Week 1 - introduction Flashcards
Learning definition
acquisition of an altered behavioural response due to an environmental stimulus
What type of learning applies to most learning?
associative learning
Memory definition
The processes through which learned information is stored. Memory can be short lasting or long lasting
Retrieval definition
A conscious or unconscious process that accesses stored information
What are three types of the experimental analysis of memory with examples?
Observations - e.g brain imaging
Loss of function - establishes whether a process is necessary for memory - e.g lesion studies
Gain of function - establishes whether a process is sufficient for memory - e.g Pharmacological activation of a molecule
Describe Karl Lashleys 1950 lesion study
Method:
Trained rats on a navigation task
Lesioned every part of the cortex bit by bit, in different orders
Results:
Huge variability in memory ability following rats cortical lesion
There is not one single brain region where all memories are located
His equipotentiality hypothesis proposed that other brain areas can compensate when one is damaged.
Conclusion:
Memory is distributed throughout
What is one criticism of Lashleys conclusion
He was considering general memory.
However we now know that specific memories are located in specific areas of the brain
He only lesioned the cortex, however modern day lesion studies show the the hippocampus, which is situated deeper in the brain is heavily implicated in memory
The task he used (maze learning) relied on multiple memory systems:
The maze task likely engaged procedural learning (motor skills and habits), which depends more on the striatum and cerebellum than on the hippocampus. So even if cortical areas were damaged, rats could still use other systems to solve the task.
His lesioning method was crude:
Using a soldering iron lacked the precision to isolate functional areas. This made it hard to target or interpret specific brain region involvement.
The engram is distributed, but not equally:
Lashley concluded that memory is widely distributed, which is partly true. However, we now know that different types of memory (e.g. episodic, emotional, procedural) are localized to different areas, and his tools weren’t sensitive enough to detect this specialisation.
Strengths and weaknesses of lesion studies
Strengths: Requirement of brain regions for memory can be determined. This will identify the location of stored memory
Show causal links between brain regions and memory.
Key historical findings (e.g. HM’s hippocampal lesion → loss of episodic memory).
In animals, allow controlled testing of memory functions.
Weaknesses: :
Lesion may affect performance in the behavioural task, preventing
assessment of memory. Lesion may also cause effects in other brain regions.
Early methods lacked precision, possibly affecting surrounding tissue.
Brain plasticity may mask memory deficits.
Lesions often disrupt multiple functions, not just memory.
Human lesion studies rely on natural damage, which is unpredictable.
Cannot show how memory regions interact in networks.
What are strengths and weaknesses of imaging studies
Flashcard:
Q: What are the strengths and weaknesses of imaging studies for understanding memory?
A:
Strengths:
Show active brain regions during memory tasks (e.g. fMRI, PET).
Non-invasive and safe for repeated use in humans.
Allow study of healthy individuals as well as patients.
Reveal network-level activity and functional connectivity.
High spatial resolution (especially fMRI) helps pinpoint memory-related areas like the hippocampus or prefrontal cortex.
Weaknesses:
Provide correlational, not causal, data—can’t prove necessity of regions.
Low temporal resolution (especially fMRI), missing fast neural events.
Complex tasks can activate multiple overlapping areas.
Can be affected by movement artifacts or individual anatomical differences.
Expensive and requires specialised equipment.
Describe the Morris water maze
The Morris Water Maze is a behavioural task used in rodents to study spatial learning and memory. Animals must learn to find a hidden platform submerged in a pool of opaque water using spatial cues around the room.
What is Semons 1921 proposal
Memories are stored as engrams
Engrams are lasting physical changes in brain state and structure that occur in response to an experience
strengths of animal experiments to study memory
Allow precise control over genetics, environment, and experimental conditions.
Enable invasive techniques (e.g. lesions, optogenetics, electrophysiology) not possible in humans.
Support causal inference about brain–memory relationships.
Shorter lifespans allow study of development and ageing.
Can use well-validated tasks like the Morris Water Maze to study specific memory types.
weaknesses of animal experiments to study memory
Species differences may limit how well findings generalise to humans.
Animals can’t report subjective experiences, limiting study of declarative memory.
Some memory types (e.g. autobiographical or semantic) are hard to model in animals.
Ethical concerns over invasive procedures and animal welfare.
Behaviour may be influenced by stress or motivation, not just memory.
First evidence of LTP, that would support the concept that hebbian plasticity exists
Bliss and Lømo (1973) discovered Long-Term Potentiation (LTP) in the hippocampus of anaesthetised rabbits. By delivering high-frequency stimulation to the perforant path (input to the hippocampus), they observed a long-lasting increase in synaptic strength at the dentate gyrus. This was the first evidence that synaptic connections could be strengthened through activity, suggesting a neural mechanism for learning and memory.
