Chapter 24 - Modification of neural circuits as a result of experience

Question 1

What is Hebb’s postulate?

Answer 1

In 1949, the psychologist, David O. Hebb hypothesized that the coordinated activity of a presynaptic terminal and a postsynaptic neuron strengthens the synaptic connection between them. This has come to be known as Hebb’s postulate.

Question 2

What is a critical period?

Answer 2

Critical periods are temporal windows where experience and neural activity that reflects that experience has maximal effect on the acquisition or skilled execution of a particular behavior.

Question 3

Give an example of a critical period in animals.

Answer 3

Imprinting in hatchling birds.

Question 4

Give an example of a critical period in humans.

Answer 4

The acquisition of language.

Question 5

Hubel and Wiesel sutured the eyes of a kitten, depriving it from any sensory stimulation by one eye. When the suture was later opened, how did this affect the cat’s vision?

Answer 5

Previous work had indicated that the ocular dominance columns responded differently to stimuli from either eye. The columns respond on a continuum between only one eye and both eyes. This normal distribution of ocular dominance at the level of single cortical neurons was shown to be alterable by experience. While the recordings from the retina and the LGN of the cat indicated that these pathways were working normally for the sutured eye, their recordings from the visual cortex indicated that the ocular dominance distribution was shifted when compared to a normal population.

Question 6

Suturing one eye of a kitten results in “cortical blindness” - amblyopia, in the adult cat. Even if the formerly deprived eye remains open, little or no recovery occurs. What happens if the same is done with an adult cat?

Answer 6

If one eye of an adult cat was closed for a year or more, both the ocular dominance distribution measured across all cortical layers and the animal’s visual behavior were indistinguishable from normal when tested through the reopened eye.

Question 7

Experiments of monocular deprivation in monkeys has revealed similarities or differences from studies on cats. Which?

Answer 7

Most results are similar, but the critical period is longer in primates.

Question 8

Results from mocular deprivation studies suggest competitive interaction between the two eyes during the critical period. What is meant by competitive interaction?

Answer 8

That they compete for brain matter. The cortex that would process the deprive eye instead is used to process the open eye.

Question 9

The loss of acuity, diminished stereopsis, and problems with fusion that arise from early deficiencies of visual experience is called …

Answer 9

amblyopia.

Question 10

The loss of acuity, diminished stereopsis, and problems with fusion that arise from early deficiencies of visual experience is called amblyopia. In humans, amblyopia is most often the result of …

Answer 10

strabismus (skjeling).

Question 11

What causes strabismus?

Answer 11

Striabismus is usually caused by damage to the extraocular muscles.

Question 12

How common is striabismus?

Answer 12

About 5% of children.

Question 13

How do people with striabismus adapt to the condition?

Answer 13

By an unknown mechanism that seems to suppress one eye, causing one of the them to become dominant. Functionally, the suppressed eye eventually comes to have very low acuity and may render and individual effectively blind in that eye.

Question 14

What happens if both eyes are blocked during the critical period?

Answer 14

When opened again, this has less a dramatic effect than for monocular deprivation. It seems that the difference in competition between the two eyes is more significant than the amount of stimulation to the eyes.

Question 15

Is there a critical period for more advanced behaviors?

Answer 15

Probably, yes! For instance, language in humans.

Question 16

What is manual babbling?

Answer 16

Infants begin producing speechlike sounds at about 7 months. Deaf children do not, and this seems to affect their language skills. However, if exposed to sign language these deaf children start babbling with their hands - manual babbling.

Question 17

Critical period for phonemes. When is this?

Answer 17

Very young human infants can perceive and discriminate between differences in all human speech sounds, and are not innately biased towards phonemes characteristic of any particular language. By 6 months of age, however, infants begin to show preferences for phonemes in their native langauge over those in foreign languages. By the end of their first year, they no longer respond robustly to phonetic elements that are peculiar to non-native languages.

Question 18

Observations in the 1980s gave insight into a possible cellular basis for activity-dependent plasticity and critical-period phenomena throughout the cerebral cortex. Which observations?

Answer 18

The observations that the number of synapses increased during prenatal, and a limited period of postnatal life, declined during a protracted period that included much of adolescence, and reached a steady state in early adulthood.