L09 - Memory Flashcards
What is the history of memory?
When we try to understand something, we often look back and look at our history (i.e.) is there a god for this?
Spiritual explanations
Egypt – Thoth – god of learning memory, wisdom, scribe of the gods.
Greece – Mnemosyne – Goddess of memory. Mother of the muses.
Greece – River Lethe
The river of forgetfulness
Runs through Hades – where gods go when they die
Drink from a specific river to go to Hades
Rome – Minerva Goddess of learning, memory and wisdom
What is memory?
Everything that makes us human and defines you as a human being as well as how you see yourself is MEMORY
When it’s gone, you cease to exist
How is it possible that we keep experiences around; we can teach someone something and five days later they are able to do it
Retain a skill they could not do before
What is it in the nervous system that changes for this to happen? How does it change? Is it encoded in our DNA?
What do we think when we see “the brain as a computer?
The brain is nothing like a computer but this is what is more natural to us. For the Greek, it was Gods.
The brain as a computer would look like
Information-processing perspective: “Brain (and so memory) is like a digital computer.”
- Processes (how are memories created, maintained, revived?)
- Encoding, Storage, Retrieval, Recall
- Hardware
Representations – what is stored, retrieved, recalled
- A memory representation (memory trace, memory record) is a unit of information, that can be processed.
- Software
Structures – Where are memories stored, retrieved from/to, recalled from/ to?
- Short-term store: like RAM of computer – restricted capacity; holds information for a short time.
- Long-term store: like the hard disk of a computer – nearly infinite capacity; holds information almost forever
How would you describe the hardware if we are comparing the brain to a computer?
Info – Auditory, Visual, Tactile etc.
Code – Relatively faithful
Capacity – large but limited
Duration – most info decays within seconds and is permanently lost
How would you describe the short-term memory if we are comparing the brain to a computer?
Code – acoustic, linguistics
Capacity – small
Duration – indefinitely if rehearsed, decay within 18-30 seconds if not continuously rehearsed.
How would you describe the long-term memory if we are comparing the brain to a computer?
Code – semantic?
Capacity – unlimited?
Duration – indefinitely?
Who is Henry Molaison (HM)?
This was the beginning of our modern explanation on how the memory and brain are related and work together.
Point of origin of modern memory research
HM had severe epilepsy (about 10 seizures per day). This was dangerous so he had surgery to the hippocampus (origin of epilepsy)
What surgery did HM go through?
He had a bilateral hippocampectomy (removed both hippocampus) to treat his epilepsy
Led to grading retrograde and amnesia for episodic memories (hippocampus is the center for episodic memories)
What is the mirror tracing experiment?
HM would not remember that he did this test the day before ever but he always got better
↳ We know where the brain is not working anymore → took out the hippocampus
↳ Implies: if you want explicit memories, you need a hippocampus
This case is so important because we had completely perfect characterization of what he could and could not do without the hippocampus
What was impaired after HM’s bilateral hippocampectomy?
Episodic memories – formed “on the fly” (made automatically) (Ex. What you ate for breakfast)
Recognition memory for recent objects and places
Explicit memory tasks
*Ex. Seven seconds reset man
What was preserved after HM’s bilateral hippocampectomy?
Semantic memory (do not lose knowledge about the world)
Priming
Procedural memories (mirror tracing experiment, riding a bike…)
Conditioning (dog, bell, treats (works with human that do not have a hippocampus))
Implicit memory tasks
What is declarative memory?
Hinges on hippocampus
Allows us to consciously recollect events and facts
Episodic memory
Semantic memory
What is non-declarative memory?
accessed without consciousness or implicitly through performance rather than recollection
Does not hinge on the hippocampus
Accessed without consciousness or implicitly through performance rather than recollection
Procedural memory
Priming
Classical conditioning
Non-associative learning
What is plasticity?
A change in neural morphology as a response to environmental stimuli
The brain is not hardwired, but able to respond to adaptive pressure by changing its structure and fundamental organisation
What is synaptic plasticity?
