Week 6: Memory systems Flashcards
What is learning?
The process of acquiring new information
What is memory?
Learning that is actually stored and retrieved
What are the 3 stages of learning and memory?
Encoding
Storage
Retrieval
What happens in the encoding stage?
We process incoming information
Acquisition: registration and analysis of sensory input
Consolidation: creating a stronger representation over time
What happens in the storage stage?
Permanent representation of the information is formed and stored
What happens in the retrieval stage?
Stored information is retrieved back into conscious awareness
What is the capacity of short-term and working memory?
Limited capacity
7 +/- 2
Can try and increase Capacity by chunking etc
What is visual information called? and how long does it last?
Iconic
300-500 milliseconds
What is auditory information called? And how long does it last?
Echoic
9-10 seconds
What can long term memory be divided into?
Declarative (explicit - we can explicitly recall and have conscious access)
Non-declarative (Previous experience may facilitate a response but we don’t necessarily have a conscious recollection)
What can declarative (explicit) memory be divided into?
Events/episodes (episodic)
Facts (semantic)
What can non-declarative (implicit) memory be divided into?
Procedural (skills)
Perceptual representation system (perceptual priming to respond in a particular way)
Classical conditioning (responses between 2 stimuli)
Non-associative learning (habituation, sensitisation)
What does the medial temporal lobe include?
The hippocampus, parahippocampal, entorhinal and perirhinal cortices
What does damage to the medial temporal lobe result in?
Severe amnesia
What connects the hippocampus to other subcortical structures?
The fornix
What connects the hippocampus to the cortex
Entorhinal cortex and fornix
What other subcortical structures are important for memory?
- Anterior thalamic nuclei
- Mammillary bodies
- Amygdala (tagging emotional content to memories)
Where is the hippocampus located?
Located in the temporal lobe of each hemisphere
What structures are a part of the hippocampal formation
- Parahippocampal gyrus (adjacent cortex)
- Dentate Gyrus (Strip of gray matter between the 2)
- Entorhinal cortex & Subiculum (both involved in the flow of information through the hippocampus)
What is the hippocampal formation divided into?
Divided into 4 regions CA1-CA4 (CA = cornu amonis)
How does the hippocampus receive information from the rest of the cerebral cortex?
Via the perforant pathway
What is the perforant pathway?
Starts in entorhinal cortex and projects to the dentate gyrus
Fibres then leave the dentate gyrus to the CA3 region
Neurons in CA3 region send axons to neurons in CA1
Then projected to the neurons in subiculum
Travels back to entorhinal cortex and then out
How is the prefrontal cortex involved in memory?
Involved in retrieval and storage - damage here leads to problems in episodic memory particularly regarding the order of events
Dorsolateral prefrontal cortex and memory?
Important for working memory processes - manipulating information
What role does the inferotemporal play in memory?
Storage of visual representations
What structures mediate implicit memory?
Sensory motor circuits
- cerebellum and striatum
Cerebellum and implicit memory?
Important for sensory motor skill learning and pavlovian conditioning
Striatum and implicit memory?
Important for habit formation
Explain Atkinson & Shriffrin’s Modal model of memory
Have sensory information that comes into the information processing system and is first stored in a sensory register
Items are then selected via attention and moved into short term storage (STM) and then if we rehearse this information, we can move this information into LTM
Information can be lost through decay (STM) and/or by interference
What are some limitations to the Modal model?
Cases such as HM suggest that information might not need to move through STM to get to LTM
What is the current consensus for the STM and LTM stores?
Both supported by the same neural networks but these may work in different ways of are involved to a different extent
What does Baddeley and Hitch’s model of working memory suggest?
We bring information into our short term or working memory and perform mental manipulations on it
- suggest visual and auditory memories are stored separately
3 main components:
- central executive
- Phonological loop
- visuospatial sketchpad
What is the central executive (WM model)?
Role in decision making, planning of responses, and coordinating the two other systems
What is the phonological loop (WM model)?
Deals with auditory, verbal info stored in an acoustic code
Has:
Articulatory loop (inner voice) - subvocal rehearsal
Phonological store (inner ear) - processes speech perception and stores spoken words
What is the visuospatial sketchpad (WM model)?
Stores visuospatial code, visual imagery etc
What supports Baddeley and Hitch’s model of working memory?
We can perform visual and audio tasks simultaneously
As well as neuroimaging
What is anterograde amnesia?
An inability to acquire new long term memories
What is retrograde amnesia?
A loss of memories acquired prior to amnesia
What kind of amnesia did HM have?
Medial temporal lobe amnesic syndrome
Severe anterograde amnesia
- Particularly for episodic
- Some new semantic info but no memory of learning this info
Retrograde amnesia for approx. 2 years prior to surgery and some selctive loss of certain events up to 10 years prior
What memory type was retained in HM?
Spared STM
Spared non-declarative memory
Digit span +1 test?
Researchers would read a list of digits and each time recited, would add another digit. Each time the patient would repeat these digits back
- Control participants do well on this can keep remembering
- patients with medial temporal lobe amnesia (HM), after the limits of STM (7+/-2 items) this task becomes difficult - this is the point where controls would rely on their long term memory
This is similar to the block-tapping memory span task in which HM performed very similarly once STM capacity ran out
How did researchers determine that HM still had some degree of semantic memory capabilities after the surgery despite anterograde amnesia?
