Lecture 5: Hippocampus and Memory
Part 1 - Standard Model of the role of the
hippocampus in memory
• Focus on humans and human-relevant hippocampal functions (e.g. memory, over spatial
processing and ‘anxiety’ as often looked at in rodents)
• Hippocampus when studied in humans, can see a much more general device for storing
memories
o What types of memory does the hippocampus store? Where is the long-term
storage for memories in the brain? Is it in the hippocampus?
The neuropsychology of the human hippocampus
• What are the effects of damage to the hippocampus?
• Does this help us construct theories of the functional role of the hippocampus?
Standard Model of the role of the Hippocampus in Memory Commented [IM82]: Popular up until the 80s
Still used to give an overview of memory role in hippocampus
Patient HM - bilateral temporal lobe resection to treat intractable epilepsy (to remove epileptic foci
in temporal lobe)
o (Hippocampus, entorhinal and perirhinal cotices, amygdala were removed)
§ ERCx is a cortical area that acts as a gateway/interface between
hippocampus and neocortex
o Surgery resulted in a reduction of epileptic symptoms, but a profound and
permanent amnesia
§ Remains a surgical intervention option to remove epileptic focus from brain
in drug-resistant epilepsy
Symptoms of hippocampal amnesia
• Anterograde amnesia for episodic memories Commented [IM83]: Anterograde = after the insult; loss of
memories after brain insult
o E.g. Clive Wearing - densely amnesic since encephalitis in 1985
Commented [IM84]: Symptoms of someone with hippocampal
o No impairments in speech or intelligence; he has self-awareness and insight into his damage, but not pure hippocampal defect – other brain damage
condition
What is preserved in hippocampal memory syndrome?
• Short-term memory (e.g. repeating a number, hold a conversation)
• General intelligence and linguistic ability
• Procedural or motor learning (striatum)
• Conditioning
• Priming
(Milner et al. 1968) – Case study report of HM
• HM has undisturbed language comprehension and linguistic ability
• Procedural or motor learning (e.g. riding a bike, playing a musical instrument) preserved
o Types of learning that are strongly dissociated from hippocampal amnesia
, o Tested via Mirror Drawing Task. He learnt and retained the Mirror Drawing Task
(performance curve), but had no memory of learning it.
o Key brain area involved in procedural learning is striatum
• Conditioning (e.g. Pavlovian) learning is preserved
• Priming (i.e. one stimulus can affect the answer of the question to the following stimulus??)
Mirror drawing - a form of learning preserved in HM
• To observe how well motor learning was preserved in HM
• He learnt the mirror drawing task but had no memory of performing the task previously
A taxonomy of memory
The MTL (diencephalon) is necessary for forming declarative memories – something available for
conscious recall; can be declared
• Semantic - memories for facts (e.g. word meanings)
• Episodic - memories for specific events at a particular time and place
o Involve an element of mental time-travel; autobiographical memory
• Definition is based on some speech and language, thus declarative memory is difficult to
measure in rodents
Is the hippocampus even the long-term storage site, or is it just made in hippocampus and stored
elsewhere?
Is the hippocampus needed for memory encoding (making) or retrieval (storage)?
