8 The Remembering Brain Flashcards
STM
STM = memory for information currently “in mind”; limited capacity
in an active state - RAM of computer
LTM
LTM = stored information that need not be presently accessed or even consciously accessible; has virtually unlimited capacity
All information from minutes, hours, days and years ago is in LTM, unless it happens to be presently brought to mind (in which case it enters STM)
Hold about facts or events
Minutes hours days years ago
Resembles hard drive - able to access if need
why was WM term proposed
Term WM proposed as it captures better the idea that the information currently in mind is manipulated
what does STM give the impression of
Whereas STM gives the impression of a static/passive store (maintenance)
ranganath et al 2004
subsequent memory effects for F and R
ranganath et al 2004
subsequent memory effects for F and R
scan phase - size and animacy
post-scan - confidence and source judgement
scan phase
size rleated decision
animacy - living or non
post scan
confidence - the word appeared in encoding study – definitely new to definitely old
memory source judgement
when were researchers able to classify each word as familiar
Researchers were able to classify each word as familiar when pps recorded increased recognition judgements but lack of accurate source judgements
when were researchers able to classify each word as recollected
Recollected - source judgements reported accurately
familiarity
Familiarity-based recognition was predicted by activation in the perirhinal cortex
as recognition confidence increases so does perirhinal cortex activity
recollection
Recollection-based recognition was predicted by activation in the hippocampus
retrieval - MTL effects
New decision - hasn’t been encountered at encoding
Familiarity - recognised as being encountered but no further detail comes to mind about the previous encounter
Recollection - pps recall additional details from encoding episode in relation to these items - recall thoughts when encountered item at encoding or anything that is extra to the item itself - context
hippocampus
recollection-based recognition (but not familiarity) independently of the type of stimulus
Objects
Faces
Scenes
Activation of the hippocampus was maximal when pps were able to recall additional details about the previous encounter with these items
rest of MTL
The rest of the MTL =
Familiarity based recognition with a degree of material-specialisation
Rest of MTL
Familiarity based
Different structures of the MTL
Responded to stimulus familiarity for slightly different types of stimuli
The perirhinal cortex supported familiarity for objects
Entorhinal cortex supported familiarity for objects and faces
Parahippocampal cortex responded to familiarity for objects and scenes
Amygdala - part of MTL supported familiarity for faces
what does the perirhinal cortex support in familiarity
The perirhinal cortex supported familiarity for objects
what does the Entorhinal cortex support in familiarity
Entorhinal cortex supported familiarity for objects and faces
what does the parahippocampal Cortex support in familiarity
Parahippocampal cortex responded to familiarity for objects and scenes
what does the amygdala support in familiarity
Amygdala - part of MTL supported familiarity for faces
is there a crtitical role of MTL in recognition memory
yes
what does the mtl do
Support functional specialisation depending
on the type of memory experience
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
where is familiarity memory supported
Familiarity memory is supported by the rest of the MTL (the cortices).
what areas are affected in alzhimers
One of the first structures affected in Alzheimer’s is entorhinal cortex and the hippocampus. A lot of patients, therefore, at the first stages of the disease, have difficulty with recall and with spatial memory (i.e., navigating in well-known environments).
The remaining of the MTL cortical areas remain relatively normal, until later stages of the disease. We may, therefore, assume that familiarity memory can assist these patients in recognising familiar faces and places. This is very often reported by family members and carers of AD patients, especially in the early stages. Although, their memory lacks episodic detail (in other words recollection), they can recognise familiar places and faces.
