4 - HEBBIAN LEARNING

Question 1

what is hebbian learning mediated by?

Answer 1

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

Question 2

hebbian learning

what is long-term potentiation (LTP)?

Answer 2

• post synaptic cell responds more strongly to input (>PSPs = larger PSP)
• after a period of persistent strong (high frequency) input

Question 3

hebbian learning

what is long-term depression (LTD)?

Answer 3

• post synaptic cell responds less strongly to input (

Question 4

describe coordinated cell assemblies

Answer 4

• 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)

Question 5

how does learning make molecular changes in the brain in the short term?

(pre/post synaptic levels)

Answer 5

• 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

Question 6

how long do short term molecular changes take to make to the brain?

Answer 6

seconds-minutes

Question 7

how does learning cause long term structural changes to the brain?

(2 things)

Answer 7

• 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

Question 8

how long do long term structural changes take to make?

Answer 8

within minutes (30) to a few hours of constant activity

Question 9

graphs

Answer 9

see week 4 page 5

Question 10

why are septal nuclei, amygdala and hippocampus important for learning?

Answer 10

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

Question 11

evidence that the hippocampus is a ‘gateway’ for establishing new connections between cell assemblies

Answer 11

animal evidence - gene-manipulated mice with increased number of NMDA receptors show increased spatial abilities (can learn more complex mazes)

Question 12

could a memory pill that increases the number of NMDA receptors in the hippocampus improve learning in humans?

Answer 12

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

Question 13

what two processes determine electrochemical neural changes in the brain?

(2 things)

Answer 13

• short term molecular changes due to increased (coordinated activity)
• long term structural changes following molecular changes

Question 14

neural structures are determined by what two things?

Answer 14

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)