Hippocampal memory and plasticity Flashcards
What are the two classification of memory?
temporal and declarative/non-declarative
What is learning?
Learning is a process by which new information is acquired by the nervous systemand gives rise to changes in behaviour
What is memory?
Memory: encoding, storage and retrieval of learnt information.
Anterograde amnesia
inability to form new memories
Retrograde amnesia:
inability to recall prior events and memories
How can memories be categorised based upon time?
Immediate memory (fractions of a second-seconds), working memory (seconds-minutes) and long-term memory (days-years)
What is meant by declarative memory?
(available to conscious) “what/where” memory
- storage and retrieval of information that is available to our consciousness and can largely be expressed by language
What is meant by non-declarative memory?
(generally not available to consciousness) “how to” memory
- often called ‘procedural memory’ that is often not availableto consciousness and covers many memory processes which are non-verbalise
What role does the hippocampus play in declarative memories?
- Clinical case studies: lesions/hippocampal damage
- fMRI navigation experiments
- MRI anatomical studies
- Hippocampal disease & memory function
- Lesion studies in rodents
- Neuronal activation during spatial navigation
Lesion studies into memory. Patient H.M.
Surgery for epilepsy (1953)most of his Medial Temporal Lobes bilaterallyremoved.
White line indicates anteriortemporal lobectomyWhite arrow shows posteriorhippocampus remaining.
–>
Severe anterograde amnesia: Could not make new long-term memories
Lesion studies into memory: Patient K.C
Horizontal plane MRI section showing damage to hippocampal and parahippocampal brain regions.
Procedural learning and memory are intact.
Anterograde and retrograde episodic memory (what/where/when) is severely impaired.
However, retrograde ‘semantic’ memory (general knowledge) is still intact.
The man with 30-sec-memory
Movie of British man with severe short-term memory problems from hippocampal damage caused by herpes infection
Lesion studies into memory: conclusion.
Hippocampal damage is selective for declarative memories, but leaves procedural memories intact.
fMRI studies & human hippocampal function
Navigation accuracy in the virtual town correlates with activation of the right hippocampus.
Modulation of human hippocampal volume
London taxi drivers have to pass a navigational memory test called ‘The Knowledge’to memorise pre-set routes in the city.
the longer time spent as taxi driver, the bigger the Posterior hippocampus.
Disease-damaged hippocampus & dementia
Fewer healthy neurons around plaques & tangles
Spatial learning & memory in rodents. How is it tested? And What can be concluded?
Morris Water Maze:Rodent must learn to find the submerged platform to get out of the water and stop swimming.
Animal uses external cues in the room to learn and later remember where the platform is.
–> Hippocampal lesions disrupt spatial memory
In vivo recordings of rodent hippocampus. What is it? and what can be concluded,
Record neuronal spiking activity from different neurons in hippocampus during a behavioural task.
–>Rodent hippocampus contains place cells (spatially-modulated neurons that fire in specific locations)
Where are long-term memories stored in the brain?
H.M. had anterograde but NOT retrograde amnesia.
So… he could recall earlier memories even though he couldn’t make new ones.
What is found? Lashley’s experiments in search of the engram
- Reduction in learnt information ∝cortical brain lesion size.
- Effect enhanced in more complex maze-memory tasks.
Reactivation of declarative memories in the cortex
Strong connectivity between hippocampus and other cortical brain regions
What different types of evidence show the role of the hippocampus in declarative memories?
•Lesions in patients
•fMRI and MRI data
•hippocampal disease.
-) Rodent hippocampal experiments support these findings: lesions in rats & spatial navigation, hippocampal ‘place cells’.
Where are long-term memories likely to be stored?
Long-term memories are likely stored outside the hippocampus, in directly connected cortical regions.