Knew names and faces of celebrities who became famous after the surgery
Able to draw a floor plan of a home he lives in after surgery
HOWEVER
Couldn’t determine the source of this information (source amnesia)
Explain the case KC
Severe anterograde amnesia and retrograde amnesia
Some factual knowledge of life and intact for general world knowledge (semantic memory)
ALSO SHOWED INTACT CONCEPTUAL PRIMING (ability to learn new semantic memories)
What do cases like HM and KC tell us about episodic and semantic memory?
That they are supported by dissociable systems in the brain and semantic memory relies less on the hippocampus than episodic
EP case study?
73 year old man, developed severe amnesia following herpes - damage to medial temporal lobe
Could not acquire new episodic memories but could learn to make category judgements based on whether or not they belong to a previously viewed category
Preserved abilities to recognise previous events on the basis of signal strength or familiarity rather than recollection
HM showed normal implicit learning and non-declarative knowledge - how can this be tested?
Can be tested using procedural learning tasks such as:
- mirror tracing tasks
- serial reaction time task
What is a mirror tracing task? How did HM go on it?
Look in mirror and trace around an object eg. star
This task is difficult because you’re looking in a mirror and hand seems to go left but really goes right and vice versa
HM able to perform this task and be able to improve even though he had no recollection of learning it
Classical conditioning for HM?
Was able to learn a conditioned response in an eye blink task - puff of air and tone = eye blink response
When the gap between the two stimuli widens, becomes harder
What concepts of amnesia provide evidence for LTM consolidation?
Because we typically see a gradient of retrograde amnesia - older memories are more likely to be spared with newer ones more likely to be lost
Suggesting older memories are stored in a more permanent form
What is memory consolidation? and what processes are involved, what do they suggest?
How LTM develops overtime after initial acquisition
- Initial rapid consolidation involving the hippocampus and medial temporal lobe
- Slower permanent consolidation which is an interaction between the medial temporal lobe and neocortex
Suggests different structures are involved in acquisition and in storage
What does the dual trace theory suggest?
That the hippocampus holds memory until is is stored else where
What is the current view of the hippocampus’ role in memory consolidation?
That the hippocampus stores memory every time it is recalled - every time memory is recalled it becomes more resistant to disruption
What is the delayed non-match to sample task
Monkey moves sample object to obtain food and a screen is lowered, after a variable periods of time, monkey is shown the same sample object and another unfamiliar object - they need to remember to pick the new object and not the initial one
Lowered with medial temporal lobe problems - issues with object recognition
What is global cerebral ischemia?
Interruption of blood supply to the entire brain
RB case study?
Global cerebral ischemia - lost bloody supply during surgery
Had dense anterograde and retrograde amnesia (1-2 years)
Hippocampus appeared to be intact except for lesions in the CA1 cell layer
Are there any short term amnesic syndromes?
Yes - transient global amnesia
typically lasts 4-6 hours
occurs due to disrupted blood flow to MTL and diencephalon
sudden anterograde amnesia and variable retrograde amnesia 24-48hrs
What is korsakoff’s syndrome?
Caused by chronic consumption of alcohol
Results from thiamine deficiency (vit b)
Severe anterograde and retrograde amnesia - greater declarative loss
Which areas degenerate in Alzheimer’s?
The basal forebrain
- also diffuse to MTL and hippocampus
What is post traumatic amnesia?
Following a closed head injury - blow to head has resulted in concussion or coma
- Generally both anterograde and retrograde amnesia
What evidence (cell-based) has shown that hippocampus is involved in spatial memory?
Hippocampal place cells
Neurons that respond only when a subject is in a specific location
When a rat is first placed in an unfamiliar environment none of its hippocampal neurons have a place in that environment. As the rat familiarises itself with the environment, hippocampal neurons acquire a place field in it
obtain spatial info from GRID CELLS
What are entorhinal grid cells?
Entorhinal neurons that each have an extensive array of evenly spread place cells which map the corresponding environment
- head direction cells (when head turns in particular direction)
- border cells (fire when animal is at the border of a particular environment)
Time cells in MTL?
code time based aspects of an experience
Social spaces in MTL?
Learning about social organisation
Concept cells (Jennifer aniston neurons)?
Respond to ideas or concept of person or thing rather than visual stimuli etc.
Engram cells?
Encode for specific memories
- can use optogenetics to retrieve or forget these memories by exciting or depressing the neurons
In retrieval studies, what has been found regarding retrieval activation?
Left and right hippocampus were active only for the activation of correctly remembered words - not if they correctly thought they were familiar, not for misses etc
Not recognition based on familiarity alone
What brain area has increased activation during recognition confidence?
The perirhinal cortex
relates to familiarity based item retrieval
What is the BIC model of episodic memory?
Binding of items and context
What and who information as well as where and when information
Hippocampus is thought to bind this together to provide relational or episodic memory
What is LTP (long term potentiation)?
a process by which synaptic connections between neurons become stronger with frequent activation.
Develops only if the firing of the pre-synaptic neuron is followed by the firing of a post synaptic neuron the cooccurrence of firing in pre-and post synaptic cells is the critical factor in LTP
What is associative LTP?
Requires NMDA stimulation and Ca entry into the post synaptic neuron
Non-associative LTP?
Nothing occurring post-synaptically, facilitation is presynaptic and doesn’t require NMDA receptor stimulation
Explain NMDA and associative long term potentiation
NMDA receptors are blocked by mg ions, however, when glutamate binds to the AMPA receptors it depolarises the cell. This causes voltage dependent mg blockage to be removed allowing calcium ions to enter the cell via the NMDA receptor. This initiated cellular mechanisms that cause more AMPA receptors to be inserted into the cell membrane - the post synaptic cell is more sensitive to glutamate because it has more receptors to respond. STRONGER SYNAPSES