The importance of Retrograde Amnesia
• Anterograde amnesia is the core deficit in Hippocampal Memory Syndrome
o Anterograde amnesia alone doesn’t tell you if the problem lies with memory
formation or memory storage
• A problem with storage (after Hippocampal damage) should also produce retrograde Commented [IM85]: Memory before insult
amnesia
o Would also suspect resultant personality changes
• HM showed retrograde amnesia for events in his 20s but not from his childhood (temporal
profile of his retrograde amnesia)
o He has strong preserved semantic memory
o His childhood memory recall is akin to controls
Hippocampal damage brings on a quite interesting temporal pattern of graded memory loss
whereby, the longer ago something happened, the better you can remember it
The Standard Consolidation (SC) Model of Medial Temporal Lobe function
(Squire & Alvarez, 1995)
• The hippocampus is not the permanent storage site of memories
• The hippocampus is needed to make (and store) memories initially, and may be the
storage site for memories for a few years
o A slow process occurs whereby neural activity relating to memory stored in the MTL
produces changes in the networks of the neocortex
, • Key mechanistic point of this model: while the hippocampus has very fast-changing
connections (within hippocampus and cortical connections), neocortical changes
themselves are very slow
o To create a memory network in neocortex, one must train the neocortex based on
MTL data. But it takes years of practise and rehearsal (consolidation) to set up a
memory in neocortex independent of hippocampus (due to slow-changing intra-
cortical connections)
Apparently, as time passes after learning, there is a gradual reorganisation within long-term memory
storage whereby the importance of the hippocampal formation gradually diminishes and a more
permanent memory system develops that is independent of this region. This gradual process of
reorganisation is usually termed memory consolidation.
Consolidation occurs when the hippocampal system repeatedly reactivates representations in
neocortex, leading eventually to strong interconnections among cortical sites of the hippocampal
system.
• cortical connections are slow changing
• Hippocampal-cortical and intra-hippocampal connections are fast-changing
The MTL is not the storage site. The MTL ‘binds together’ neocortical memory traces. Overtime,
these become independent of the MTL.
Memories are initially stored in the hippocampus. Memories are made stronger via consolidation in
other areas of the brain (neocortex), where long-term storage occurs.
SUMMARY
HM(S?) —> severe anterograde amnesia for events and facts —> (1st part of Standard Model) MTL Commented [IM86]: Hippocampus and surrounding tissues
store declarative memories —> HM and similar patients don't have complete amnesia —> the
hippocampus isn’t an absolute, permanent storage site for all memory —> temporally graded
retrograde amnesia in HM —> (2nd part of Standard (Consolidation) Model) memories are initially
stored in hippocampus, then consolidated by being moved outside the hippocampus, probably to
other neocortical areas
Part 1 - Standard Model of the role of the
hippocampus in memory
• Focus on humans and human-relevant hippocampal functions (e.g. memory, over spatial
processing and ‘anxiety’ as often looked at in rodents)
• Hippocampus when studied in humans, can see a much more general device for storing
memories
o What types of memory does the hippocampus store? Where is the long-term
storage for memories in the brain? Is it in the hippocampus?
The neuropsychology of the human hippocampus
• What are the effects of damage to the hippocampus?
• Does this help us construct theories of the functional role of the hippocampus?
Standard Model of the role of the Hippocampus in Memory Commented [IM82]: Popular up until the 80s
Still used to give an overview of memory role in hippocampus
Patient HM - bilateral temporal lobe resection to treat intractable epilepsy (to remove epileptic foci
in temporal lobe)
o (Hippocampus, entorhinal and perirhinal cotices, amygdala were removed)
§ ERCx is a cortical area that acts as a gateway/interface between
hippocampus and neocortex
o Surgery resulted in a reduction of epileptic symptoms, but a profound and
permanent amnesia
§ Remains a surgical intervention option to remove epileptic focus from brain
in drug-resistant epilepsy
Symptoms of hippocampal amnesia
• Anterograde amnesia for episodic memories Commented [IM83]: Anterograde = after the insult; loss of
memories after brain insult
o E.g. Clive Wearing - densely amnesic since encephalitis in 1985
Commented [IM84]: Symptoms of someone with hippocampal
o No impairments in speech or intelligence; he has self-awareness and insight into his damage, but not pure hippocampal defect – other brain damage
condition
What is preserved in hippocampal memory syndrome?
