Lecture 10 - learning

Question 1

Example of sequence learning

Answer 1

• Asked to follow sequence
• If sequence random harder to learning = RT longer
• If sequence predictable can learn motor associations and sequencing needed to produced response = faster RT
• Gives important info about learning and memory:
• -> Interaction between implicit (procedural) and explicit (declarative) process
• -> Role of sleep
• -> Interference
• -> Consolidation
• -> Probabilistic learning

Question 2

Motor consolidation

Answer 2

• Memories consolidate in around 4-6 hours
• Offline learning:
• -> Skills improve between practice sessions
• -> Performance of task improved after sleep
• New memories = fragile
• Old memories = robust
• If learn skill and then learn interfering task –> motor memories of first task disrupted

Question 3

Primary somatosensory cortex (S1)

Answer 3

• M1 and S1 sit either side of central sulcus
• Send and receive signals from contralateral side of body
• If born with missing limb initial map already reformed and if injury remapping occurs and that area of cortex responding to touch will re-map into neighbouring area which is no longer being activated
• Phantom limb pain with injury group = brain receives signals from limb not there, depending on how mapping occurs can produce pain

Question 4

Non-associative learning

Answer 4

• Relatively permanent change in strength of respond to single stimulus due to repeated exposure to stimulus
• Habituation = reduction in response
• Sensitisation = increase in response
• Both short term and reversible
• Perceptual learning = increasing sensory discrimination with experience

Question 5

Associative learning

Answer 5

• Process by which association between 2 stimuli or a behaviour and a stimulus is learnt
• Classical conditioning = S-S association
• Motor learning in some forms e.g. cerebellum
• Instrumental/operant conditioning e.g. basal ganglia

Question 6

Relational learning

Answer 6

• Learning relationships between stimuli
• Spatial processing (maps)
• Declarative memory = constructing episodic memories

Question 7

Learning-based neural changes: synapse efficacy

Answer 7

Pre-synaptic:

• Increase vesicle volume
• Increase availability of vesicles
• Increase release probability

Synaptic cleft:

• Reduce re-uptake mechanisms
• Reduce gap dimensions

Post-synaptic:
-Increase receptor density/area

Growth – new synapse
-Make new synapses

Question 8

Spinal flexion reflex

Answer 8

• Withdrawal from cutaneous inputs (heat) rapidly habituates
• Complex pathway

Question 9

Aplysia (sea slug) gill withdrawal

Answer 9

• Simple nerve system
• Habituation to repeated tactile stimuli = functionally relevant to living in sea weed
• Sensitization preceding electric shock on the tail leads to enhanced gill withdrawal with light touch

Question 10

Habituation

Answer 10

Synaptic depression: down-regulation of synapse:

• Reduction in neurotransmitters released by synaptic terminals
• Fewer synapses
• Both lead to reduced strength of sensory neuron on motor neuron

Question 11

Sensitisation

Answer 11

• Synaptic facilitation: up regulation of synapse
• Increase in neurotransmitters released by synaptic terminals
• More synapses
• Both lead to increased strength of sensory neuron on motor neuron

Question 12

Hebbs rule

Answer 12

• Associative learning

- When neuron A repeatedly participates in firing neuron B, the strength of the action of A onto B increases

Question 13

Somatosensory remapping

Answer 13

• Rapid changes in somatosensory (or motor maps) evident after change in inputs
• Denervation = if remove input then neighbouring areas will encroach = through amputation of fingers, short term through nerve blockages, if cortex blocked

Question 14

Chances in map reflect…

Answer 14

• Long term changes in functional connectivity e.g. growth of neurons
• Branching (or pruning) of dendritic connections
• Neurons appear to compete for space in the cortex – unused cortex gets taken over by other inputs
• Imaging of the living mouse brain shows changes (growth and pruning) in dendritic branches in the mouse within hours or days of a new task

Question 15

Long-term synaptic plasticity

Answer 15

LTP:

• Activity-dependent persistent strengthening of synapses
• These produce a long-lasting increase in signal transmission between 2 neurons

LTD:

• Activity-dependent reduction in the efficacy of neuronal synapses
• Produce long-lasting decreases in signal transmission between 2 neurons

Question 16

Associative LTP induction

Answer 16

• Before learning have pre-synaptic state = vesicles of glutamate
• AP causes glutamate to diffuse across cleft
• Glutamate binds to AMPA and NMDA receptors
• AMPA = activated and produces response
• To increase strength of association want more AMPA receptors
• Processing in cell that allow AMPA to by synthesised and will placed on membrane = but need calcium
• Get calcium into cell = triggers cascade of responses
• Next time glutamate in cleft = get a stronger response
• NMDA doesn’t respond to glutamate = blocked by Mg ion
• When post synaptic cells sufficiently activated, electoral potential will expel Mg from NMDA
• Can fake this by stimulating cell with electricity
• When glutamate enters cleft = both AMPA and NMDA receptors open and allow usual sodium ions into cell
• NMDA also allows calcium into cell
• Calcium triggers process that manufactures more AMPA and plugs into membrane = more receptors

Question 17

Key principles of LTP

Answer 17

• Cooperatively = LTP requires simultaneous activation of large number of axons (due to large depolarisation)
• Associative: When weak synaptic input is paired with strong, then large depolarisation can propagate and cause LTP at synapse with weak input
• Synapse-specific: If particular synapse is not activated then LTP will not occur even with strong post synaptic depolarisation

Question 18

Importance of learning and memory

Answer 18

• Cooperatively: ensure that only event of a high degree of significant (that activate sufficient inputs) will result in memory storage
• Associative: allows even with little significant (CS) to be endowed with a higher degree of meaning, if associated with a significant event (US)
• Synapse specific: Inputs that convey info not related to a particular even will not be strengthened to participate in a given memory

Question 19

Long term depression

Answer 19

• First identified in hippocampus, thought to be major component of motor learning in cerebellum
• Cerebellar LTD involves decrease in AMPA receptors however not NDMA-dependent

Question 20

Measuring LTD in humans: TMS

Answer 20

• Sensors put on skin record muscle activity
• Electricity through coil that produces magnetic pulse = magnetic field applied
• Causes brief electric pulse –> twitch of muscle
• If done over motor cortex can activate betz cells = cause movement
• Measure time taken between pulse and response = distance signal travelled
• EMG records response = senses you place on skin that record muscle activity
• Can measure height of responses

Question 21

LTP and LTD like mechanisms in humans

Answer 21

• Can use TMS to measure LTD and LTP
• Can apply drugs that block receptors e.g. MDMA antagonist blocks LTP
• LTD not blocked by NMDA antagonist