Lecture 6 - Chapter 24: Modification of Neuronal Circuits Flashcards
Describe what instinct is.
Instinct is hard-wired, preprogrammed behaviour. It’s automatic and can’t be suppressed. Once it is initiated, it has fixed-action patterns (FAPs). This means that once it is initiated, it has to continue.
What is imprinting?
Instinct and learning
What are critical periods in life?
Short periods in life in which environmental factors are especially influential in shaping connections and behaviour.
What is an example of instinctive behaviour with fixed-action patterns (FAPs)?
A goose that rolls back its eggs from outside the nest to the inside of the nest. The triggering stimulus is the rolling of the egg. When you take the egg away, the goose will continue to try to roll the egg back to the nest, even when it’s not there anymore. The behaviour cannot be suppressed by the goose.
What is another example of instinctive behaviour with fixed-action patterns (FAPs) in regard to sticklebacks?
Sticklebacks are fish and very social animals. The males tolerate each other, expect for when males start making nests. Males who make nests develop a red belly. The fixed-action pattern here is that a male with a red belly, will attack another red belly male.
Researchers saw that the color red in general makes sticklebacks more aggressive. Red is seen as a supernormal stimuli. They started to make fake fishes with different shapes of red colors and saw that all the sticklebacks became aggressive.
What is a supernormal stimuli?
It is an exaggerated version of a stimulus to which there is an existing response tendency, or any stimulus that elicits a response more strongly than the stimulus for which it evolved.
What are other examples of supernormal stimuli?
- Seagulls have a red dot on their beaks. When they have babies, the red dot is a signal for the babies to open their beak. You can get a red pencil as a supernormal stimuli and point this towards the baby seagulls, they will open their beaks to get food.
- This can also be done for eggs. Birds will always try to keep the biggest (healthiest) eggs in their nest. When you put bigger eggs in their nests, the mother will kick out her own eggs because they are smaller. The (fake) bigger eggs are the supernormal stimulus here.
What are supernormal stimuli in our daily life?
Advertisements are often based on supernormal stimuli.
- Colors red and yellow used for advertisment of junk food that is high in fat, sugar and salt (associations between colors and certain foods)
- Communication technology, in the past communication was essential for survival.
- Looking attractive for mating, being attracted to bigger lips
Depicted in the picture is classical conditioning of Pavlov’s dog, where for the dog ringing of the bell is associated with food. Is this a fixed action pattern?
No, because classical conditioning is not innate.
How does imprinting work (use geese as example)?
The first day after hatching is a critical period for the goslings for recognition and imprinting of the mother. After this critical period, the behaviour is irreversible. Movement is the trigger for this imprinting.
For what is imprinting important?
- Imprinting and instinct increase survival of the individual and hence of the species.
- Social contact
What happens in humans if imprinting fails?
E.g. social deprivation in first year increases the risk for psychological and social problems.
What’s Hebb’s postulate?
Coordinated activity of pre- and postsynapses strengthens their connections (use it or lose it).
It states that synchronized activity of the pre- and postsynaps, causes strengthening and survival of the synapse (use it). If there’s no synchronization, the synapse will lose the competition to synapses that do fire in synchronization and the synapse will ultimately weaken and dissappear (lose it).
What can be seen in this picture?
You can see that at birth, there are very few connections in the brain. At the age of 2 years, the amount of connections strongly increases. At 6 years, the amount of neurons stays roughly the same, however the amount of connections strongly decreases.
What is pruning?
Synaptic pruning is a natural proccess that occurs in the brain between early childhood and adulthood. During pruning, the brain eliminates extra synapses (use it or lose it). Also seen in the picture.
Does this mean that deaf children cannot develop language skills (because they cannot sense exogenous stimuli)?
No, deaf children indeed do not develop proper language. But they do learn to communicate via sign language during the same critical period.
What is seen in developing skill in a foreign language?
That the critical period for native acquisition of foreign language is around 12 years old.
Also, if you look at fMRIs you can see that children use different parts of their brain when they hear language
Describe how the visual system looks like in the brain.
Your eyes are connected to the visual cortex, where axons from both eyes first pass the relay station in the thalamus. Furthermore, an eye contains axons that receive information from the left and right side of one eye (also for the other eye). The axons that receive information from the left side of both eyes connect to the right side of the brain and vice versa.
An experiment was performed where radioactive peptides were injected into the retina of one eye. These peptides are then incorporated into proteins and anterogradely transported across the axon. What can be visualized in the brain?
With the incorporation of the radioactive label into one eye, you can see what parts of the brain (specifically thalamus and visual cortex) are activated by the specific eye where the radioactive labels were injected in. You can see this in the pictures, where the lighter stripes resemble the incorporated radioactive parts of the brain that are activated by the specific eye that received the radioactive inections. And the darker stripes resemble the neuronal tissue that is not activated by that eye (but are activated by the other eye without radioactive incorporation).
How are these stripes also called?
Ocular dominance columns
What is seen in a study performed on cats in regard to the cats’ visual system critical period?
They studied single electrode recordings during flashes of light to one or both eyes of the cat (contralateral/ipsilateral/both eyes). They saw that the cells that were activated by the flashes, had a normal distribution. Meaning that there were about the same amount of cells activated when light was shone on the one eye, as the other eye.
In another experiment, one eyelid of a cat was sutured close after birth (1 week to 2.5 months). What happened to the visual system of this cat when the eye was opened again (2,5 months till 38 months)?
At 38 months no response was seen from the eye that was sutured close for the short period of time. This was irreversible. It supports that the critical period of the visual system (of a cat) lies between 1 week and 2,5 months.
The last thing the researchers did was suturing one eye close for only 3 days during the critical period of a cat’s visual system (so somewhere between 1 week and 2,5 months). What did they see?
That also short periods of light deprivations strongly affect visual performance 2 months later.
How did researchers confirm that the critical period of a cats’ visual system lies between 1 week and 2,5 months?
By suturing 1 eye close in adult cats. When the eye was opened again, this had no effect on the number of activated cells.
What is the effect on brain morphology of light deprivation in one eye of a cat during the critical period of the visual system?
What you can see in the picture, is that the left picture displays ocular dominance columns that are present at birth. On the right, where light deprivation of 1 eye was performed, you see wider ocular dominance columns of the other eye (use it or lose it).
Just study this picture as it supports what is discussed before. You can see the effect of light deprivation on neuronal morphology.
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