Exam 3: Topic 9

Question 1

when do humans have the most plasticity?

Answer 1

right after birth there is an explosion of dendrites and then pruning occurs
- The human brain has 100 billion neurons, 600 trillion synapses (adults), and 1,000 trillion (quadrillion) synapses in young children

Question 2

what phenomena occur during development of the nervous system? (4)

Answer 2

• Formation of brain regions
• Neurogenesis
• Axonal growth
• Synaptogenesis

Question 3

what are critical periods and modification to brain circuits based on?

Answer 3

experience

Question 4

neural activity

Answer 4

sensory input and sensorimotor integration that allows adaptation and triggers the refinement of connections via calcium, neurotrophins, local gene expression, cytoskeleton, etc.

Question 5

T/F Many basic physiological processes are innate or hardwired and require no experience

Answer 5

True
- like brainstem neural control of respiration
- For many behaviors there are specific points in the lifetime of the organism in which these behaviors can be learned

Question 6

what do complex behaviors require?

Answer 6

neural activity for development

Question 7

how do genetics influence brain circuits?

Answer 7

prenatal construction of neuron circuits and their highways are genetically specific and therefore controlled by genes

Question 8

what are postnatal modifications of neuron circuits? (2)

Answer 8

• Adapt to changing external environments
• Temporal windows for the brain to become refractory to the lessons of experience ⇒ critical or sensitive periods

Question 9

critical period

Answer 9

represents the limited times of postnatal development change elicited by electrical activity in specific circuits
- system, circuit, or cell waiting for specific instructional information from the environment

Question 10

postnatal experience

Answer 10

patterns of neural activity

Question 11

T/F If appropriate experience is not gained during the critical period, the pathway may still attain the ability to process certain forms of sensory information?

Answer 11

False it may never attain ability
- depth of an object, perception, etc. may be impaired permanently

Question 12

T/F during a critical period the system can adapt to virtually any stimuli, appropriate or inappropriate?

Answer 12

True

Question 13

how is it possible to delay/accelerate the critical period? (2)

Answer 13

1. Environment via dark rearing
2. Molecules via GABA

Question 14

built in behaviors

Answer 14

experience is an on switch for these behaviors and will develop when prompted by the environment
- auditory, vision
- olfactory is more evolutionarily primitive

Question 15

what are properties of critical periods? (9)

Answer 15

1. Duration is proportional to lifespan
2. Functional competition between inputs
3. Neuronal activity ⇒ action potentials, forward and back propagating
4. Structural consolidation of pathways
5. Onset and duration is defined by neural activity
6. Different critical periods for different systems
7. Diversity of sensory/motor systems and molecular mechanisms
8. Particular roles of excitation and inhibition ⇒ GABA can close the critical period
9. Potential for reactivation ⇒ training, growth factors

Question 16

congenital blindness

Answer 16

no neuron machinery to make light photons into electrical impulses and cannot gain vision

Question 17

how does congenital blindness and braille reading affect neurons?

Answer 17

the back of the head has the visual cortex which lights up when looking at things and the primary visual cortex lights up when braille is done ⇒ not a use it or lose it situation
- The neocortex is very opportunistic and will use tissue for different purposes

Question 18

how do blind vs not blind people have impacted memory performance?

Answer 18

superior verbal memory in congenitally blind subjects
- about 0.5% to 2% change in memory

Question 19

who won the Nobel prize for discovering ocular dominance and brain plasticity?

Answer 19

Hubel and Weisel
- showed high plasticity immediately after birth and importance of rich stimuli to our brains

Question 20

what is the path from the eye to the brain?

Answer 20

retina => optic tract ==> LGN => optic radiations => V1
- the primary visual cortex receives direct input from the visual thalamus

Question 21

where does visual dependent plasticity occur?

Answer 21

in the V1 Cortex area not the retina or thalamus

Question 22

are retinal neurons monocular or binocular? Thalamic? Cortical?

Answer 22

monocular; monocular; binocular

Question 23

monocular

Answer 23

each of the two eyes are not interconnected

Question 24

what layers are the binocular vs monocular cells in?

Answer 24

monocular are in layer 4 while binocular are in layer 2+3

Question 25

ocular dominance columns

Answer 25

Axons from cells in the lateral geniculate nucleus serving each eye terminate in separate bands in layer 4 => these bands appear to alternate for left vs right eyes

Question 26

how do you identify synaptic targets of information from the retina via ocular dominance columns?

Answer 26

inject radiolabeled amino acid proline into one eye and it will get incorporated into proteins and be transported across synapses - See radioactive label (white) in specific areas of layer 4 in the visual cortex - Dark areas are visual cortex that receives information from the unlabeled eye

Question 27

T/F in typical adults, each eye has about equal territory of synapses in layer 4 relating to neurons for vision?

Answer 27

True

Question 28

what happens to deprived eye columns after monocular deprivation?

Answer 28

eye columns are shrunken, not disappearing ⇒ competitive imbalance - even with temporary eye closure there is still an effect - light patches are non-deprived eye and these columns have expanded compared to the other side

Question 29

T/F eyelid closure means that neural activity in that eyes retina goes to zero?

Answer 29

False - There is still spontaneous neural activity in that deprived eye

Question 30

how does monocular deprivation affect terminal arborizations?

