Introduction pt 1

Learning definition

Learning (memory formation/encoding) = acquisiton of an altered behavioural response due to an env stimulus

-> can take place in a single trial or require many trials

-> most learning is associative (e.g. pavlovian)

Memory definition

= the processes through which learned information is stored

-> can be short-lasting (working/short-term memory) or long-lasting (long-term memory)

Retrieval definiton

Retrieval = a conscious or unconscious process that accesses the stores info

Learning -> short or long term memory -> retrieva

(additional processes: forgetting or memory updating)

Why study memory

Impaired in various diseases (dementia, PTSD, intellectual disability) etc

understanding how memory is formed, stored, recalled + modified:

-       understand human nature

-       develop treatments of memory dysfunction in disease

Dementia symptoms (7)

-       inability to learn new things

-       memory loss

-       inability to communicate

-       repeating questions

-       trouble managing money

-       trouble with reasoning

-       wandering/ getting lost

Experimental analysis of memory: observations

1.    Observations: provide evidence for a hypothesis

a.    E.g. brain imaging shows whether a particular brain region gets activated with memory retrieval

b.   But observation does not establish whether the observed process is important

Experimental analysis of memory: loss-of-function

2.    Loss-of-function: establishes whether a process is necessary for memory

a.    E.g. lesions of brain region, pharma block of a molecule or gene inactivation

Experimental analysis of memory: gain-of-function

3.    Gain-of-function: establishes where a process is sufficient for memory

a.    E.g. pharma activation of a molecule or gene overexpression

Where is the location of memory – lesion studies (Karl Lashley, 1950)

• what the study found

• strength of the study (1)

• weakness of the study (2)

Lesion studies – removal of different areas of the brain (cortex)

-> can still recall with cortex removed

-> there is no single brain region where all memories are located

Specific memories (e.g. spatial) are located in subregions of brain

Strength – requirement of brain regions for memory can be determined, this will identify the location of stored memory

-       Weakness - lesion may affect performance in the behavioral task, preventing assessment of memory, lesion may also cause effects in other brain regions

Where is the location of memory – brain imaging in humans 2004

• what did they do/find

• strength (1)

• weakness (1)

MRI – remember map of Toronto

fMRI -> red showed increased blood flow

= increased brain activity

Strength: identification of brain regions relevant for memory without inference

Weakness: Studies just observe activity in various brain regions but are these regions really important?

Where is the location of memory – behavioural studies with animals

Morris water maze: milky water + non-visible platform

Lesioned mice showed impaired learning in latency to finding platform

(animal experiments are informative about memory mechanisms in humans)

Engrams in the brain (Richard Semon, 1921) - what are engrams

= a lasting physical changes in brain state and structure that occur in response to an experience

(memory = stored as an engram in the brain)

Is there a cellular basis of memory? (Donald Hebb, 1949) - speculative

1.    Axon of cell A excites cell B

2.    And repeatedly/persistently takes part in firing it

3.    Some growth processes or metabolic changes take place in one/both cells

4.    So A’s efficiency as one of the cells firing B is increased

= postulated mechanism for learning + memory

Discovery of LTP (Tim Bliss + Lomo)

• what did they do and what did this show

• strength

• weakness

• anaesthetised rabbits

• 15Hz stim for 10 secs

• = inc synaptic transmission efficiency + overall excitability of post-synaptic cell population

• therefore supported Hebbian plasticity exists

• but did not establish its necessity for memory

Is there a molecular basis of memory? (John Lisman, 2017)

 

Autophosphorylation of CaMKII:

Speculative until block of CaMKII autophosphorylation impaired LTP + memory

Understanding memory (summary of sorts, 5 points)

1.    Molecular mechanisms (affected by e.g. some inherited/genetic mutations)

2.    Communication between neurons

3.    Engrams (neuronal cell assemblies) (affected by e.g.  some dev disorders)

4.    Specific brain regions (affected by e.g. stroke)

a.    Stroke -> lose hippocampal area (spatial learning) -> ischemia

5.    Behavioral memory