wk5: ND - Plasticity and Learning

Question 1

What enables experience dependent plasticity?

Answer 1

Hebbian synaptic mechanisms

Question 2

What Hebbian synaptic mechanisms are there? (2)

Answer 2

Long term potentiation
Long term depression

Question 3

Explain long term potentiation

Answer 3

When an axon of cell A … excites cell B and repeatedly or persistently takes part in firing it some growth process or metabolic change takes place in one or both cells so that A’s efficiency as one of the cells firing B is increased”.

Question 4

What type of synapse will undergo long term potentiation?

Answer 4

Synapse with vigorous pre- and post-synaptic activities

Question 5

What type of synapse will undergo longterm depression?

Answer 5

synapse with poor or no presynaptic activity

Question 6

Describe 3 theories about the termination of the critical period

Answer 6

1. When axonal growth stops
2. When synaptic transmission fully matures
3. When activity of neuromodulators in certain cortical areas decline

Question 7

What are the 2 classical dogmas that define plasticity beyond the critical period. What is the consequence of these dogmas?

Answer 7

1. Nerve cells in the adult do not divide
2. There is no significant growth of nerve fibres

Consequence: only changes in synaptic strength (i.e. Hebb synapse) can mediate plasticity

Note: the dogmas are wrong however

Question 8

What evidence is there that counters currently established classicial dogmas for plasticity after the critical period?

Answer 8

Neural stem cells have been shown to divide, differentiate and even find the right targets and behave within physiological ranges
Axons and dendrites can sprout too

so the dogmas are wrong

Question 9

What does admin of the antidepressant fluoxetine lead to in adult rats?

Answer 9

enables induction of ocular dominance shift by monocular deprivation

Question 10

What is the role of the critical period during early development? (2)

Answer 10

Help fine tune and calibrate cortical cells
Adapt developing neurons to new environment

Question 11

In a study by Lamberto Maffei and colleagues in Pisa, what did they find in amblyopic rats treated chronically with fluoxetine?

Answer 11

recovery in both visual acuity and C/I (contralateral/intralateral) VEP ratio. This suggests restoration of plasticity beyond critical period

Question 12

What neat trick can you do o give yourself a bigger orgasm?

Answer 12

“Slice off your leg” - Trichur Vidyasagar

Question 13

How can we describe sensory innervation of different parts of the body? How does this model relate to the phantom limb concept

Answer 13

Sensory homunculus. If a limb or part of body is removed, sensation may be felt if you signal an adjacent innervation area. E.g. you may feel phantom hand sensation when touching ipsilateral face

Question 14

How are different areas of innervation in the brain represented on the sensory homunculus?

Answer 14

Representations for different parts of the brain are different. e.g Face = large resolution and large representation

Question 15

What did pons et al. 1991 find about long term deafferentation? (1)

Answer 15

that it leads to extensive changes in cortical maps

Question 16

What did Vilayanur Ramachandran (Sagar’s classmate, who is on youtube) conclude about phantom limbs?

Answer 16

he concluded that when the hand area loses input when amputated, adjacent areas (on homonculus) take over.

Question 17

Can patients with a phantom hand feel sensation with a mirror image? Explain?

Answer 17

If you create a mirror image of one hand, and then stroke the real hand, patients with phantom hand will feel the stroking sensation of the missing hand seen in the mirror image. Lack of inputs means the somatosensory cortex is relying on visual information alone for sensory input in the phantom hand.

Question 18

Why do normal people with 2 hands not feel a sensation from stroking a hand with a mirror imaged hand in view?

Answer 18

Because they have more inputs beyond visual information, allowing the brain to veto the visual input

Question 19

According to research from Calford, Schmid and Rosa in 1999 on an eye lesion made in an adult cat and recorded 53 days later, what did they find happened to visual receptive fields?

Answer 19

Normal eye has normal receptive field
Lesion eye acquires receptive fields outside the lesion projection zone (adjacent to it)

Question 20

According to research from Calford, Schmid and Rosa in 1999: What percentage of single neurones in the lesion projection zones (LPZ) had “ectopic” visual discharge fields displaced to normal retina in the immediate?

Answer 20

75%

Question 21

According to research from Calford, Schmid and Rosa in 1999: How does the size of ectopic discharge fields vary from the size of normal discharge fields

Answer 21

They were pretty similar/not significantly different

Question 22

According to research from Calford, Schmid and Rosa in 1999: how did the responses to stimuli presented via ectopic discharge fields compare to presentations via normal discharge fields?

Answer 22

Were generally weaker

Question 23

Describe the 3 stages of the response to a partial loss of input to the topographically-arranged representations in sensory cortex

Answer 23

1. Immediate to hours: unmasking of new responsiveness
2. Hours to days: new filtering of the unmasked responsiveness; synaptic plasticity
3. Weeks to months: structural changes (local axonal sprouting, dendritic remodelling)

Question 24

Where is perceptual learning in most cases specific to? What idea does this lead to?

Answer 24

the retinal location of the stimulus, thus leading to the idea that it occurs early along the visual pathway, probably in area V1

Question 25

Is perceptual learning influenced by top-down processes? (e.g. attention)

Answer 25

yes