Learning and memory Flashcards
What is learning and memory ?
Definition – broadly defined as a mechanism by which past experience alters present experiences or behaviours (Similar to cognition definition (once abstract thoughts taken away)
“once bitten twice shy” learned so you don’t do that again
What are Engrams?
The link between memory’s and remembering is presumed biochemical in nature: termed Engrams (Chemical or structural change in the brain which we think is responsible for memory and learning - not 100% sure yet)
No body actually knows with certainty where Engrams are or how they are formed
Early experiments showed that rats did not form specific pathways between sensory areas and motor areas (early engram idea)
His results showed that quite large areas of cerebral cortex had to be removed to prevent learning and memory of complex tasks and that these lesions had little effects on simple tasks.
The implication of these data are that memory and learning is performed using parallel processing systems and not serial processing systems.
Currently we think engrams are located all over the brain, but in places related to processing the learning (amygdala for fearful memories etc)
Memory and learning is an adaptive process and it doesn’t affect the ability to learn and memory (in rats, not proven in humans!)
What is Hebbian learning and networks associated with it?
Give rise to the adage that ‘cells that fire together, wire together’
As cells fire simultaneously they increase the synaptic associations. This results in networks of cells which are synaptically linked – associative learning
Pathway that fires again and again increase synapse associations (learning) so this pathway is the go to one to fire a signal
Associated networks - Habituation and sensitisation
What is Habituation ?
Habituation - decrease in response (& NT release) with repeated stimulus (E.g sitting down and feeling seat is cold then habituate and forget about the feeling)
What is Sensitisation ?
Sensitisation - Increase in response with repeated stimulation - mediated by an interneuron
Irritated - constantly poked but then get annoyed
What is long term potentiation ?
Long term potentiation (LTP) is path specific
- Stimulate pathway 1
with a single spike and
record - Stimulate pathwayl
with a train of spikes - re-stimulatewith a
single spike and measure
EPSP - Stimulate pathway B
with a single spike and
measure the EPSP - Enhanced response in
path 1 is long-lived and
specific to that pathway
Long term synaptic
changes requires genetic
involvement
By injecting current you get an action potential in cell
If you do stimuli then stop and do quickly again get an increased response (pathway 1)
LTP - increased response can increase for a long time once you’ve changed it (to do with genetic mobilisation and activating transcription factors which will release more receptors and neurotransmitters)
If synapses were only capable of LTP what would eventually happen?
To prevent ‘whole brain potentiation’ there is a reverse effected (called habituation)
What is Long Term Depression (LTD)?
LTD is initiated by a slower train of stimulatory impulses over a longer period
LTD can modulate LTP or even reverse it
What are the 3 different taxonomy of memory ?
Short term, long term and working memory
What is short term memory ?
Short term memory;
A very brief memory (seconds) either from an external stimulus or retrieval from a long term memory
Easily displaced by another stimulus
Can be extended into working memory by;
- Repetition in a phonic look (temporal extension) or
- Chunking which links familiar chunks together to extend the size of chunk
Phonic loop - repeating what you do “car keys, car key” going around in head to give a temporal extension of short term memory
How can we test Short Term memory?
Most commonly used clinical test is the digit span
Subject reads an increasing series of numbers which they immediately repeat
The number of digits that can be repeated back immediately is the digital span - usually around 6-7 digits is normal
If you already know several sequences, you can simply remember which sequences to recall - called ‘chunking’ & is used by chess masters
i.e 12 letters U,I,S,A,B,S,M,C,P,D,O,F are easy when ‘chunked’ into USA, IBM, SCO, PDF
What is Working memory ?
Working memory;
1). The maintenance and integration of information in an active state for. relatively brief time in order to achieve a short term task or goal
2). Is comprised of a mixture of short and/or retrieved long term memory
As short term memory only lasts a few seconds it must be repeatedly re-activated, its reactivation and subsequent duration is working memory (this is known as an executive function)
When the task is over, the working memory either is encoded into long term memory or is left to lapse
Note - it is also possible for LTM to be formed directly from sensory input under control of executive functions (pre-frontal cortex)
(E.g feeling or slamming fingers in car door )
Without executive function nothing else can happen
What are the features of long term memory (LTM) ?
Long term memory (LTM) is huge by comparison
Long term memory (LTM) - the acquisition and retrieval of information over long periods
It can be sub-divided into;
- Declarative memory (Can say what memory is and relate to other people)
- Non-declarative memory (That memory that allows you to do thing in autonomic nervous system and limbic and cerebellar (e.g ride bike)
What is the taxonomy of declarative memory ?
Image
What is the taxonomy of non-declarative memory ?
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What are the sub divisions of learning and memory?