• Short-term memory (e.g. repeating a number, hold a conversation)
• General intelligence and linguistic ability
• Procedural or motor learning (striatum)
• Conditioning
• Priming
(Milner et al. 1968) – Case study report of HM
• HM has undisturbed language comprehension and linguistic ability
• Procedural or motor learning (e.g. riding a bike, playing a musical instrument) preserved
o Types of learning that are strongly dissociated from hippocampal amnesia
, o Tested via Mirror Drawing Task. He learnt and retained the Mirror Drawing Task
(performance curve), but had no memory of learning it.
o Key brain area involved in procedural learning is striatum
• Conditioning (e.g. Pavlovian) learning is preserved
• Priming (i.e. one stimulus can affect the answer of the question to the following stimulus??)
Mirror drawing - a form of learning preserved in HM
• To observe how well motor learning was preserved in HM
• He learnt the mirror drawing task but had no memory of performing the task previously
A taxonomy of memory
The MTL (diencephalon) is necessary for forming declarative memories – something available for
conscious recall; can be declared
• Semantic - memories for facts (e.g. word meanings)
• Episodic - memories for specific events at a particular time and place
o Involve an element of mental time-travel; autobiographical memory
• Definition is based on some speech and language, thus declarative memory is difficult to
measure in rodents
Is the hippocampus even the long-term storage site, or is it just made in hippocampus and stored
elsewhere?
Is the hippocampus needed for memory encoding (making) or retrieval (storage)?
The importance of Retrograde Amnesia
• Anterograde amnesia is the core deficit in Hippocampal Memory Syndrome
o Anterograde amnesia alone doesn’t tell you if the problem lies with memory
formation or memory storage
• A problem with storage (after Hippocampal damage) should also produce retrograde Commented [IM85]: Memory before insult
amnesia
o Would also suspect resultant personality changes
• HM showed retrograde amnesia for events in his 20s but not from his childhood (temporal
profile of his retrograde amnesia)
o He has strong preserved semantic memory
o His childhood memory recall is akin to controls
Hippocampal damage brings on a quite interesting temporal pattern of graded memory loss
whereby, the longer ago something happened, the better you can remember it
The Standard Consolidation (SC) Model of Medial Temporal Lobe function
(Squire & Alvarez, 1995)
• The hippocampus is not the permanent storage site of memories
• The hippocampus is needed to make (and store) memories initially, and may be the
storage site for memories for a few years
o A slow process occurs whereby neural activity relating to memory stored in the MTL
produces changes in the networks of the neocortex
, • Key mechanistic point of this model: while the hippocampus has very fast-changing
connections (within hippocampus and cortical connections), neocortical changes
themselves are very slow
o To create a memory network in neocortex, one must train the neocortex based on
MTL data. But it takes years of practise and rehearsal (consolidation) to set up a
memory in neocortex independent of hippocampus (due to slow-changing intra-
cortical connections)
Apparently, as time passes after learning, there is a gradual reorganisation within long-term memory
storage whereby the importance of the hippocampal formation gradually diminishes and a more
permanent memory system develops that is independent of this region. This gradual process of
reorganisation is usually termed memory consolidation.
Consolidation occurs when the hippocampal system repeatedly reactivates representations in
neocortex, leading eventually to strong interconnections among cortical sites of the hippocampal
system.
• cortical connections are slow changing
• Hippocampal-cortical and intra-hippocampal connections are fast-changing
The MTL is not the storage site. The MTL ‘binds together’ neocortical memory traces. Overtime,
these become independent of the MTL.
Memories are initially stored in the hippocampus. Memories are made stronger via consolidation in
other areas of the brain (neocortex), where long-term storage occurs.
SUMMARY
HM(S?) —> severe anterograde amnesia for events and facts —> (1st part of Standard Model) MTL Commented [IM86]: Hippocampus and surrounding tissues
store declarative memories —> HM and similar patients don't have complete amnesia —> the
hippocampus isn’t an absolute, permanent storage site for all memory —> temporally graded
retrograde amnesia in HM —> (2nd part of Standard (Consolidation) Model) memories are initially
stored in hippocampus, then consolidated by being moved outside the hippocampus, probably to
other neocortical areas
