Learning and memory (plasticity) Flashcards
Memory is recall of learned information
Process by which information is processed, retained and recovered
Comes after learning
Neural changes/Location associated with storage/recall of information (after learning) is a memory trace/engram
Memory systems are classified by
Time - short-term and long-term
Nature – Declarative and Non declarative
Brain systems involved
Where is memory stored?
Pathologies, accidents, disorders in remembering, can provide clues about learning and memory
Types of memory
Short term: seconds to hours (working memory). Can be erased by shock or trauma
Long term: days to years. Not erased by head trauma
Explicit/Declarative:
Can be reported by an individual, conscious recall, easy to form and forget
Facts, events, people, places (Hippocampus, cerebral cortex)
Episodic: Life events It is very difficult to recreate these memories in other animals
Semantic: Memories of general information
Implicit/Non-declarative:
Cannot be called into conscious recall, tasks learned, tend to require repetition and practice
Perceptual and motor skills (cerebellum, striatum, amygdala)
How is memory formed?
Learning – Short term memory – Consolidation – Long term memory
*Not linear. Outcome of several processes.
*Specific memories are not stored in cells (neurons) but rather stored in form of the pattern of signals between cells.
*Starts with the acquisition of new information
*Short term memory (working memory), intermediate memory, consolidation and maintenance of long term memory. This involves transient modifications – ie amount of neurotransmitters released in response to signal, sensitivity of the post synaptic cells to the NTs
*Long term memory can involved permanent structural and functional changes between neurons
*Retrieval causes destabilization and re-stabilization of memories
*Updating and integration with other memories, so memories might change each time they are recalled
Glucosamine and LTP
1960’s: synaptic plasticity in glutamatergic pathways
Long term potentiation (LTP)
High frequency stimulation of glutamate neurones → long-lasting increase in efficiency of transmission
(see previous lectures and final slide in notes)
LTD – long term depression can also occur
Long term memory can involve changes in grey matter
Functional MRI can measure brain activity
fMRI studies have shown that the hippocampus (right) has a role in spatial memory
Study involving MRI scans of London taxi drivers found
*Posterior right hippocampus was larger in more experienced drivers
*Relative size of the hippocampus correlated with years of experience
London taxi drivers must use their spatial memory to navigate London. Years of such input is reflected in a physical increase in the right hippocampus gray matter volume
Where is memory stored in the brain?
Engram: Physical representation or location of a memory
Analysis of memory deficits after brain lesions (animals) or after disorders/accidents (humans)
can give us ideas where different kinds of memories might be stored
Maze learning in rats
Karl Lashley studied effect of brain lesions in rat on their ability to learn.
Rats trained through a maze for food reward
Before training: repeated mistakes
After training: went directly to the food
Brain lesions in association areas in the cortex made before training = rats needed more trials to learn to get to the food - lesions interfered with ability to learn
Brain lesions in cortex made after training = rats went down paths in the maze that they had previously learnt to avoid – lesions damaged the memory of how to reach food
Severity of defect correlated with the size, not location of the lesion
Speculated all regions of the cortex contributed to learning and memory
Conclusions incorrect: all regions of the cortex do not contribute equally to memory.
Memory studies in monkeys
Macaque monkeys can be trained to visually discriminate shapes
Particular shapes can be associated with food rewards
After training, lesions are made in a visual area in the inferior temporal lobe
The animals can no longer visually distinguish different shapes, ie cannot not remember the visual shape associated with the food reward even though vision is not affected.
Thus, memory for this task specific to vision is stored in a visual area in the cortex
However memory traces are present in multiple regions within the brain
Human case study: Henry Molaison
HM suffered from severe epilepsy
Seizure generating medial temporal regions (cortex, underlying amygdala and anterior 2/3rd of hippocampus) removed bilaterally by surgery
Surgery reduced seizures but affected declarative memory:
Long term memory formed before surgery intact (remembered childhood memories)
Short term memory okay (could remember list of numbers)
Procedural memory okay (could learn new skills)
Post-surgery he could not form new declarative memories:
lost the ability to encode new information about his experiences (episodic) or the world (semantic)
-> The hippocampus and median temporal lobes are required for formation and retention of memory
Structures in the median temporal lobes involved in declarative memories
Regions of the brain important for explicit memory (declarative memory) are
*the prefrontal cortex (mediates working memory)
*the hippocampus (stores declarative memory)
Ultimate storage site for declarative memory is the cerebral cortex
Object novelty recognition memory
Neural pathway of object recognition – a classic test for human memory defecit
Science direct:
“Object novelty recognition is derived from the spontaneous preference demonstrated towards an object which has not been encountered in the past. This preference of a novel object is the result of the retrieval of stored representations from previous experience of other objects.”
Connecting learning regions of the brain
Morris Water Maze – the rat tries to navigate unclear water to reach a platform – following cues it can learn the platforms location, one issue is that the rat will likely be highly stressed reducing memory ability and therefore potentially sqewing the data set.
Normal rats quickly learn where the platform is and swim to it
If there is bilateral hippocampal damage the mice cannot figure out how to find the platform
NMDA receptor is key for synaptic modifications in the hippocampus.
If the NMDA receptor is blocked by drugs injected into rats being trained in the water maze, the rats could not find the platform – first evidence that NMDA dependent processes have a role in memory.
( a paper in nature)
HOWEVER: could NMDA have a role in mediating stress instead?
NMDA blockers can reduce psychosis effects for example
3D all in one test
Can be used to measure motor, anxiety and memory
Most memories are disposed of aka ‘working memory’ processed in the prefrontal cortex
Cerebellum: memory processing - densest part of the brain (most neurons)
Hippocampus: memory processing – spacial, episodic (life events) etc.
(see diagram in notes for all brain areas involved in memory)
