Learning and Memory Flashcards
What are the 2 types of memory?
Learning: acquisition of new information
Memory: retention of learned information
Two types of memory:
Declarative memory (explicit)
- E.g. facts and events, you can verbalise it – utilises the hippocampus
Nondeclarative memory (implicit)
- E.g. procedural memory—motor skills, habits - utilises the striatum
What are the 3 types of declarative memory?
Working memory
- Temporary storage, lasting seconds
- Easily accessible
Short-term memories—vulnerable to disruption
- Facts and events stored in short-term memory
- Subset are converted to long-term memories.
Long-term memories
- Recalled months or years later
What is memory consolidation?
Memory consolidation; process of converting short to long-term memories
Sensory information is going into the brain and becoming working and/or short term memory
Over time these memories are consolidated and become long-term
What are the functions of the pre-frontal cortex?
Prefrontal cortex and working memory
Primates have a large frontal lobe.
Functions of prefrontal cortex: self-awareness, capacity for planning and problem solving
So if we are trying to solve a problem we utilise the working memory which is beneficial
What are the other regions of the brain involved with working memory?
Other brain regions are involved, for example lateral intraparietal cortex neuron response in delayed-saccade task
The intraparietal cortex is located towards the back of the brain
Saccades are rapid eye movements
A monkey can retrieve a food rewards when they can look from the fixation point to where the target flashed after the fixation point disappears
Again the greatest spike of these neurons are during the delay period
Where are memories stored?
In general terms, they can be stored throughout the brain
In neuronal terms they are stored in the engram, groups of neurons that encode memories
First postulated in Hebb’s Cell Assembly and Memory Storage
He theorised that neurons exist in a network and when exposed to an external stimuli, activation continues even after the stimulus is removed as a sort of reverberation
Hebbian modification strengthens the reciprocal connection between neurons that are active at the time
The strengthened connections of the cell assembly contain the engram for the stimulus so when presented with an incomplete stimulus the neurons are still activated
How does information flow through the medial temporal lobe?
Sensory information will first go into the cortical association areas
It will then be funnelled through the areas that sit close to the hippocampus; the parahippocampal and rhinal cortical areas
Finally they feed into the hippocampus where there is some opportunity for feedback from the hippocampus to the cortical association areas
Things don’t just stay in the hippocampus, otherwise it would get full over a while
Information is filtered out via the fornix to other areas such as the thalamus and hypothalamus
The thalamus is like a sorting system that decides where certain information goes
What is amnesia?
Amnesia: serious loss of memory and/or ability to learn
Causes: concussion, chronic alcoholism, encephalitis, brain tumor, stroke
Retrograde amnesia- Inability to recall consolidated memories from a period before the time of trauma
Anterograde amnesia- Inability to form/ consolidate memories after the time of trauma
What are place cells?
Learning Morris water maze requires hippocampus
Place cells within the hippocampus fire when animal is in a specific place.
Place cells are dynamic, it takes habituating to a certain area before the place cells start firing and even then only certain ones will fire
What are the two models of memory consolidation?
Standard model of memory consolidation
- Information from neocortex areas associated with sensory systems sent to medial temporal lobe for processing
- Synaptic consolidation, systems consolidation
- Post consolidation, hippocampus not necessary
Multiple trace model of consolidation
- Hippocampal involvement is continued
- Multiple memory traces
Dependent upon synaptic plasticity – ‘the biological process by which specific patterns of synaptic activity result in changes in synaptic strength’
What is the model of distributed memory?
Rather than one neurons holding information that correlates to a specific memory, its actually distributes across neuronal populations
And dependent upon whether the subject is exposed to any one of these stimuli, you get a differential change in activity across more than one neuron
What is the trisynaptic’s link with synaptic plasticity?
The changes in neuronal response can be explained by synaptic plasticity.
The trisynaptic circuit of the hippocampus is often used in studies of this phenomenon
Trisynaptic circuit:
Information flows from entorhinal cortex, via performant path to the dentate gyrus
Mossy fibres originate from dentate gyrus and synapse upon pyramidal neurons in CA3 hippocampal region
Axons from CA3 (Schaffer collaterals) synapse upon pyramidal neurons in CA1 hippocampal region
If we increased the frequency of stimulation what you find is that the magnitude of the EPSP greatly increased
This magnitude in response is long-term potentiation
That is what synaptic plasticity is- if you continue to stimulate neurons at a high frequency you will get increased responsivity
What are the mechanisms of LTP in CA1?
Glutamate receptors mediate excitatory synaptic transmission.
NMDA receptors and AMPA receptors in respect to LTP
If you stimulate frequently enough and get release of high glutamate you get significant activation of AMPA receptors which leads to a significant activation of NMDA receptors
You get a big flood of calcium in, and therefore calcium calmodulin kinases which have a number of effects
One is to increase phosphorylation of AMPA receptors increasing responsivity
The second is increased expression of receptors in the post-synaptic membrane
This is partly what underlies LTP
What structural changes follow LTP?
Structural changes following LTP include dendritic spine growth
This is partly due to the increase of receptors to accommodate them