what is consolidation
Consolidation = process that stabilises a memory over time after it is first acquired
After consolidation a memory is more amenable to forgetting, it becomes more stable
what are the 2 consolidation types
synaptic consolidation
system consolidation
what is synaptic consolidation
structural changes in the synaptic connections between neurons
faster
structural change at synapse
may take hours - days to complete
Encoding and learning
More likely to have an action potential firing from one to the next neuron
Denotes learning of information
what is system consolidation
gradual shift in memory from hippocampus to the cortex
slower
reorganistion of neural circuit
what are the two theories of sytem consolidation related to hippocampal function
a) Standard consolidation theory - Temporary role of hippocampus
• b) Multiple trace theory - Permanent role of the hippocampus
Standard consolidation theory - what is role of hippocampus
temporary role
multiple trace theory - what is role of hippocampus
permanent role of hippocampus
what is ribots 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
amnesia in HM
HM demonstrated anterograde amnesia- unable to register any new memories
Demonstrated a degree of temporal gradient in his retrograde amnesia consistent with ribots law
retrograde amnesia
Memories from 2 years prior - recent past - completely lost
Memory for about 10 years prior/ before the onset of amnesia were fragmented
Memories from ultimate past were not compromised - recall events from early childhood
Couldn’t recall events from more recent times
temporal gradient in amnesia - patient PZ
korsakoff syndrme
autobiography - 2 years prior to onset of amnesia 1981
unable to learn new paired associates - anterograde amnesia
remembered some famous people from 1930-40 but not later
Had a degree of retrograde amnesia that exhibited a temporal gradient very similar to one proposed by ribots law
Remember some events from past up to until the 40s but after this period and closer to time of onset of amnesia - impaired
More recent memories impaired more than remote memories
standard consolidation model hypothesis
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
what is role of hippocampus according to standard consolidation model
Hippocampus binds together different elements of an episode
Perceptual, affective, conceptual and other characteristics of an episode are represented in different areas of the neocortex
The role of the hippocampus is to link together these different elements of the episode that are represented in different regions of the neocortex
The hippocampus functions as the glue that holds together the different elements of the episode
standard consolidation model
Memory reactivation is the core mechanism of this phenomenon
Reactivation of the hippocampus memory trace is thought to lead to the reinstatement of patterns of neural activity in the cortex
This means that every time the same memory is retrieved the connection between the hippocampus and the neocortical areas are strengthened but so are the neocortical areas that represent the different elements to the episode
Such reactivation subsequently results in stabilisation and refinement of the cortical traces
The more were retrieving a memory the more likely that the cortical elements that represent the memory will be refined and stabilised
When this happens repeatedly the storage and recall become independent of the hippocampus and depends more on the connections in the neocortical areas that represent this episode
what is the core mechanism of system consolidation
memory reactivation is the core mechanism
what does reactivation lead to
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.
retrieval of nonconsolidated and consolidated memory
Any events contain different elements and they contain different sensory areas - represented in different neocortical areas
hippocampus links different elements into coherent episode
After the presentation of a retrieval cue the hippocampus plays a critical role in reactivating all the different elements of these episodes - the activity in the hippocampus directs our memory to the other elements to retrieving the other elements of the episode- this happens more before memory has been consolidated - early stages of existence of memory
after memory is fully consolidated the connections with hippocampus become unnecessary and memory is reactivated using links created among the different neocortical areas that make up the specific event
In this case the memory has moved away from the links provided by hippocampus and is sustained by the cortical areas
semantic dementia damage to where
Semantic dementia - damage to anterior temporal lobes (cortex)
alzheimers disease - damage to where
Alzheimer’s disease – damage to
hippocampus and related structures
what happens in semantic dementia patients
SD patients can remember recent but not old events because memories not yet completely dependent on cortex – yet to be transferred out of hippocampus
alzheimers disease - what happens
In Alzheimer’s disease access to remote memories follow the temporal gradient dictated by ribots law
More recent memories effected more - less accessible than remote memories
Consistent with the standad consolidation theory - recent memories rely on integrity of hippocampus. - haven’t been consolidated yet
Remote memories consolidated into neocortical areas- more preserved
what happens in semantic dementia
In semantic dementia - access to more recent memories was more successful than access to remote memories
Recent memories still rely on the integrity of hippocampus which in this group remains in tact from atrophy whereas the rest of the neocortical areas have suffered from various degrees of atrophy
what is the double dissociation
Double dissociation of the effect of the temporal gradient after hippocampal vs non-hippocampal damage
Supports the basic premises of the standard consolidation theory
evidence for consolidation from amnesia
To explain retrograde memory loss, we assume that old memories are not fully consolidated at the time of injury.