Refers to the phenomenon that the morphology of connection between neurons can change as a function of experience. This form of plasticity is thought to form the neurobiological basis of learning and memory formation
Memories are made by changing the structure of the synapses.
AMPAR channel – Sending signals to change the synapses to increase the number of connectors at the synapses.
What is cortical plasticity?
Refers to the phenomenon that cortical organisation can change in response to brain injury, such as strokes, lesions, etc…
This involves synaptic plasticity to some extent
Neuron controlling right are die but other areas in the brain that are functional take over that function (get “recruited” to control right arm)
What are the normal sensory perceptions of where something is coming from?
Occipital areas receive predominantly visual input
To a lesser extent also received tactile and auditory input
What are the sensory perceptions when there is visual deprivation involved?
When visual input is blocked for prolonged periods (ex. 2 weeks), the occipital lobe receives no more visual stimulation
This means that the auditory and tactile stimuli recruit more processing resources from the occipital regions than before
What is the law of regression?
Instable memories are more likely lost that stable ones.
What are the areas that process sensory stimuli?
Auditory, visual and tactile cortex – where memory is held
What is amnesia?
Memories that are lost are the most recent ones (typical cases)
Past memories stay intact when you have amnesia, you do not lose many.
Very strong amnesia however when you are trying to make new memories
Cannot recover them
New memories are not stable
What is the Perseveration-Consolidation hypothesis?
Repeating something to yourself multiple times will help you remember
If you are interrupted, you are most likely to forget them.
What is the current consolidation “dogma”?
Memories are labile after acquisition and are fixed (i.e.) permanently stored (consolidated) over time.
Consolidated memories are stable and can persist long-term
Consolidation is a transient, unidirectional process that occurs only after acquisition
Disruption of consolidation impairs memory formation and therefore reduces what will be retained.
What is the Synaptic (or cellular) consolidation hypothesis?
What behavioural neuropsychologists use
They encode new memories
Learning leads to changes in the connections between neurons
These modifications are unstable at the beginning, shortly after learning.
In order for long-lasting memory to form, the synaptic modifications need to stabilize.
The process that stabilizes these changes is called synaptic consolidation
What is the System consolidation?
What cognitive psychologists use
Can explain HM phenomenon – need hippocampus for new memories (episodic memories)
Certain types of memories (e.g., memories of events) initially require the hippocampus.
Over time, these memories undergo a transformation in terms of which brain structures are mainly involved for their expression. This process is called systems consolidation.
During systems consolidation, the expression of these memories will involve the hippocampus less and less, but more and more frontal areas
What is the spine remodelling during learning?
Conditioning increases the amount of spines on a neuron (synapses) in the hippocampus
After training, you see a shift in spine density (more spines); more connections between neurons
Learning induces change to the synaptic connections between neurons
Synaptic consolidation probably works on these changes and probably stabilizes and optimizes over time
Post synaptic density – part of the dendrite spine (top part)
What is Long-term potentiation?
“LTP [is an] experimental [phenomenon], which can be used to demonstrate the repertoire of long- lasting modifications of which individual synapses are capable.”
Experimental approach
Neuron is capable of changing its synaptic connection in light of stimulation
Note: Long-term depression represents the opposite effect, a decrease in the likelihood that the post-synaptic neuron will fire given a certain stimulation intensity.
Hebbian Learning
Hebb’s STM-LTM model
Psychology is a biological science – finding how neurons and synapses from memories. Argues that neurons firing themselves as an ongoing activity makes memories
What Hebbian learning supports the short-term memory model?
The pattern can stay active on its own for a while after the experience.
Recurrent connections among neurons of the cell assembly keep the pattern activated in a short-term.
What Hebbian learning supports the long-term memory model?
After a while, recurrent activity leads to changes in the synapses of the cell assembly.
As a consequence, the pattern can be recreated at a later time as a long-term memory.
