Week 11 Lecture 11 - the remembering brain 1 Flashcards
What is a function - structure relationship of memory?
each function of memory corresponds to a different part of the brain
What are some issues with a function-structure relationship of memory?
- function and structure do not match
exactly - A structure can participate in multiple
functions - A function may rely on multiple structures
How can definitions of episodic memory vary depending on the criteria emphasised?
- Mental time travel: Tulving’s definition
emphasised the first-person ”mental time
travel” – emphasis on re-experience - Links: Ability to create links between
unrelated bits of information, making a
coherent episode – emphasis on relational
memory - Time and Place: placing a past experience within a particular time and place- emphasis on context
What is episodic memory the result of?
associative learning
- The what, where, when and who of an episode (its context) are associated and bound together
- They can then be retrieved (and
reexperienced) as a single episode
What is autobiographical memory?
- Personal memory
- Evens from personal past (like EM)
- Semantic personal past (facts about oneself e.g., address
What does the hippocampus include?
- Dentate gyrus
- Cornu Ammonis (CA) subfields
(CA1, CA2, CA3, CA4) - Subiculum
How is the medial temporal lobe (MTL) organised?
- hierarchical organisation
How does information flow within the MTL?
- information is initially collected through the perirhinal and parahippocampal cortices
- Then passes to the entorhinal cortex, and ultimately reaches the hippocampus
- The cortical regions, however, do not merely funnel information to the hippocampus
- A large network of connections both within and among the subregions of the MTL cortical regions perform extensive information processing
What is anterograde amnesia?
difficulties in acquiring new memories after onset of amnesia
What is retrograde amnesia?
difficulties in remembering events from just before the brain injury
What is the history of patient HM?
- Suffered from severe, intractable epilepsy
- Foci in both medial temporal lobes
- Treated with bilateral medial temporal
lobectomy - Included removal of the hippocampus and amygdala
After HM’s surgery, what good and bad things occurred?
o The Good:
* Reduced convulsions (severity and frequency)
* Improved IQ (from 104 to 118)
o The Bad:
* Minor retrograde amnesia (for events within the 2 years preceding the surgery)
o And the Ugly:
* Profound anterograde amnesia: could not form long-term memories for events after surgery
What was HM’s anterograde amnesia like?
*Preserved memory of the past, and had
good short-term/working memory
* Could not form new long-term memories
* Global amnesia: affecting all sensory
modalities
* Problems were limited to declarative/ explicit memory
On a digit span test, what is a normal ppts results? What was HM’s results?
- Normal subjects __> up to 18 digits
- After 25 trials of this task, H.M. still could not successfully repeat more than 7 digits –> could not turn STM to LTM
given an example of a task on which HM improved
- mirror drawing task
- Explicit (declarative) vs Implicit
(non-declarative) memory
What is the subsequent memory paradigm?
Aims to evaluate encoding-phase activity leading to successful (versus unsuccessful memory)
Wagner et al. 1998 studied Remembered vs Forgotten stimuli
What was the RQ?
Does the brain activity at encoding predict which items are later going to be
recognized and which will be forgotten?
Wagner et al. 1998 studied Remembered vs Forgotten stimuli
What was found?
Activity in the left ventrolateral
PFC (a) and the left MTL (b) was
predictive of later remembered
versus forgotten stimuli
What is familiarity?
sense of memory that a stimulus has been
encountered before
What is recollection?
memory for the context or other associative information about a previous encounter with a stimulus
What did a model by Eichenbaum et al. (2007) propose (memory)?
- The perirhinal cortex processes
item representations (important for
familiarity) - the parahippocampal cortex is
assumed to process “context”
(including scene perception) - The hippocampus binds items in
context (important for recollection).
Ranganath et al. (2004) studied Subsequent memory effects for
Familiarity and Recollection
What was found?
Familiarity-based recognition was
predicted by activation in the perirhinal cortex
Recollection-based recognition was predicted by activation in the hippocampus
What is the hippocampus responsible for?
The hippocampus is responsible for
encoding and retrieving the constituent
elements of an experience
For example:
* Names with faces
* Location of objects/people within a scene
What is familiarity memory supported by?
the MTL (not including hippocampus)
What is consolidation?
process that stabilises a memory over time after it is first acquired
What are the 2 types of consolidation?
- synaptic
- system
What is synaptic consolidation?
Structural changes in the synaptic
connections between neurons
May take hours – days to complete
What is system consolidation?
Gradual shift of memory from
hippocampus to the cortex
What are 2 theories of system consolidation (related to hippocampal function)?
- a) Standard consolidation theory –> Temporary role of hippocampus
- b) Multiple trace theory –> Permanent role of the hippocampus
What is Ribot’s law?
- Memory loss following brain damage has a temporal gradient
- More recent memories are more likely to be lost than remote memories
- Explanation is that remote memories have undergone systems consolidation
– they do not rely upon the MTL anymore, but are cortex-dependent
What was anterograde and retrograde amnesia like in HM?
see summary sheet
What was patient PZ?
- A university professor who had Korsakoff’s syndrome at the age of 65.
- Has written hundreds of research papers, book chapters etc.
- Has completed an autobiography 2 years prior to the onset of his amnesia (in 1981).
- Unable to learn new paired associates.
- Remembered some famous people from the 1930-1940 but not later.
What is the standard consolidation model?
- The hippocampus links together different kinds of information in many regions of brain (perceptual, affective, conceptual etc.)
- Hypothesis: Initially, hippocampus plays an active role in ‘binding’ the activity of
disparate cortical ‘modules’ - Over time, the hippocampus plays less of a role
How is memory reactivation involved in system consolidation?
- Memory reactivation is the core
mechanism. - Reactivation leads to the reinstatement of patterns of neural activity in the cortex.
- Such reactivation subsequently results in
stabilisation and refinement of cortical
traces. - This iterative process leads to storage
and recall becoming completely
dependent on the cortex, and
independent of the hippocampus.
Explain retrieval of nonconsolidated and consolidated memory
- An event with audio (A), spatial (S), and visual (V) information is encoded
- The hippocampus contains a unified representation of the event
- When a retrieval cue containing only spatial and visual information of the event is encountered before consolidation the
hippocampus plays a critical role - After the memory is fully consolidated, the connections with the hippocampus become unnecessary
- The retrieval cue accesses the memory directly from the cortical network of connections that form the unified
representation of the memory
Where is the damage in semantic dementia?
anterior temporal lobes
Where is the damage in Alzheimer’s disease?
hippocampus and related structures
What can semantic dementia patients remember? WHY?
SD patients can remember recent but not
old events because memories not yet
completely dependent on cortex – yet to be transferred out of hippocampus
to explain retrograde memory loss, what do we assume?
we assume that old memories are not
fully consolidated at the time of injury.
Proposed by Nadel and Moscovitch (1997,1998), what is multiple trace theory?
- The hippocampus never ceases to have important role in episodic memory recall
- Older memories have been reactivated many times over the years
- Each reactivation creates new traces in the MTL and in other neocortical structures
- To the extent that damage is not global, older memories are more likely to be remembered as they have multiple traces
Gilboa et al. (2004) investigated fMRI of remote personal memories
What was the method?
- Family members of participants
provided pictures of autobiographical
events - From remote past to more recent times
(5 photographs for 5 periods) - Participants scanned while thinking
about the event depicted and rating
vividness
Gilboa et al. (2004) investigated fMRI of remote personal memories
What was found?
- Hippocampus activated for both recent and remote memories
- Hippocampal activation was related to the richness of re-experiencing (vividness) rather than the age of the memory per se
Summarise standard theory and multiple trace theory
see summary sheet
