Lecture 33- Neuroplasticity I Flashcards
What are the types of memory?
-Explicit memory:
- episodic memory, memory of episodes in context (polymodal= visual, auditory etc.)
- semantic memory= memory of facts
-Implicit memory:
- procedural (skill, riding a bike etc., motor patterns)
- associate: classical conditioning, operant conditioning -nonassociative: habituation and sensitisation
- working memory
- short term memory
- long term memory
What is consolidation?
- from short term into long term memory
- happens in the hippocampus, old part of the cerebral cortex, have only 3 layers
What is amnesia?
- loss of memory
- anterograde: feature of Alzheimer’s, one retains past memory but cannot form new long term memories
- retrograde: loss of old memories, generally caused by brain damage (trauma), for example electroshock therapy
What is classical conditioning?
- can help us understand how the brain stores memories
- dog salivates upon smelling food, pavlov taught the dog to salivate to the sound of the bell (as it associated the bell with the food)
- long description: When a dog smells food this elicits a response of salivating. This pairing of stimulus-response occurs naturally, it has not been specifically taught to the dog. Now lets suppose that every time we give the dog food we ring a bell, a stimulus that does not naturally trigger salivation. Eventually, upon the bell being rung, the dog will salivate, even though there is no food present. The dog has been classically conditioned to elicit the response of salivating upon hearing the bell because the bell has been previously paired with the delivering of food.
What are associations and the ability to alter synaptic strength important for?
- the synaptic network is incredibly complex
- learning and memory occurs through the changes in synaptic strength, major functional changes can occur without structural change
- this is the basis of learning, the plasticity of the connections
- the brain is forever reorganising itself, synapses are made, re-made and altered at all times
- Associations – or binding – are the essence of memories
- The ability to alter synaptic strength is the basis of associations made by the brain
How does a synapse get stronger?
- three main variables are Pr, probability of release; N= number of synapses; q= quantal size
- remember that in the CNS usually just one active zone per synapse (mossy fibre is special)
- N, can have number of synapses that are inactive (silent) as the right receptors not in the membrane (AMPA)
- both pre and postsynaptic the changes that can influence this
• Increase in Pr – Vesicles are more easily released (biochemical change) – More Ca2+ flux into the presynaptic terminal – More docked vesicles
• Increase in N – Unsilencing of synapses (pre or postsynaptic)
• Increase in q – Increase AMPA receptors – Change in AMPA receptor kinetics
What are the two types of LTP?
- associative is the most common (need NMDA receptor)
- non associative, mossy fibre has this, not as common (doesn’t need NMDA)
- the difference is the number of inputs
1. Non-associative: high frequency stimulation of a single synapse is sufficient to strengthen that synapse
2. Associative: requires simultaneous firing of multiple synapses
What is associativity?
• Base on the observation that LTP occurred only when the post-synaptic cell was firing simultaneously with the presynaptic cell.
-LTP when fire together
- Rationale: The post-synaptic cell has to be strongly depolarised for an input to facilitate LTP.
- Associativity thus requires many axonal inputs at once (but a minimum of two)
What is important for associative LTP?
- not simultaneous firing of A and B but almost, if lag of less then 0.5 msec than likely to have an LTP
- if asynchronous then won’t get LTP
- Associative LTP Potentiation occurs if A fires just before B
What happens if A fires after B?
- LTD occurs
- if A fires at a time that is useful then will have LTP
- if asynchronous then LTD
- LTD occurs if A fires just after B
What are the features of associative LTP?
1. Associativity/ Cooperativity
• For weak inputs to be potentiated they must be paired with strong inputs.
-if weak at the same time as strong then will get LTP, so can be strengthen via strong synapse
2. Specificity
• Strong repetitive stimulation of one pathway can be sufficient to elicit LTP in one pathway but not in other unstimulated pathways.
What is important about NMDA?
- ionotropic glutamate receptor
- glutamate will only activate NMDA only when depolarised membrane
- need depolarisation and glutamate
- There are similarities between conditions required for associative LTP and conditions required for NMDA receptor activation. Both require glutamate to be released at an already depolarised dendrite. Further, LTP requires calcium, and NMDA receptors provide a source of intracellular calcium.
