Neurobiology of learning and memory Flashcards
What is learning and memory?
Learning:
* Acquisition of new knowledge or information
Memory:
* Retention of learned information
What are the 2 main types of memory?
Declarative: Can declare verbally
* Generic (reference library: facts, words)
* Explicit (memory with awareness; what you wore yesterday - requires conscious effort)
Nondeclarative: Cant declare verbally, retained smtg over time but cant declare it
* Implicit (memory without awareness: past experience influences current task - procedural memory)
What brain regions are involved in the 2 types of memory?
Declarative
* Medial temporal lobe (hippocampus) Nondeclarative
- Procedural: cerebellum (muscular response), striatum (habits, skills) & amygdala (emotional response)
What are the 3 types of non declarative memory?
Ø Procedural (learning a motor procedure in response to sensory input)
* Non-associative learning: change in behavioural response to a repeated stimulus (e.g. Habituation & Sensitisation)
* Associative learning: forming associations between events (e.g. classical conditioning & instrumental conditioning)
What is STM?
- May last seconds or hours
- Easily disrupted (distraction, head trauma)
- Apparent holding capacity is approx. 7 words*
Working M is not just holding smtg in your head but also performing an operation on it (ex subtraction)
What is LTM?
- Events/facts held for days, months or years after storage
- Not easily disrupted
Distraction doesnt make you forget a childhood M
How do we learn to associate one thing with another?
Need to engage with the target, not just be exposed to it
How does information go from STM to LTM?
Information in short term memory is lost if not consolidated
For a memory to be stored long-term, it does not necessarily have to be a short-term memory first: It may be stored due to an emotional response, conscious effort Spaced-practice (repeating over time) is better than massed practice
Learning & Memory require what 4 main changes in brain function?
Neuroplasticity
- Neurogenesis: New neurons from precursor cells
- Neurodegeneration: Death of neurons and rearrangement of synapses
- Changes in Dendritic: Branching:
* Increases in dendritic branches
* Pruning of dendritic branches
- Long Term Adaptations to Synapses:
* Long Term Potentiation = enhancement of synapse strength
* Long Term Depression = weakening the strength of a synapse
* Strength = ability to produce EPSP to promote action potentials
Can we grow new neurons?
Yes! We have stem cells
* Embryonic (pluripotential stem cells can turn into anything) - taken from fertilised eggs (blastocyst)
* Tissue specific: Neural stem cells (ie stem cells which will become neurons)
* Development of mature cell depends on exposure to growth factors
Where are neural stem cells?
Ependyma cells line the ventricles
Neural stem cells lie beneath this layer
Neural stem cells are in the subependyma of the ventricular system
What are neural stem cells?
- Neural stem cells manufacture constitutively proliferating (CP) progenitor cells
- CP cells migrate out of subependyma and form new neural cells when exposed to certain conditions (e.g., growth factors such as BDNF)
- Evidence has shown migration of these cells to
– Cortex
– Striatum
– Olfactory Tubercles of forebrain - Migration of these new neurons are helped by the ependymal cells.
- The development of new neurons is called Neurogenesis
– A lot of neurogenesis also occurs in the dentate gyrus of the hippocampus
What is the link between depression and neurogenesis?
- Depression associated with decreased neurogenesis in hippocampus (dentate gyrus)
- Use of antidepressants enhance neurogenesis in dentate gyrus
What is the link between exercise and neurogenesis?
- Neurons change in response to our experiences
- Exercise enhances learning through neurogenesis in hippocampus
- Regular physical exercise may protect against cognitive decline and dementia as we age
- Environmental enrichment also shows benefit for learning and memory
Not specific to exercise, exercise is one way to enrich the env
How can we alter the neurons that we have on top of creating new ones?
Neuron death and rearrangement of synapses
* Normal neurodevelopment depends on the death of some neurons
* Neurons grow to meet ‘target’ neurons
* If a growing neuron does not get the growth factors (and guidance) it needs from target cells they die off
* Neuron death helps to focus the output of remaining neurons - smaller number of postsynaptic cells = selectivity of neurotransmission
What does experience do to dendritic branching?
- Neurons change in response to our experiences - they physically grow more dendrites
Animals in enriched environments have greater dendritic branching. They also have improved learning skills.
When learn a new skill, the dendrites in that area become more dense bc they receive more info
Similar to synaptic elimination, our dendrites can be pruned back
* For dendrites use it or lose it
* Dendrites that are not used regularly will be pruned back
If A does not receive input, the A dendrite will recede
What does experience do to cortical reorganisation?
Our cortex changes in order to accommodate the motor activity that we need / use
* Cognitive Behavioural Therapy can also produce reorganisation of our “neural circuits”
Neural circuits reorganise in all the situations that we learn new things
How do experiences change our synapses?
- Our synapses change in response to our experiences
- Synaptic Plasticity = long term changes in how our synapses work
- Long Term Potentiation
- Long Term Depression
How do we study learning in the aplysia?
Aplysia have been used extensively to study the neuroplasticity associated with sensitisation and habituation by investigating their gill withdrawal reflex
Simple invertebrates
Few and large neurons - easy to study
Their neurons are very similar from one aplysia to the next
What is the specificity of synaptic connections?
The more it’s used, the stronger it gets
The sight of the rose causes an EPSP. With repeated exposure to seeing the rose the EPSP will become large enough to produce an action potential: the synapse is strengthened
What is synaptic cooperativity?
Neurons that fire together, wire together
If two sensory signals are repeatedly received within 50 ms of an action potential they become linked and strengthened. This means that one signal can have the same effect as two
* High frequency stimulation is not enough to cause LTP
* EPSP in one part of the neuron requires an action potential to occur at the same time in order to produce HUGE depolarisations
* This results in back propogation (i.e., more positive to the dendrites from the axon hillock of the firing neuron)
* Synapses that co-operate to produce this action potential are wired together and can induce firing later on independently
What is synaptic associativity?
Neurons that fire together, wire together
Weak inputs paired with a strong EPSP and action potential will become stronger with more pairings
If two sensory signals are repeatedly received within 50 ms of an action potential they become linked and strengthened. This means that a weak signal can end up being a lot stronger.
What was Hebb’s theory?
The neural representation of objects is the pattern of all cortical cells activated by the external stimulus
Some cortical cells are simultaneously active in response to this object
If the simultaneous activity of these cells occurs for long enough (or repeatedly), there will be a change (growth) in the neurons to consolidate this
“neurons that fire together, wire together”
This means that only a certain number of cells in this assembly would need to be activated in order to represent a rose (e.g.): different combinations instead of needing many different neurons
Successful pairing only occurs if both signals occur within 50 ms of an action potential - requires huge depolarisations
How do different neurons fire differently?
Neurons fire at different frequencies (Hz)
When neurons fire they release neurotransmitter into the synapse
Frequency means the number of synaptic excitations per second
Low frequency = 1-5 Hz
High frequency = 50-100 Hz
Differences in firing frequencies can greatly alter communication between synapses
