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NEUR 2000 > Lecture 16: Plasticity in Development > Flashcards

Lecture 16: Plasticity in Development Flashcards

1
Q

What is netrin?

A
  • A chemoattractant molecule that binds to the DCC receptor
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2
Q

Which guidance molecule is responsible for preventing developing axons from crossing midline more than once?

A
  • Slit
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3
Q

If one followed a growth cone through a ‘decision point’ at which a choice about direction must be made, the growth cone…

A
  • Extends filopodia and searches for environmental cues
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4
Q

What molecules support an innervating neuron, leading to its growth/survival?

A
  • Neurotrophic factors
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5
Q

In general, what is one role of neurotrophic factors?

A
  • Adjusting size of neuronal populations to an appropriate number
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6
Q

What type of mechanisms does neural development include?

A
  • Fairly stereotypical cellular and molecular mechanisms
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7
Q

Is neurodevelopment sufficient to account for behaviour/personality differences?

A
  • No

- Synapses can be reinforced/pruned based on activity patterns that can be heavily influenced by the environment

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8
Q

What is Hebb’s postulate?

A
  • Coordinated electrical activity of a presynaptic terminal and a postsynaptic neuron strengthens the synaptic connection b/n them
  • Neurons that fire together, wire together
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9
Q

What was Hebb’s postulate originally proposed to explain?

A
  • cellular learning/memory
  • LTP/LTD
  • But it is far more versatile
  • Long-term modifications in synaptic strength/distribution
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10
Q

What happens when inputs on a postsynaptic neuron are correlated?

A
  • Better able to activate postsynaptic cell

- Cause postsynaptic cell to acquire similar firing pattern

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11
Q

What happens when inputs on a postsynaptic neuron are poorly-correlated?

A
  • Gradually weaken
  • Are eliminated
  • Synapses lost and nerves may die off
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12
Q

What is the overall effect of Hebb’s postulate?

A
  • Creates synchrony within circuits of the brain
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13
Q

What are the 3 phenomena observed with the developing brain?

A
  • Behaviours not initially present emerge and are shaped by early experience (ex. learn to walk)
  • Superior capacity for learning complex skills and cognitive abilities early in life (extra sensitivity to environmental inputs)
  • Brain continues to grow after birth
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14
Q

What happens to neural circuits early in life?

A
  • Growth of dendrites and axons

- Combined with synaptogenesis

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15
Q

What happens to neural circuits later in life?

A
  • Pruning of weak or redundant synapses parallels strengthening of synapses that remain
  • Aim for energy efficiency
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16
Q

What does a neural circuit look like at birth, compared to 2 and 6 years?

A

Birth - not many connections, fairly spread out
2 years - very dense, lots of connections
6 years - more connections than birth, but less than 2 years due to pruning

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17
Q

What does the progression of synapses look like over time in the human brain?

A
  • Early rapid increase, then elimination of synapses

- Highest around 8 months

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18
Q

What does the elaboration of remaining synapses occur in synchrony with?

A
  • Sensory and motor abilities
  • Capacity for social interaction
  • Cognitive behaviours (ex. language)
  • Cellular connectivity reflects this
  • All sensitive to environment
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19
Q

What do mechanisms need to be combined with to explain development?

A
  • Flexibility demanded by dynamic environment
  • Typical experiences validate initial wiring
  • Diminished experiences can alter brain connectivity
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20
Q

Is the brain capacity for remodelling consistent?

A
  • No

- Eventual decline

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21
Q

What is a critical period?

A
  • Complex circuit formation during specific developmental time frames (temporal windows)
  • Some are quite constrained, others are less constrained
  • Although variable in duration/behaviours, all encompass time during which a behaviour requires specific environmental influences for normal development
22
Q

What did Konrad Lorenz find?

A
  • Goslings follow first large moving object they see and hear upon emergence from egg
  • Critical period lasts less than a day
23
Q

How can stimulus-evoked instincts be tested in a lab? What is the result?

A
  • Chicks on running wheel imprint on red circle

- Approach red circle and avoid blue square

24
Q

What is an example of critical period for ewes?

