Lecture 16: Plasticity in Development Flashcards
(51 cards)
What is netrin?
- A chemoattractant molecule that binds to the DCC receptor
Which guidance molecule is responsible for preventing developing axons from crossing midline more than once?
- Slit
If one followed a growth cone through a ‘decision point’ at which a choice about direction must be made, the growth cone…
- Extends filopodia and searches for environmental cues
What molecules support an innervating neuron, leading to its growth/survival?
- Neurotrophic factors
In general, what is one role of neurotrophic factors?
- Adjusting size of neuronal populations to an appropriate number
What type of mechanisms does neural development include?
- Fairly stereotypical cellular and molecular mechanisms
Is neurodevelopment sufficient to account for behaviour/personality differences?
- No
- Synapses can be reinforced/pruned based on activity patterns that can be heavily influenced by the environment
What is Hebb’s postulate?
- Coordinated electrical activity of a presynaptic terminal and a postsynaptic neuron strengthens the synaptic connection b/n them
- Neurons that fire together, wire together
What was Hebb’s postulate originally proposed to explain?
- cellular learning/memory
- LTP/LTD
- But it is far more versatile
- Long-term modifications in synaptic strength/distribution
What happens when inputs on a postsynaptic neuron are correlated?
- Better able to activate postsynaptic cell
- Cause postsynaptic cell to acquire similar firing pattern
What happens when inputs on a postsynaptic neuron are poorly-correlated?
- Gradually weaken
- Are eliminated
- Synapses lost and nerves may die off
What is the overall effect of Hebb’s postulate?
- Creates synchrony within circuits of the brain
What are the 3 phenomena observed with the developing brain?
- 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
What happens to neural circuits early in life?
- Growth of dendrites and axons
- Combined with synaptogenesis
What happens to neural circuits later in life?
- Pruning of weak or redundant synapses parallels strengthening of synapses that remain
- Aim for energy efficiency
What does a neural circuit look like at birth, compared to 2 and 6 years?
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
What does the progression of synapses look like over time in the human brain?
- Early rapid increase, then elimination of synapses
- Highest around 8 months
What does the elaboration of remaining synapses occur in synchrony with?
- Sensory and motor abilities
- Capacity for social interaction
- Cognitive behaviours (ex. language)
- Cellular connectivity reflects this
- All sensitive to environment
What do mechanisms need to be combined with to explain development?
- Flexibility demanded by dynamic environment
- Typical experiences validate initial wiring
- Diminished experiences can alter brain connectivity
Is the brain capacity for remodelling consistent?
- No
- Eventual decline
What is a critical period?
- 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
What did Konrad Lorenz find?
- Goslings follow first large moving object they see and hear upon emergence from egg
- Critical period lasts less than a day
How can stimulus-evoked instincts be tested in a lab? What is the result?
- Chicks on running wheel imprint on red circle
- Approach red circle and avoid blue square
What is an example of critical period for ewes?
- Ewes have 2-4hr after birth to imprint on scent of their own lamb
- Otherwise will reject lamb
