L24 - Plasticity & Learning (TV)

Question 1

Hebbian synaptic mechanism of LTP and LTD

Answer 1

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

Question 2

3 Theories about termination of critical periods - when do critical periods end?

Answer 2

When:

1) Axonal growth stops, they lose their ability to change terminal length
2) Synaptic transmission has fully matured from changes in post-synaptic receptors (e.g. density)
3) Activity of neuromodulators (NA, Ach) in certain cortical areas decline

Question 3

Plasticity beyond critical periods - classical dogmas vs emerging views

Answer 3

Classical dogmas:

• No division or growth in adult nerve cells
• Only changes in synaptic strength (Hebb synapse) can mediate plasticity

Emerging views

• Plasticity can be restored
• Neural stem cells can divide and differentiate
• Axons and dendrites can sprout

Question 4

Restoring plasticity beyond critical period - what can be administered to adult rats enable induction of ocular dominance shift by monocular deprivation?

Answer 4

Admin of antidepressant, fluoxetine

Question 5

Explanation of phantom limbs

Answer 5

Phantom limb is felt since there is massive cortical reorganisation e.g. nerves connecting to hands now reconnect to the face. This is why you might feel like your hand (which is amputated) is hurting when you touch your face (but might not always be face, could reconnect to other areas

Question 6

Place a mirror so that it shows the right hand in the mirror, where the mirror image is meant to be the left hand (amputated). Stroke the right hand and you will also see the mirror left hand being stroked and you can also feel it - could be due to visual system sending input to S1

Using this mirror method can cure phantom limb pain - where if patient feels like phantom hand is digging into their skin, when they look at the mirror and see their mirror hand open, they are relieved of the pain

Answer 6

Place a mirror so that it shows the right hand in the mirror, where the mirror image is meant to be the left hand (amputated). Stroke the right hand and you will also see the mirror left hand being stroked and you can also feel it - could be due to visual system sending input to S1

Using this mirror method can cure phantom limb pain - where if patient feels like phantom hand is digging into their skin, when they look at the mirror and see their mirror hand open, they are relieved of the pain

Question 7

~75% of single neurons in the Lesion Projection Zones (LPZ) had ectopic visual discharge fields displaced to normal retina in the immediate vicinity - orientation tuning and discharge field size was fine but they respond less and not as well to faster velocities

Answer 7

~75% of single neurons in the Lesion Projection Zones (LPZ) had ectopic visual discharge fields displaced to normal retina in the immediate vicinity - orientation tuning and discharge field size was fine but they respond less and not as well to faster velocities

Question 8

Stages of the response to a partial loss of input to the topographically-arranged representations in sensory cortex

Answer 8

1) Immediate to hours - unmasking of new responsiveness
2) Hours to days - filtering unmasked responsiveness and synaptic plasticity
3) Weeks to months - structural changes (local axonal sprouting and dendritic remodelling)

Question 9

Practice makes perfect - this is also true for perceptual learning e.g. discrimination of motion, gratings, texture

Answer 9

Practice makes perfect - this is also true for perceptual learning e.g. discrimination of motion, gratings, texture

Question 10

Perceptual learning is very specific to the area of the visual field you practice it in, specific to the retinal location of the stimulus and the stimuli (e.g. orientation) - suggesting it occurs early along the visual pathway, probably V1

Perceptual learning is influenced by top-down processes such as attention and spatial integration

Perceptual learning may be one of the reasons that the primary sensory cortices preserve some potential for plasticity

Answer 10

Perceptual learning is very specific to the area of the visual field you practice it in, specific to the retinal location of the stimulus and the stimuli (e.g. orientation) - suggesting it occurs early along the visual pathway, probably V1

Perceptual learning is influenced by top-down processes such as attention and spatial integration

Perceptual learning may be one of the reasons that the primary sensory cortices preserve some potential for plasticity