This supports the idea that Hebbian Plasticity exists HOWEVER, it does not prove that memory is dependent on hebbian plasticity
What is the hebb postulate?
neurons that fire together wire together
Describe the Autophosphorylation proposal of CaMK11q
Lisman (2017) proposed that kinase that can phosphorylate itself and could store memory. CaMK11 was discovered a year later that has Autophosphorylation properties and can possibly act as a memory storing molecule.
The CaMKII autophosphorylation hypothesis suggests that CaMKII (calcium/calmodulin-dependent protein kinase II) plays a key role in memory by sustaining synaptic strengthening after LTP induction. When activated by calcium influx during synaptic activity, CaMKII autophosphorylates, remaining active even after calcium levels fall—potentially maintaining LTP.
Evidence:
Genetic knockout mice lacking CaMKII autophosphorylation show impaired LTP and deficits in spatial memory (e.g. in the Morris Water Maze).
CaMKII accumulates at postsynaptic sites during LTP.
Blocking autophosphorylation disrupts synaptic plasticity without affecting baseline transmission.
Why do we need to understand learning and memory?
Discovery – Understanding the brain is one of the final frontiers for
human discovery and the capacity for learning vast amounts of
information and remembering over long periods of time are defining
feature of our brains. Gaining a deeper understanding of these
processes will help us address known needs in society, but also lead
to progress in many unexpected directions.
* Health – The average age of our population is increasing, and
memory deteriorates with age. Moreover, age is the primary risk
factor for various forms of dementia, including Alzheimer’s Disease,
Vascular Dementia, Lewy Body Dementias and Fronto-temporal
Dementia. Other learning deficits occur much earlier in life.
* Technology – Much of technology is inspired and influenced by our
own capacity for learning and memory, particularly in relation to
computers. Our capacity to recognize faces from varied viewpoints,
for instance, cannot be surpassed by computers. Much work is
required to understand how our brain solves that and many other
problems relating to memory.
* Education – By understanding more about the biological basis of
how humans learn we may dramatically improve our ability to
educate, either through developing new methods or
technological/pharmaceutical aids.
what is hebbian plasticity
Hebbian plasticity is the idea that synaptic connections are strengthened when both the presynaptic and postsynaptic neurons are active together—summarised by the phrase “cells that fire together, wire together.” It explains how experience can shape neural circuits and underlies learning and memory through mechanisms like Long-Term Potentiation (LTP).
Describe details of hebbian plasticity
Neurons wire together when one is repeatedly and persistently exciting the other
Its not the whole neuron that becomes more excitable when it is wired together with another neuron - it is the specific single connection between that neuron and another neuron
This often involves the LTD of other inputs. So you are essentially biasing the recipients neuron to one input over another
What is the cell assembly?
Donald Hebb proposed the cell assembly theory in 1949, suggesting that groups of neurons that are repeatedly activated together form a functional network or “assembly.” Once formed, activating part of the assembly can reactivate the whole, allowing for the storage and retrieval of memories. This idea laid the groundwork for understanding associative learning and the neural basis of thought and memory.
Cell assemblies are Groups of neurons that are connected through hebbian plasticity to mediate perceptual binding
Our memory system has the ability to complete a pattern based on limited information. Cell assemblies can explain this.
Assemblies (groups of neurons) are activated by a stimulus.
After the stimulus, activity reverberates across the neurons.
Hebbian plasticity selectively strengthens recipricol connections between particular active neurons.
The strengthened connection among the neurons contain the engram.
Partial stimulus activates part of the assembly/the engram, which in turn activates the whole assembly (pattern completion)
What is the phase sequence?
A phase sequence is a series of cell assemblies that activate in a specific order, proposed by Donald Hebb to explain how complex thoughts and behaviours unfold over time. When one cell assembly is activated, it can trigger the next in the sequence, forming a chain of neural activity that represents structured mental processes, such as thinking, planning, or recalling events.
Outline Clayton, Bussey and Dickinson’s scrub Jay studies
Scrub jays have sophisticated episodic memory
They hide their worms and nuts and remember exactly where they buried them
They always recover the worms before the nuts because nuts are preserved for longer
If another bird is watching them bury the food, they will come back later when they are no longer watching, and move all their food
Outline Kandel’s study on habituation in aplasia sea slugs
aplasia have giant neurons that are easy to clamp and get intraneuron recordings
He discovered habituation
If you squirt water onto the slugs gill it will initially withdraw the gill. If you keep doing it it will stop the gill from withdrawing.
Kandel found that as this happens, the sensory neuron is as electrically active as before, however the motor neuron is no longer active. This suggests that the synapse has weakened.
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Why is most memory work on mice?
It is mammal - more related to humans
It produces large litters
Short gestation time
Matures quickly
Amenable to genetic engineering: molecular mechanisms can be suppressed or enhanced; cell type markers and activity-dependent markers can be expressed; opto-genetic and chemo-genetic actuators can be expressed; diseases with known genetic causes can be modelled