Memories from ultimate past - consolidated away from the hippocampus and are represented in other neocortical areas do not suffer
More recent memories suffer due to hippocampal damage - closer to the onset of amnesia a memory is the more susceptible it will be
Temporal gradient of retrograde amnesia
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 - fmri of remote personal events
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
in multiple trace theory what is system consolidation
System consolidation should be thought of as transforming memories (from episodic-like
to semantic-like) not as transferring memories (proposed by standard model)
• Older memories become more semantic-like e.g., stories without episodic detail
• After hippocampal damage older memories can be successfully retrieved but in many
cases lack episodic detail (they are recalled like stories)
• Standard consolidation and multiple trace theory are still debated
standard theory of system consolidation
Memory relies on integrity of hippocampus early in its life
Hippocampus links together different neocortical elements of memory
Important in indexing location of elements
Later on with repeated exposure to specific repeated reactivations of these memories
The strength of a connection among the neocortical elements are strengthened while the connections to hippocampus are weakened
Passage of time and repeated reactivations - independent from hippocampus
multiple trace theory
Discriminates between context free or semantic like memories and contextually rich or episodic memories
According to them the standard theory of consolidation explains very well the transfer of episodic memories in the semantic state where contextual details are eliminated - semantic context-free memories
On the other hand contextually rich memories - episodic memories always rely on the hippocampus independent on passage of time
the water maze task
The water maze task
Hippocampal-lesioned rats fail to learn the location of the platform (and subsequently find it). On the other hand, rats with cortical damage perform like controls (without brain lesion): can still learn and remember the platform’s location. Therefore, the hippocampus is critical for learning and retaining spatial information!
Hippocampus supports spatial learning
food storing birds - hippocampus and spatial memory
Food-storing birds that rely on storing and then locating food have hippocampi about twice as large than non-food- storing birds
hippocampus
Hippocampus - binding together context and item information
Providing support in recollection
Important role in spatial memory
Representing and retrieving spatial information in the environment
london taxi drivers
Taxi drivers
Posterior hippocampus - consistently larger in taxi drivers than healthy controls
Size of posterior hippocampus significantly correlated with time spent as taxi drivers
Evidence hippocampus has prominent role in spatial memory
what are place cells
Neurons mapping locations within an environment. Each neuron represents one location (i.e., its place field).
Appear to be sensitive to the location of experimental animal in a 2-d environment
Each neuron or cluster of neurons appears to represent a single location as the mouse goes around exploring its environment there is activation in different neurons which presumably represent these specific locations
what are grid cells
Grid cells: Neurons in entorhinal cortex (EC) mapping multiple locations in 2-dimensional environments
Entorhinal cortex- main cortical area providing input to hippocampus
Represent multiple locations within environment
Sketch or grid of the surrounding environment
what are boundary/border cells
Boundary/border cells: Neurons in EC activating when the animal is near the borders of the environment
borders on the 2d environment
what do the MTL structures form
The MTL structures form a loop of information processing that supports encoding and retrieval
what are the two types of recognition memory
Recognition memory is generally believed to have two components: recollection (context-dependent) and familiarity (context-independent)
are the MTL structures are differentially specialised in supporting
familiarity and recollection
yes
what 3 types of memory rely on the hippocampus
Relational memory, context-dependent memory or recollection rely on the hippocampus
which areas play a role in familiarity memory
The surrounding cortical regions (perirhinal, entorhinal and parahippocampal cortex) appear to have a role in familiarity memory but their contribution may vary depending on the type of stimulus
standard consolidation theory
Hippocampus has a time-limited role in consolidation that gives rise to a temporal gradient when damaged (remote memories are spared more than recent memories)
multiple-trace theory
multiple-trace theory stresses the permanent role of hippocampus in remote memories especially when they retain their episodic vividness
