Plasticity and Learning

Question 1

What is postnatal growth of the brain guided by?

Answer 1

learning

Question 2

What is the critical period for visual cortex development in cats, monkeys, and humans?

Answer 2

• cat: 2 weeks - 3 months
• monkey: 2 months - 12 months
• human: 6 months - 3 years

Question 3

What is neuronal plasticity in the mammalian visual system driven by?

Answer 3

neuronal activity

Question 4

Eye closure for a couple days during ________________________ induces movement of __________________________________. This does not occur after ______________.

Answer 4

the critical period; spines as part of synaptic plasticity; the critical period

Question 5

What regulates the critical period?

Answer 5

cortical GABA inhibition

Question 6

TRUE or FALSE: inhibiting GABA signalling widens the critical period and increases plasticity

Answer 6

FALSE: enhancing GABA

Question 7

What eliminates the critical period?

Answer 7

GABA neuron knockout (GAD2)

Question 8

What are the 4 methods of critical period termination?

Answer 8

1. myelination, and associated Nogo, which occurs at the end of the critical period; Nogo inhibits neuronal growth
2. Development of adult perineuronal net (PNN), a web of CSPGs that wrap inhibitory neurons (GABA)
3. reduction in growth potential of adult neurons, compared to neonatal neurons
4. reductions in growth factors like BDNF and neuromodulators like NA (which modulate LTP)

Question 9

What is the function of PNN?

Answer 9

limit plasticity with maturation

Question 10

What are sone ways in which the PNN limit plasticity?

Answer 10

1. physical barrier
2. inhibitory molecules
3. prevent lateral mobility of receptors

Question 11

Missed skill development in critical periods leads to
____________________________.

Answer 11

smaller associated cortical areas

Question 12

What is the order of critical periods for the following: sensory, language, other cognitive and motor functions

Answer 12

1. sensory
2. language
3. other cog and motor function

Question 13

Children without social interaction in critical period have _____________________.

Answer 13

less related frontal cortex

Question 14

What are some ways via which critical-period plasticity may be restored in adults to treat SCI?

Answer 14

1. blocking myelin inhibition of axon growth (eliminate Nogo)
2. degrading PNN with chondroitinase (ChABC)
3. transplant immature GABA neurons in visual cortex
4. increase neuromodulators via antidepressants
5. training or enriched environment to increase BDNF (use it or lose it)
6. microglia-neuronal communication increases GABA neuron plasticity

Question 15

What does ChABC digest?

Answer 15

CSPG and PNN

Question 16

Transplanting inhibitory GABAergic neurons creates _______________________ in mice.

Answer 16

a new critical period

Question 17

What does enriched environment lead to, in terms of plasticity?

Answer 17

• increases cortical thickness
• increases size of neurons
• increases number of spines/synapses
• increaes BDNF

Question 18

Which reflex can be readily studied in humans to examine plasticity and learning? Why?

Answer 18

• monosynaptic stretch reflex
• resists external disturbances

Question 19

Why do we need to regulate the stretch reflex?

Answer 19

because it can get in the way of voluntary movement

Question 20

______________ inhibition turns off antagonist motor neurons when making movement. This is _____________ inhibition.

Answer 20

reciprocal; postsynaptic

Question 21

TRUE or FALSE: Nodal Facilitation (GABAB) turns off reflex pathways when not needed and Presynaptic inhibition (GABAA) turns on sensory transmission to the brain.

Answer 21

FALSE:
- presynaptic inhibition (GABAB) = turn OFF reflex when not needed
- nodal facilitation (GABAA) = turn ON sensory transmission to brain

Question 22

TRUE Or FALSE: GABAA modulates afferents to the brain, whereas GABAB increases synaptic inhibition

Answer 22

TRUE

Question 23

Where are GABAA and GABAB receptors found on an axon?

Answer 23

• GABAA at nodes
• GABAB at terminals

Question 24

Describe Nashner’s 1979 experiment. What was the main conclusion?

Answer 24

• ankle extensor stretch reflexes REDUCE body sway if foot is displaced horizontally, so the CNS AUGMENTS them in successive trials
• the same reflexes INCREASE body sway in a toe-up rotation about the ankle joint, so the CNS ATTENUATES them in successive trials
• main conclusion: context-dependence and adaptation may be controlled by cerebellum and reticular formation (i.e. good control can take over the reflex that makes you fall over)

Question 25

Delays in the stretch reflex can cause ___________________________.

Answer 25

instability and tremor

Question 26

TRUE or FALSE: experienced athletes and dancers have an enhanced stretch reflex

Answer 26

FALSE: they lack the stretch reflex

Question 27

Why do experienced dancers and athletes lack the stretch reflex?

Answer 27

it can get in the way of their movements; i.e. the body has adapted inhibition of the stretch reflex and tremor

Question 28

What happens to muscle oscillation if the stretch reflex is too late?

Answer 28

oscillations become bigger if the stretch reflex is activated at the wrong time, leading to tremor

Question 29

With spinal cord injury, nerve injury, stroke or CP, the reflex pathways are disrupted, leading to __________________.

Answer 29

spasticity

Question 30

With spinal cord injury, what does reduced reciprocal inhibition lead to?

Answer 30

co-contraction of muscles, leading to stiffness

Question 31

With spinal cord injury, what does reduced preynaptic inhibition (via GABAB) lead to?

Answer 31

exaggerated reflexes

Question 32

With spinal cord injury, what does sensory terminal sprouting and microglia plasticity lead to?

Answer 32

increased reflexes, which lead to spasticity and clonus

Question 33

With spinal cord injury, what does increased nodal facilitation lead to?

Answer 33

unwanted reflex response in inappropriate muscles

Question 34

What factors in spinal cord injury lead to spasticity or clonus?

Answer 34

- reduced reciprocal inhibition - reduced presynaptic inhibition - sensory terminal sprouting and microglia plasticity - increased nodal facilitation

Question 35

In motor neurons, what leads to sustained muscle spasms?

Answer 35

increase Na+ and Ca2+ currents

Question 36

_____________ innervation of the spinal cord is lost, but _____________ receptors on motorneurons become constitutively active, further augmenting spasms.

Answer 36

serotonin, 5HT

Question 37

What is used to treat spasticity?

Answer 37

- GABA agonists - 5-HT antagonists - botox - surgery - rehab

Question 38

What happens to brain mapping when the 3rd digit of your hand is removed? What is this change guided by?

Answer 38

- 2nd and 4th finger mapping takes over - guided by microglia

Question 39

Sensation in phantom limb is evoked from stimulation of the _________ after 4 weeks after arm amputation and cortical remapping in adults.

Answer 39

face