Answer 30

in the LGN axons of the visual cortex, short term monocular deprivation and long term monocular deprivation both lead to less axon synapses on receiving cells - the cells look much less dense and have fewer projections

Question 31

T/F the ocular dominance assay rapid test where one eye is covered can cause monocular deprivation?

Answer 31

False its a rapid test that takes seconds to minutes not days - It alone does not induce plasticity

Question 32

what would neurons in layer 4 show up as on a histogram? Layer 2/3?

Answer 32

they would likely be more toward the edges of the histogram - the layer 2/3 neurons are more in the middle as they will have a converged response from both eyes

Question 33

how does monocular deprivation affect ocular dominance histograms?

Answer 33

it shifts the activated cells to either the ipsilateral or contralateral sides of the graph depending on where the electrode probe is placed in the brain - Whether it shifts ipsilateral vs contralateral depends on which eye is patched and which eye is recorded ⇒ get contralateral if recorded from opposite hemisphere

Question 34

when monocular deprivation occurs which eye do most of the cells respond to?

Answer 34

they respond to the eye that has not been covered - we only see action potentials from the eye that is always open - the synapses left over are not sufficient to drive past spike threshold and make the neurons fire

Question 35

T/F Even 1 day of monocular deprivation can produce a shift in ocular dominance in a cat?

Answer 35

True

Question 36

T/F there is a shift in the ocular dominance histogram if monocular deprivation occurs in adult mammals?

Answer 36

False only during the critical period

Question 37

T/F there are competitive imbalance inputs with binocular deprivation?

Answer 37

False there are no competitive imbalances as they are both unstimulated

Question 38

what drives ocular dominance plasticity?

Answer 38

competition and local correlations in neural activity - even weak deprivation can produce a catastrophic shift

Question 39

what pattern do we see regarding monocular deprivation and hebbian plasticity?

Answer 39

normally there are inputs to a neuron coming from both left and right cells, but when there is deprivation in one eye those inputs no longer come in - the other inputs from the open eye will begin to cooperate and after a certain point the outcompeted inputs will not turn back on

Question 40

what competition occurs in strabismus?

Answer 40

strabismic animals and humans will see with one eye at a time to prevent double vision and corrupted vision so inter-ocular conflict occurs from a lack of binocular convergence - if two different stimuli are presented to each eye, the visual system gets confused and will shut down thalamic afferents from one eye - Every 5-8 seconds your perception will switch from one eye to the other (binocular rivalry)

Question 41

T/F the 2 + 3 cell layers will get strong inputs from both eyes during binocular rivalry?

Answer 41

False, none of the ⅔ layer cells will get strong inputs from both eyes at the same time - Very few respond to stimulation of both eyes - Not getting coincident input on the same cells - if one eye deviates from the other eye fixating at a certain point, there is a constant conflict

Question 42

what happens when you block NMDA receptors in the visual cortex during the critical period?

Answer 42

leads to a blocking of a shift in ocular dominance plasticity and changes dendrite structure without gene expression - signaling to the nucleus is calcium dependent for gene expression and synaptic plasticity in general - calcium will not enter the cell and thus synaptic cell activity will be halted

Question 43

what ocular experiment confirmed hebbs postulate?

Answer 43

when a third eye was inserted into a frogs head on one side of the face, there was originally no competition between the two tectum regions in the brain, and then competition occurred on the opposite side of the brain where the transplanted eye and normal eye were located - this led to an appearance of alternating columns for vision just like in higher mammals brains

Question 44

how was ocular dominance plasticity tested in rats? Including the dark exposure?

Answer 44

rats underwent monocular deprivation during their critical period and then were taken swimming to find a hidden platform using visual cues - dark exposure therapy for 10 days somewhat recovered the deprived eyes vision but impacted the rats visual acuity - for rats who did not do dark exposure they had no recovery and could not find the hidden platform - went from about 0.2 acuity to 0.6 acuity compared to 0.8 acuity for non deprived rats

Question 45

closely spaced lines demonstrate what aspect of visual frequency?

Answer 45

high spatial frequency

Question 46

widely spaced lines demonstrate what aspect of visual frequency?

Answer 46

low spatial frequency

Question 47

T/F there is a competitive imbalance between two eyes for cortical territory with bilateral cataracts?

Answer 47

False there is no competitive imbalance for people who have bilateral cataracts - Ocular dominance should be perfectly normal but other plasticity has been affected

Question 48

what side effects do people with bilateral cataract removal during adulthood have?

Answer 48

contrast boarders in objects are treated as independent instead of as a whole object - such as spots on a cow each being their own object - they have object and "figure from ground" blindness

Question 49

what does exposing a young mouse to a single tone frequency result in?

Answer 49

the expansion of the territory in which auditory cortical neurons are responsive to that tone, at the expense of the representation of other tones with lower or higher frequencies - When having prolonged exposure to a certain frequency during the critical period there will be more neurons in that particular frequency auditory cortex

Question 50

what is the difference in hand babbling for deaf infants vs normal hearing infants?

Answer 50

deaf infants raised by deaf parents using ASL compared to hearing babies will use more babbling with their hands and fingers to replace vocal babbling in hearing infants

Question 51

how does age affect learning a language when immigrating somewhere new?

Answer 51

immigrants learning english have an easy time prior to the age of 3 but afterward there is a steady decline in ability to learn and speak like a native speaker

Question 52

end card

Answer 52

hehe :)