
* Delay
* Load
Curtis and D'esposito 2003
Role of PFC from temporal storage perspective
visual
cuse
delay
interval
response
task
Curtis and D'esposito 2003
Role of PFC from top-down control perspective
Curtis and D'esposito 2003
Role of PFC from action-perception perspective
Curtis and D'esposito 2003
Selection
Rehearsal
BROCA
Curtis and D'esposito 2003
Curtis and D'esposito 2003
Storage
POSTERIOR PARIETAL CORTEX
Smith and Jonides, 1998
Smith and Jonides, 1998
Verbal working memory
no delay
Task: respond Y or N if
the probe letter is identical
in name to the previosly seen
4 target letters
activity in left
hemisphere
Control Task: respond Y or N if
the probe letter is identical
in name to the previosly seen
4 target letters (no memory required
since no delay)
Localization: Control Task - Task: all L hemisphere
storage = post parietal (BA40)
rehearsal = Broca's (BA 44), pre-motor (BA6), SMA (BA 6)
no executive processing
Verbal working memory
Task:
Control Task1: Single target letter specified at the
beginning. Decide whether each given letter matches it.
(subtract out perceptual processing)
Control Task2: Letter seen, press a button, rehearse
the letter, repeat. (subtract out rehearsal as well)
subtract
Localization:
Control Task1 - Task: Verbal WM = L Broca's + L premotor + L post. parietal cortex
Control Task2 - Task: Reveals only storage = L post. parietal
Control Task2 - Control Task1: Reveals only rehearsal = SMA + Broca's
Control Task1 - Control Task2: Reveals just a little storage = L post. Parietal
Performance parameters: Load
* Conduction aphasia (Wernicke's): Lesion in L
posterior parietal area - subject cannot repeat
a word even immediately, when rehearsal is not
needed (L parietal = WM storage)
storage
* Broca's aphasia: Lesion in L Broca's area - when
there is significant delay, subject's forgetting curve
drops sharply.
rehearsal
N-back task, N=0,1,2,3
Smith and Jonides, 1998
Spatial working memory
no delay
Task: respond Y or N if the
probe position is identical to
the previosly seen target spots
Control Task: respond Y or N if
the probe position is identical to
the previosly seen target spots
Localization: Control Task - Task: all R hemisphere
storage = inf. post. parietal (BA40), ant. occipital (BA19)
rehearsal = superior post. parietal, pre-motor (BA6)
executive processes: Inferior frontal (BA47)
activity in right
hemisphere
Rehearsal in spatial WM requires selectively attending to
target locations. In selective attention experiments, superior
post. parietal and premotor areas activate.
The top-down model
Curtis and D'esposito 2003
Smith and Jonides, 1997
Overall
Cabeza, 2000
* How to study memory from this table & structures:
- Local approach: Relate each brain region to a process within cognitive domain
- Global approach: Associate each brain region an operation that is recruited
by a variety of tasks
- Network approach: Interpret the role of each brain region in relation to other
regions engaged by the same task
Neocortex is the ultimate repository for consolidated long-term memory, which is
category specific: name of objects, name of people, proper nouns, living things,
manufactured things (tools), food (fruits and veg.) (see N. Kanwisher)
The differential cortical geography of knowledge in healthy brain is still a mystery.
Last but not least:
Hippocampus and MTL Structures
Hwang 2006
Hippocampus and other players
Entorhinal cortex gets input from amygdala, all
association areas of cortex, Fornix
Outputs of hippocampus: from field CA1 and
subiculum to entorhinal and association cortex
Moscovitch, 2005
Fornix
• Several studies have shown
that damage to the fornix
causes anterograde
amnesia
– Amount of damage is
correlated to the severity of
symptoms
• Fornix:
– carries outflow of info from
hippocampal formation to
diencephalon
– carries axons into
hippocampus
• Amnesia can be caused by
interrupting either of these
processes.
Mammillary Bodies
• Mammillary bodies
are related with
Korsakoff’s syndrome.
• In patients with this
syndrome, there is
almost always severe
degeneration of
mammillary bodies.
• Therefore, shrinkage
of this region is
positively correlated
with memory deficits.
Moscovitch, 2005
!!!! wrong
Gabrieli, 1998
LTP, the long lasting
enhancement of synaptic
transmission , has long been
regarded, along with it's
counterpart LTD, as a potential
mechanism for memory formation
and learning.
Hebbian learning
• Learning depends on the pre and postsynaptic cells
being depolarized at the same time.
• “Neurons that fire together wire together”.
• A synapse that undergoes a long term change in
strength is called a Hebbian synapse
LTP
• similar to kind of change that was postulated by Hebb in
1949 to underlie memory
• In vitro, brief period of intense high frequency stimulation
(of perforant path) enhances the subsequent response of
postsynaptic neurons granule cells in dentate gyrus to
low-intensity stimulation of the presynaptic neuron. This
enhancement can last for weeks.
• LTP requires co-occurance of activation of pre- and postsynaptic neurons.
• Increased number of synapses that exist between preand post-synaptic neurons following induction of LTP
• Consolidation: Process which results in transfer of
information into LTM
Hwang 2006
• Two major types of amnesia include:
• Anterograde amnesia – the loss of the ability
to form new memory after the brain damage
occurred.
• Retrograde amnesia – the loss of memory
events prior to the occurrence of the brain
damage.
Multiple trace theory (MTT)
* Standart consolidation theory states that hippocampus is necessary
in encoding and retrieval processes only until memory is consolidated to
neocortical destinations (2-3 years)
* In this model, memory traces are built bw hippocampus and neocortical
destinations, and when consolidation is finished, the traces are pulled out
from hippocampus, stay localized to neocortex
* However this view is not supported fully by lesion literature in retrograde
amnesia
* MTT states that everytime a new autobiographical episodic memory
encoding occurs, a new memory trace is built regardless of whether it
has already been experienced. This strengthens the experiences by creating
multiple traces.
* In MTT, traces from separate events may embody overlapping semantic
information. Over time, neocortical representations of these overlapping
semantic information are created and act independently from the original
autobiographic memory trace for retrieval. However the original traces are
still preserved.
(Moscovitch, 2005)
Multiple trace theory (MTT)
Task: Recollection of Autobiographical memory
In MTT, recollection and familiarity differ
(Moscovitch, 2005)
Multiple trace theory (MTT)
Task: Recollection of Autobiographical memory
(Moscovitch, 2005)