4 - HEBBIAN LEARNING Flashcards
what is hebbian learning mediated by?
NMDA receptors
- specific neurotransmitter receptor protein
- required to open ion channel
- also, both pre and post synaptic cell must be simultaneously active
- presynaptic = release of glutamate
- postsynaptic = depolarised
- Mg++ (magnesium) ion sits in the channel - depolarisation kicks out Mg++ and the channel is now open
hebbian learning
what is long-term potentiation (LTP)?
- post synaptic cell responds more strongly to input (>PSPs = larger PSP)
- after a period of persistent strong (high frequency) input
hebbian learning
what is long-term depression (LTD)?
- post synaptic cell responds less strongly to input (
describe coordinated cell assemblies
- bilateral (two way) connections of the cortex via hubs (eg hippocampus, amygdala)
- both receive input simultaneously = strengthens connection between them
- when link becomes really strong, one can fire and cause the other to fire as well - associated to the other (associate two things together)
how does learning make molecular changes in the brain in the short term?
(pre/post synaptic levels)
- due to increased coordinated activity = increases pre and post synaptic areas
- presynaptic = more neurotransmitters released with every AP
- postsynaptic = more ion channels open or are added (more ions can enter with every AP = higher PSP)
- more can be added within seconds embedded into membrane
how long do short term molecular changes take to make to the brain?
seconds-minutes
how does learning cause long term structural changes to the brain?
(2 things)
- due to short term molecular changes
1- new synapses
2- shift in synaptic input
- axon collatoral = the new axon = rewired
- restructured as a result of organisms behaviour in the environment - children can change wiring through play
how long do long term structural changes take to make?
within minutes (30) to a few hours of constant activity
graphs
see week 4 page 5
why are septal nuclei, amygdala and hippocampus important for learning?
rich in NMDA receptors
- particularly suited to hebbian learning
- means fast association with stimuli or events with
- positive feelings=septal nuclei - selective seeking
- could impact mixed reared rats - know how to behave to elicit + response
- negative feelings=amygdala
- with each other=hippocampus - factual and relational learning - eg navigation and how places relate with each other
evidence that the hippocampus is a ‘gateway’ for establishing new connections between cell assemblies
animal evidence - gene-manipulated mice with increased number of NMDA receptors show increased spatial abilities (can learn more complex mazes)
could a memory pill that increases the number of NMDA receptors in the hippocampus improve learning in humans?
yes
- but hippocampus = extremely sensitive and unstable = susceptible to seizure activity (often cause of epileptic seizures) and anoxia (lack of oxygen)
- probable cause is great number of NMDA receptors and corresponding high metabolic demands = burden
- need to compromise
what two processes determine electrochemical neural changes in the brain?
(2 things)
- short term molecular changes due to increased (coordinated activity)
- long term structural changes following molecular changes
neural structures are determined by what two things?
1 genetics at a macroscopic level (visual) - adaptation through evolution
2 experience at the microscopic level (cellular) - adaptation through learning (rewiring and fine tuning based on environment)