20 - Episodic Memory II Flashcards
Describe the multiple trace theory of long-term memory consolidation
Hippocampal complex automatically encodes all aspects of experience, represented at different neuronal sites, the whole episode is bound into a memory trace
Re-activation of the memory in a different neuronal and experiential context leads to new memory trace, traces share some or all of the information about initial episode
Multiple traces facilitate extraction of factual information common to all, which becomes independent of episodic context.
Older memories have more traces, so are more resistant to damage. Episodic context continues to be dependent on the hippocampal complex for as long as the memory trace is viable.
In the multiple trace model, what type of memories exhibit a temporal gradient?
Semantic information have a temporal gradient (i.e. facts)
Autobiographical episodic memories have no temporal gradient
What did imaging studies demonstrate about the multiple trace model?
Ryan et al (2001) found no difference in patterns of hippocampal activation for recent (<4 years) and remote (> 20 years) memories.
Age of memory didn’t change activity in hippocampus
Gilboa et al (2004) found that hippocampal activity was correlated with the vividness of re-experiencing the memory, rather than the age of memory
What structures are involved in the diencephalon-MTL system?
Thalamus, hypothalamus, mamillary bodies
There are two systems in the diencephalon-MTL system, describe each
- Extended Hippocampal-Diencephalic System
- connects hypothalamus to anterior thalamic nuclei
- hipp. -> thalamus and mammillary bodies via fornix.
- anterior thalamus -> hippocampus via cingulum bundle
- TIGHTLY CONNECTED - Perirhinal-Diencephalic System
- perirhinal cortex to medial dorsal thalamus. Directly and indirectly through entorhinal cortex.
- both project to prefrontal cortex
What did Aggleton and Brown suggest each of the diencephalon-MTL systems are used for?
The extended hippocampal-diencephalic system is involved in efficient encoding, so normal RECOLLECTION of episodic memories
Perirhinal-diencaphalic system is involved in familiarity-based item recognition
Describe the symptoms and causes of diencaphalic amnesia
Due to thiamine (B1) deficiency in alcoholism
Caused by damage to the diencephalon (dorsomedial and anterior nuclei of thalamus , mammillary bodies and often atrophy of prefrontal lobe)
Profound amnesia
- retrograde, severe anterograde and confabulation
What is the retrosplenial cortex comprised of and what does it anatomically connect to?
Comprises Brodmann areas 29 and 30
Strong connections to a range of memory structures (hippocampus and anterior thalamic nucleus)
What do lesions to the retrosplenial cortex result in, in humans and animals?
Impair spatial memory and navigation.
In humans, severe impairments in episodic memory and spatial disorientation
In rats, also impairments in contextual fear conditioning, compound-feature negative-discrimination tasks and active avoidance in two-way shuttle box
What is the retrosplenial cortex’s main role in spatial memory?
may play a “translational” role between allocentric and egocentric spatial reference frames.
- Orientation of self in space
- Situating self in a recollected memory episode, “seeing” it from a particular viewpoint
What is the first site of hypometabolism in patients with amnestic mild cognitive impairment?
Retrosplenial cortex
A prodrome to Alzheimer’s disease
What are the structures associated with the core network in autobiographical memory?
- Medial and lateral temporal lobes
- Medial and ventro-lateral frontal lobes
Retrosplenial/posterior cingulate cortex - Temporo-parieto-occipital junction
What is the default mode network?
A distributed network of regions that are more metabolically active when a person is “at rest” compared to when they are engaged in a task.
Corresponds to distribution of amyloid plaques
What is the relationship between the core network and the default mode network?
- High degree of overlap of default mode with the “core network”
Medial prefrontal cortex
Medial parietal cortex (posterior cingulate/precuneus/RSC)
Inferior parietal lobe (angular gyrus)
Medial and lateral temporal lobe
How does the core network respond to imagining future events?
Areas in the core network activate
