Introduction to memory systems

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, pp115-126, 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

References

Hwang 2006

Hwang, 2006

Squire, 2004Attributes 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 amnesiaex: motor skillsex: word priming studies

Squire, 2004

Working MemoryDLPFC Parietal

(striatum=caudate+putamendiencephalon=thalamus and vicinity)

Squire, 2004

Multiple memory systems work independently and in parallel

Example: associated words in sentencesMedicine cured hiccups

Differently encoded in normals versus amnesics

* Structure and function go hand in hand in the memory 'System'

* Contrary to the psychological view which says there is one memory storage but different memory processes, neurobiology has clarified that there aremultiple memory 'systems'

BUT

Semantic memory

Thompson-Schill, 2003

Consistent activity during semantic processing:

A. Ventral Temporal CortexB. Prefrontal Cortex

MTL: MedialTemporal lobe

Martin and Chao, 2001

Filing clerk

Filing cabinet

How does semantic info get represented:1. Taxonomy: categorical specificity2. Attributes: sensory versus function

A. VENTRAL TEMPORAL CORTEX

Martin and Chao, 2001

Tasks producing theseactivations:* object-naming* picture matching* word-reading

1. Taxonomy: categorical specificity

1. Faces versus objects (or Animate/inanimate) organizationversusExpertise organization

The Haxby, Kanwisher, Gauthier debates

Controversies

The Clinton and Angelina Jolie neurons

Christoph Koch

Martin and Chao, 2001

2. Attributes: sensory versus function

Martin and Chao, 2001

Activity during:Mental imageryNaming tools > animalsViewing tools > animalsGenerating action words to toolsImagining tool manipulation

Activity during:viewing static objects that imply motion

Basic versus subordinate levels:For ex: human versus Marilyn MonroeTask: picture-word matching

Thompson-Schill, 2003

Visual attr:* color* size* motion

Function:* action IFG

IPCSTS (dynamic obj attrib)

ON periods: 3d rotating objects

Activity in primate brain: STS, OCC

M.E. Sereno et. al., 2002

Thompson-Schill, 2003

Thompson-Schill, 2003

B. PREFRONTAL CORTEX

LIFG = BROCA

Abstract 'objects'

No brain areas overlapped across studies

Bookheimer, 2002

Episodic memory

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 lateNot found in children younger than 4 years old(Give example from self)

Thompson-Schill, 2003

Tulving, 2002

Tulving, 2002

Brain bases for episodic memory

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 numberManipulation: mental map of an area when you ask for directions

Online manipulation of this type of information engages similar processesinvolved in reasoning, decison-making, problem solving, language understanding

There are separate WM systems for verbal and spatial information processing

Smith and Jonides, 1998

WM performance parameters:* Delay* Load

Processes:* selection* rehearsal

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

Curtis and D'esposito 2003

Curtis and D'esposito 2003

delayinterval

visualcuse response

task

Role of PFC from temporal storage perspective

Curtis and D'esposito 2003

Role of PFC from top-down control perspective

Role of PFC from action-perception perspective

Curtis and D'esposito 2003

Curtis and D'esposito 2003

Selection Rehearsal

Smith and Jonides, 1998

Curtis and D'esposito 2003

BROCA

Smith and Jonides, 1998

Storage POSTERIOR PARIETAL CORTEX

Smith and Jonides, 1998

Verbal working memory

activity in lefthemisphere

Localization: Control Task - Task: all L hemispherestorage = post parietal (BA40)rehearsal = Broca's (BA 44), pre-motor (BA6), SMA (BA 6)no executive processing

Task: respond Y or N ifthe probe letter is identicalin name to the previosly seen4 target letters

Control Task: respond Y or N ifthe probe letter is identicalin name to the previosly seen4 target letters (no memory requiredsince no delay)

no delay

Verbal working memory

Task:

Control Task1: Single target letter specified at thebeginning. Decide whether each given letter matches it.(subtract out perceptual processing)

Control Task2: Letter seen, press a button, rehearsethe letter, repeat. (subtract out rehearsal as well)

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

subtract

Smith and Jonides, 1998

Performance parameters: Load

N-back task, N=0,1,2,3

* Conduction aphasia (Wernicke's): Lesion in L posterior parietal area - subject cannot repeata word even immediately, when rehearsal is notneeded (L parietal = WM storage)

* Broca's aphasia: Lesion in L Broca's area - whenthere is significant delay, subject's forgetting curvedrops sharply.

rehearsal

storage

Spatial working memory

activity in righthemisphere

Task: respond Y or N if the probe position is identical to the previosly seen target spots

no delay

Control Task: respond Y or N if the probe position is identical to the previosly seen target spots

Localization: Control Task - Task: all R hemispherestorage = inf. post. parietal (BA40), ant. occipital (BA19) rehearsal = superior post. parietal, pre-motor (BA6)executive processes: Inferior frontal (BA47)

Rehearsal in spatial WM requires selectively attending totarget locations. In selective attention experiments, superiorpost. parietal and premotor areas activate.

Curtis and D'esposito 2003 Smith and Jonides, 1997

The top-down model

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 iscategory 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, FornixOutputs 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 post-synaptic neurons.

• Increased number of synapses that exist between pre- and 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 necessaryin encoding and retrieval processes only until memory is consolidated toneocortical destinations (2-3 years)

* In this model, memory traces are built bw hippocampus and neocorticaldestinations, 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 retrogradeamnesia

* MTT states that everytime a new autobiographical episodic memoryencoding occurs, a new memory trace is built regardless of whether ithas already been experienced. This strengthens the experiences by creatingmultiple traces.

* In MTT, traces from separate events may embody overlapping semantic information. Over time, neocortical representations of these overlappingsemantic information are created and act independently from the originalautobiographic memory trace for retrieval. However the original traces arestill preserved.

(Moscovitch, 2005)

Multiple trace theory (MTT)

(Moscovitch, 2005)

Task: Recollection of Autobiographical memory

In MTT, recollection and familiarity differ

Multiple trace theory (MTT)

(Moscovitch, 2005)

Task: Recollection of Autobiographical memory