A
  • Ewes have 2-4hr after birth to imprint on scent of their own lamb
  • Otherwise will reject lamb
25
Q

What is a less constrained critical period?

A
  • Communication in songbirds and humans

- Extended period to ensure normal development

26
Q

What effect does environment have on neural circuitry?

A
  • Environmental influence elicits neural activity

- Nature of activity drives changes in synaptic connections

27
Q

What happens if there is a failure to be exposed to appropriate stimuli during critical period?

A
  • Difficult/impossible to remedy
  • Ex. visual development/language development
  • Deprivation of circuitry of chance to remodel during the critical period
28
Q

Where does visual system development occur?

A

Afferents of LGN of thalamus terminate in visual/striate cortex (occipital lobe)
- Layered (1-6)

29
Q

How do neurons respond to visual stimulation (except in layer 4)?

A
  • Neurons respond to varying degrees from stimulation in either eye
30
Q

What is different about Layer 4?

A
  • There are ocular dominance columns (alternating series of eye-specific domains)
  • All neurons are driven exclusively by one eye or ther other
31
Q

How can you measure which cells are innervated by a certain eye?

A
  • Injection of tracers into that eye

- Tracer is transported along visual pathway that corresponds to that eye

32
Q

Is ocular dominance seen in only layer 4?

A
  • No, seen in other layers

- Not as neatly organized

33
Q

How can you find categorization of ocular dominance?

A
  • Pass an electrode through visual cortex while responses of individual neurons to light stimulation in one or the other eye is recorded
34
Q

What are ocular dominance categories?

A
  • Defined based on frequency of AP activity elicited from visual cortical neurons following illumination in relevant eye
  • How often does that neuron fire?
35
Q

Describe group 1?

A
  • Driven only by contralateral eye stimulation
36
Q

Describe group 7?

A
  • Driven only by ipsilateral eye stimulation
37
Q

Describe group 4?

A
  • Driven equally well by both eyes
38
Q

What does the graph of ocular dominance groups look like in most layers?

A
  • Normal distribution with most cells in group 4 (being driven equally well by either eye)
39
Q

What happens when a cat has one eye closed b/n 1 wk and 2.5 months of age?

A
  • Cortical cells only responsive from ipsilateral, non-deprived eye
  • Recordings in retina and LGN layers indicate normal activity in response to electrical stimulation
  • Cortical blindness is permanent
  • Only group 7 neurons (or nt responsive)
40
Q

What is the result of monocular deprivation in an adult cat?

A
  • Outside critical period
  • Neuronal responses still driven by both eyes
  • Cortical activity is generally attenuated
41
Q

How many days of deprivation during critical period causes shift in favour of non-deprived eye?

A
  • 3 days
42
Q

What happens after 6 days of monocular deprivation during the critical period?

A
  • Causes a shift in favour of non-deprived eye nearly to extent of 2.5 months of deprivation
43
Q

What did Hebbian discover?

A
  • There is a competitive interaction for post-synaptic space b/n afferent axons driven by each of the 2 eyes during the critical period
44
Q

What is the result of competitive interaction that occurs from monocular deprivation?

A
  • Active eye gains competitive advantage

- Replaces many of the synaptic inputs that would have remained innervated from closed eye

45
Q

What happens to axons terminating in layer 4 from LGN after monocular deprivation during critical period?

A
  • Greatly reduced branching
46
Q

What is the result of binocular deprivation in the critical period?

A
  • Results in ocular dominance arrangement that, though attenuated, is similar in distribution to that of no deprivation (normal)
  • Indicates that balance of inputs shapes normal pattern of connections
  • Both eyes retain territory in cortex
47
Q

What does language development look like at 4 months?

A
  • Can distinguish all sounds measured by responsivity to novelty
48
Q

What does language development after 6 months look like?

A
  • Show preference for native language
49
Q

After about 12 months, what level of language development will the infant be at?

A
  • No longer respond robustly to phonetic elements particular to non-native language
50
Q

When does the critical period for new language fluency decline?

A
  • After age 7
51
Q

What does the cellular basis of language development in humans look like?

A
  • Evidence for shifted mode of processing
  • Neural regulation changes
  • Dominant brain structures used shifts

NEUR 2000 (10 decks)

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