The sub divisions of learning and memory are context dependent
Despite these different sub divisions, the process of learning (storing memory) is thought to be similar to all types and consists of 4 parts;
1). Encoding - memory creation
2). Storage - persistence of memory traces
3). Retrieval - memory recovery
4). Consolidation - strengthening of memory traces
What structures are associated with the formation of memory?
The structures associated with the formation of memory are in the temporal lobe system and are;
- Basal Forebrain
- Prefrontal cortex
- Mamillary body
- Thalamus
- Hippocampus
- Rhinal cortex
- Fornix
How is memory formed?
A series of events are encoded by the hippocampus, and a reference is made to their memory location - hippocampal index
If this information is recalled prior to consolidation the hippocampus performs retrieval from its index of events
After consolidation of the memory retrieval can be initiated directly from the sensory cortices (stimulates less hippocampus but more storage points)
How is memory formed?
A series of events are encoded by the hippocampus, and a reference is made to their memory location - hippocampal index
If this information is recalled prior to consolidation the hippocampus performs retrieval from its index of events
After consolidation of the memory retrieval can be initiated directly from the sensory cortices (stimulates less hippocampus but more storage points)
E.g smelling fish and chips and thinking of St Andrews beach
How can Long Term memory be used during counselling?
Plasticity in LTM is used during counselling for posts traumatic stress disorder
Patients new asked to re-live the events leading to PTSD then given an adrenergic beta receptor blocker (propanolol) which blocks re-consolidation of memory
How does consolidation of declarative memory occur ?
Consolidation is a result of physical changes at the synapse
Occurs in medial temporal lobes
Becomes less reliant on hippocampus
What structural changes occur at the synapse during consolidation?
LTM memory is associated with changes in connectivity in networks of neurons predominantly in the cortex
Four changes in morphology on dendritic spines have been associated with LTP
What structures are involved in Non-declerative memory consolidation?
Structures are involved in Non-declerative memory consolidation;
- Amygdala
- Caudate nucleus (tail + head)
- Putamen
- Cerebellum
Corpus striatum (part of basal ganglia) = caudate nucelus + putamen - thought to influence memories involving movement & procedural memory (e.g Olympic diving)
Cerebellum - influences fine motor learning including speech movements
What happened in the patient case HM?
Patient HM suffered from epileptic seizures following a bike accident
These increased in severity with time until he was getting up to 10 minor seizures (focal aware) per day and a major one (unsocial aware) every few days. The source was assumed to be medial temporal lobes.
At age 27 he was operated on by William Scoville and had an 8cm length of medial temporal lobe removed bilaterally (which included entorhinal cortex, amygdala and the anterior 2/3 of hippocampus)
The surgery alleviated his symptoms and there was no effect on perception, intelligence (reportedly improved) or personality (some loss of smell) his working memory however is normal
His memory loss took form of profound amnesia of 2 forms
1). He had some retrograde amnesia in that he had no recollection of some years before his operation (going backwards)
2). He had extreme anterograde amnesia (unable to form new memories going forwards) characterised by;
- An inability to remember the identity of people he had just met and
- An inability to remember numbers or events - e.g his own age (constantly surprised) or the death of his mother
So with HM the memory of distant events was conserved
His problem was therefore, an inability to consolidate new declarative long term memories
He learned some facts (president of USA) but never recognised his psychiatrists Brenda Milner
Interestingly his anterograde memory deficit was uniform across all declarative modalities (visual, auditory, r other) but his short term working memory was intact
He was still able to learn to learn and retain how to draw in a mirror – viewed as a skill and therefore non-declarative
HM’s case illustrated that declarative, non-declarative, short term and long term memory are not processed in the same place of by the same mechanism
(First day he went out of lines a lot, got bettr day 2 and day 3, learned skill he wouldn’t remember that he done but did improve skill! Hippocampus wasn’t needed)
What are the different types of amnesia ?
Amnesia occurring without any other deficits is known as dissociated amnesia
Retrograde amnesia - Don’t remember anything that happened say 6 months ago.
Anterograde amenseia - Cannot remember anything after trauma
The relative degrees of retrograde and anterograde amnesia can vary, so supporting the view that storage and retrieval of memories involve different processes
People don’t usually get one or the other, usually a blend of the 2, to do with retrieval or memory, consolidation and generating new ones
What was the case of patient NA?
Aged 21 whilst in armed forces a colleague accidentally thrust a miniature fencing foil up through NA’s nose and into the left dorsomedial thalamic nucleus. In addition his mamillary bodies were damaged bilaterally. The hippocampus was undamaged.
This patients cognition was normal and his IQ was unaffected. He suffered from some retrograde amnesia extending about 2 years prior to the accident but also profound anterograde amnesia
