Lecture 35: Cortical Circuits 2

Question 1

What does not significantly increase with age? What is the implication of this?

Answer 1

the number of neurons in the brain

learning and memories are generally not thought to be due to the formation of new neurons

Question 2

What is synaptic plasticity?

Answer 2

the change that occurs at synapses that enables them to alter the strength of communication between neurons

Question 3

What is Hebb’s rule?

Answer 3

neurons that fire together wire together

crucial to understanding the cellular basis of learning and memory

Question 4

What happens when axon A is near enough to excite cell B and repeatedly or persistently takes part in firing it?

Answer 4

some growth process or metabolic change takes place in one or both cells such that A’s efficiency, as one of the cells firing B, is increased

Question 5

What occurs during long-term potentiation?

Answer 5

synaptic connections become stronger (ie synaptic strength increases)

Question 6

What happens during long-term depression?

Answer 6

synaptic connections become weaker (ie synaptic strength decreases)

Question 7

What is the role of spike timing dependent plasticity?

Answer 7

adjusts the strength of connections between neurons according to the timing of the synaptic input

Question 8

What are some examples of spike timing dependent plasticity?

Answer 8

if A fires before B, then the response is potentiated resulting in LTP
if B fires before A, then the response is depressed resulting in LTD

Question 9

What time scale does spike timing dependent plasticity operate on?

Answer 9

on a millisecond time scale in vitro

e.g. if A fires less than 50ms before B, then LTP occurs and if B fires less than 50ms before A, then LTD occurs

Question 10

What time scale does synaptic potentiation during behaviour occur on?

Answer 10

longer time scales than previously recorded in the brain slice

Question 11

What can plasticity occur in response to?

Answer 11

synaptic input that arrives seconds before and after cell firing e.g. if cell A fires within 2 seconds of cell B

Question 12

Where has behavioural timescale synaptic plasticity been illustrated?

Answer 12

only in the hippocampus

Question 13

What are the forms of synaptic plasticity?

Answer 13

the strength of existing synaptic connections changes

dendritic spines may change morphologically by either growing or shrinking

Question 14

What does synaptic input from synaptically coupled neurons generate?

Answer 14

a synaptic potential (EPSP)

Question 15

What does the EPSP depend on?

Answer 15

many factors, including receptor selectivity and density

Question 16

What can the amplitude of the EPSP undergo?

Answer 16

LTP or LTD (because it is plastic)

Question 17

What occurs following pairing of pre-synaptic extracellular stimulation with a post-synaptic action potential?

Answer 17

the synaptic response (EPSP) in the postsynaptic neuron is increased from baseline (LTP)

Question 18

How can the morphology of post-synaptic spines change?

Answer 18

can change in size following certain patterns of synaptic input (because they are plastic)

Question 19

How can new connections (spines) be formed?

Answer 19

instantly

spines formed in response to the release of glutamate (via uncaging) near a dendritic branch

Question 20

How often does a new spine rapidly form following glutamate uncaging?

Answer 20

in ~10% attempts

Question 21

What can structural plasticity rapidly generate?

Answer 21

new connections in a dendritic location where there wasn’t a spine previously

Question 22

Why are there only a handful of direct examples of plasticity during learning in vivo?

Answer 22

this is due to the difficulty in recording from small structures (spines, axons) in vivo

Question 23

What has the advent of advanced experimental techniques enabled?

Answer 23

plasticity and learning to be measured in vivo -> namely two-photon microscopy and genetic fluorescence indicators

Question 24

How does two-photon microscopy work?

Answer 24

two-photon excitation arises from the simultaneous absorption of 2 photons by a fluorophore in a single event -> enables fluorescence imaging to be performed deep into tissue

Question 25

What alters the morphology of spines in the barrel (vibrissae) cortex?

Answer 25

altering synaptic input to spines (via sensory deprivation)

Question 26

When does the number of new spines formed daily increase?

Answer 26

during motor learning

Question 27

What does learning increase?

Answer 27

new connections between neurons

Question 28

When does the synaptic activity of cortical neurons change?

Answer 28

following learning of sensory-association

Question 29

How can plasticity of the synaptic response to sensory input be measured?

Answer 29

by measuring the change in calcium between pre-(naïve) to post-(expert) learning

Question 30

What is modulated following learning in vivo?

Answer 30

synaptic strength

Question 31

What is the hippocampus thought to drive?

Answer 31

long-term memory formation and retrieval

Question 32

What is the cortex known to be a major player in?

Answer 32

working memory, especially the prefrontal cortex

Question 33

What is working memory?

Answer 33

the temporary holding of information

enables us to dynamically change and manipulate stored information

Question 34

What are examples of working memory?

Answer 34

following instructions, responding in conversations, remembering phone numbers

Question 35

How can working memory be tested?

Answer 35

using a ’delay’ task where working memory must be used during a delay imposed between the stimulus and response

Question 36

What are the benefits of a behavioural ‘delay’ task?

Answer 36

the ALM has increased action potentials during the delay/working memory period