Memory Flashcards
Declarative Memory - Encoding
Encoding is the process of establishing a memory
Features are remembered in the same brain sensory and motor areas involved in encoding.
Relationship among the events that bind them together as a single memory (“index”) is stored in the medial temporal lobe.
Declarative Memory - Storage
Memories are strengthened or “consolidated” during a storage phase.
Makes them long lasting and perhaps permanent.
Some memories may not be strengthened, resulting in forgetting
Declarative Memory - Retrieval (recent memories)
Retrieval is the process of recalling a memory
An internal or external cue is used to trigger voluntary or involuntary retrieval
In recent memories the cues act by accessing the index in medial temporal lobe
Temporal lobe serves to coordinate information in cortical regions
Declarative Memory - Retrieval (old memories)
Retrieval is the process of recalling a memory
An internal or external cue is used to trigger voluntary or involuntary retrieval
In remote or old memories the cue can access the cortical circuits directly.
Memories can be retrieved without access to medial temporal lobe
Role of Frontal Lobe in Declarative Memory
Frontal lobes play a role in the semantic and linguistic processing important for encoding and retrieval.
connecting information with existing knowledge.
Guide search and evaluate search results
Also play a role in working memory
Role of Parietal Lobe in Declarative Memory
Important for attentional processes
Directing attention appropriately for the encoding and retrieval of memories.
Anatomy of medial temporal lobe
Hippocampus
Parahippocampal cortex
Rhinal Cortex (Perirhinal / EntoRhinal)
Medial temporal lobe connectivity
The perirhinal and pararahippocampal corticies receive input from unimodal and polymodal associated areas in the cortex.
They project primarily to the entorhinal cortex
Entorhinal cortex in turn projects to the hippocampus.
Hippocampus is well positioned to integrate information from multiple cortical regions into a single memory or event.
Cognitive map theory (hippocampus)
Hippocampus plays a role in memory for the spatial relationship among items.
Existence of place cells in rodent and human hippocampus.
Experienced taxi drivers have larger hippocampi than controls – size correlates with years driving.
Relational memory (hippocampus)
Hippocampus plays a role in memory for the new associations – not just spatial ones.
Tested using odor associations in rodents.
Learns preferences in pairs of odors based on the presence of a reward.
A>B, B>C, C>D
Can later infer relationship across pairs
A>C
Lesions to hippocampus disrupt the ability to learn relationship across pairs.
Patient K.C.
Patient K.C. had lesion to hippocampus
impaired episodic memory – memory for personal events
Spared semantic memory – can remember and learn facts.
Hippocampus in episodic vs semantic memory
Hippocampus plays a role in episodic memory rather than semantic memory.
Episodic memory is related to recognition (reporting details).
Knowing is also related to semantic memory (no details).
Hippocampus activates only for recognition
Experimental paradigm from Ranganath et al., 2004
(hippocampus and enncoding)
Studied 360 items presented in different colors during fMRI scanning.
Participants responded by:
Rating whether they had seen the item before (1 new - 6 old)
Reporting the context the item was presented in (color)
fMRI categorized based on responses.
Correct and Incorrect.
Correct Source vs Incorrect Source.
Greater activity in Hippocampus and Parahippocampus for correct compared to incorrect source.
Familiarity based encoding
Now look at correlation between BOLD and confidence rating.
A measure of familiarity based recognition.
Found activity in entorhinal cortex.
Not in hippocampus.
Suggests dissociation between hippocampus and entorhinal cortex.
Hippocampus and Retrieval
Eldridge et al (2000) measured activity in hippocampus during memory recall.
Measured correct recall as well as remember compared to familiar.
Hippocampus was active only during correct recall and not when items were correct but only familiar.
Suggests supports a role for hippocampus in episodic recollection
False memories and context (Cabeza, 2001)
Cabeza, 2001 – had participants listen to related words,
Performed old/new recognition using old – new and false words.
False = same category as old – but not in old list.
Hippocampus did not distinguish between true (actual old words) and false words.
Parahippocampal gyrus was active only for true words.
Hippocampus active in response to the context and relationships of the words
Three process theories
Perirhinal cortex involved in memory for objects – input from ventral pathway.
Parahippocampal cortex encodes information relevant to spatial relationships – input from dorsal pathway.
Hippocampus Encodes the item (object) in its context (relationships).
Explains why perirhinal is related to familiarity and hippocampus to recollection. Helps to combine many of the previous theories we already discussed.
Sensory / Functional theory
Knowledge is remembered in the same brain sensory and motor areas involved in encoding.
Retrieving memories activates regions of the brain associated with the processing of the specific feature being recalled.
Action words – motor areas
Sound words – auditory areas
Cortical storage of memories
Applies even during passive viewing of words
Action words related to the face (Lick) activate the face area of the motor cortex.
Works like “Punch” activate arm area and “Kick” activate leg area.
Suggests that the representation of the meaning of these words is stored in functional regions associated with the semantics.
Reactivation of sensory regions in memory
During an encoding stage a word was paired with either an image or sound.
During encoding :
the visual condition activated visual cortex.
The auditory condition activated auditory cortex.
During retrieval only the word was presented and an old/new judgment.
fMRI showed recapitulation during recall in which:
Remembering auditory word reactivation the auditory cortex
Remembering visual words reactivated visual cortex.
Two models for abstract knowledge
Distributed only – abstract knowledge emerges from the concrete network
Distributed plus hub – there is a specialized regions for conceptual knowledge
Posterior parietal cortex in retrieval
fMRI studies show that dorsal parietal cortex is associated with familiarity and low-confidence.
Ventral regions are more strongly associated with recollection and high confidence recognition.
Interpreted in terms of the attention to memory theory.
Dorsal attention stream
top down attention
Memory search and evaluation process.
Ventral attention stream
Bottom up attention
Captured by strong memories and retrieval cues
Dorsal parietal regions
associated with a positive SME – more active when items are subsequently remembered.
Ventral parietal regions
associated with a negative SME – more active when items are subsequently forgotten.
Ventral parietal region associated with failed memory during encoding and successful recollection during retrieval.
Synaptic consolidation
Synaptic consolidation involves the synaptic level changes that allow for the persistence of a memory.
Takes minutes to hours
System consolidation
System consolidation involves large scale changes in memory circuits
Takes days to years.
Involves changes in the contribution of different brain regions to memory.
Hippocampal lesions
Standard theory of consolidation
Standard theory suggests that the memory connections are slowing transferred to the cortical from the hippocampus.
Damage to the hippocampus will not affect such memories but will affect recent memory.
Multiple trace theory of consolidation
Multiple trace theory suggest that multiple traces are created in the hippocampus as an episodic memory is recalled and encoded .
Partial disruption of hippocampus can still spare the memory.
Sleep and consolidation
Some argue that memory reactivation during sleep is important for consolidation.
Recordings from visual cortex and hippocampus during maze running in an awake animal showed that neurons fired in a specific sequence.
There was also coordination between visual cortex and hippocampus.
The same pattern and coordination was observed during sleep.
Suggests that the events were replayed during SWS.
Reversal in parietal lobe activity
Successful memory is associated with decreased activity during encoding and increased activity during recall.
According to attention to memory
Bottom up attention during encoding reflects influence of distraction and other events rather than top down focus on the information to be learned.
Bottom up attention during recall reflects successful capture of attention.
outward/inward attention and memory
Alternative have been suggested that include inward vs outward directing of attention.
Ventral parietal regions are related to inward direction of attention related to considering personal aspects of episodic memory.
Effective during retrieval
Ineffective during encoding because encoding requires outward direction of attention.
