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PHGY 314 > Lomber > Flashcards

Lomber Flashcards

1
Q

From a top view of the cortex, do we see mostly all of it?

A

NO
If we flatten the cortex, we get a surface area about the size of a dining room table → folded into sulci and gyri

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2
Q

Which brain cortices are found on directly on both sides of the central gyrus?

A

Somatosensory cortex (Posterior)
Motor cortex (Anterior)

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3
Q

What is the definition of plasticity?

A

It is the ability to be moulded and shaped
We will talk specifically about → Neuroplasticity/Brain plasticity
- Can also have periphral nervous system plasticity → can induce changes in the CNS
- Structure and functions are not static over time
- Greatest when young, decreases over time, but never disappears

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4
Q

Who did the idea of plasticity come from?

A

William James (a North American psychologist and philosopher)

Brain functions are not fixed throughout life

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5
Q

What is Kennard Principle?

A

*From margaret Kennard

There is a negative linear relationship between age at which a brain lesion occurs and the outcome expectancy → better chances of arrange the effect of a brain lesion earlier in life than later

Explained by the fact that in younger brains, there is more potential for compensatory plasticity

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6
Q

What is our definition of cortical plasticity?

A

Cortical plasticity = Changes that occur in the function and organization of the cerebral cortex as a consequence of experience

Experiences in this case is the presence of absence of a sense (stimuli)

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7
Q

What is cortical reorganization?

A

It is the fact that the brain will adjust itself to use the available tissue and not let space be wasted

Peripheral and central damage forces the brain to adapt and reorganize

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8
Q

What are the 5 examples of cortical plasticity we study in this class?

A
  1. Visual system → early development (occular dominance columns)
  2. Somatosensory system → early adulthood (owl monkey)
  3. Motor cortex → maturity
  4. Crossmodal plasticity → early development (1 sensory system affecting another, ex the loss of one allowing more space for another, Anterior Ectosylvian sulcus)
  5. Visual system → adulthood (stroke + caffeine)
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9
Q

How are occular dominance column an example of plasticity in early development?
(NOT autoradiography experiment)

A

In early development, there is no segregation of input form different eyes (layer IV is just mixed/unorganized synaptic terminals)

Later in development, LGN neuron terminals are arranged into occular dominance columns in layer IV of V1

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10
Q

Where in the visual pathway does information from both eyes come together for the 1st time?
How did they assess this experimentally?

A

At V1, because at the LGN it is still separated

  1. Injected radioactive proline into 1 eye → taken up by the RGCs
  2. Goes through optic nerve → LGN
  3. Goes all the way to V1
    *Different layers of LGN correspond to different eyes
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11
Q

What was observed in Layer 4 of V1 by autoradiography?
What was observed when they raised monkeys with one eye shut?

A

There are typical stripes in mature V4 corresponding to alternating input form one eye (pale stripes) and the other eye (darker stripes)

Almost complete takeover of the V1 space by the only active eye (seen by injecting it with the tracer and doing autoradiography → almost no black stripes)

They could go back and forther in cortical area by opening the shut eye and shutting it back until the end of the critical period where there is nto enough plasticity anymore

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12
Q

Is plasticity possible in adulthood?

A

It is possible, but much harder than earlier in development

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13
Q

Are all area represented equally in the somatosensory cortex and motor cortex mapping? What about the motor cortex?

A

Face and hand are overrepresented

*Motor cortex and somatosensory cortex are almost mirror of each other

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14
Q

Why are Owl monkeys are good model to study somatosensory plasticity?

A

They have a smooth brain → easier to look at their cortex

  • They have 5 areas corresponding to the 5 digits (fingers)
  • After repeated stimulation of the tip of the index, the area corresponding to it increased in size
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15
Q

Which are the 2 possible outcomes of the loss of a finger?

A
  1. Other neurons expand to fill the spaces where the neurons for that finger reside
  2. The area for the finger goes silent (no activity)
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16
Q

What was the effect of the loss of digit 3 on the monkey’s somatosensory cortex?

A

D2 and D4 cortical areas expanded into the space that was D3 (now unutilized)
- D2 and D4 became hypersensitive (behavioural advantage)

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17
Q

What was the effect of training a monkey’s D2 and D3 to discriminte between different stimuli ? (on its somatosensory cortex)

A

Caused cortical expansion of D2 and D3 (due to overstimulation)
- Overall hand cortical area didn’t expand

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18
Q

What are the changes in somatosensory cortex observed after hand amputation in maturity?

A

The area the was assigned to hand is taken over by upper arm/trunk/leg and by face (which are the neighbouring areas)

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19
Q

What experiment was done to assess motor cortex plasticity with training?

A

A monkey was trained on a task that required fine digit manipulation
- Cortical representation of digits expanded
- Shrinkage of forearm representation
- Total cortical territory did not change in size

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20
Q

What experiments did Rauschecker do to study crossmodal plasticity?
What was its conclusion

A

Studied Anterior Ectosylvian Sulcus → 3 unimodal fields in close proximity to each other:
Somatosensory (S4) + Visual (AEV) + Auditory (FAES)

CONCLUSION: Blind cats (eyelid sutured) showed that their visual fields became acoustic in the sulcus → removal of a sense causes cross-modal plasticity
→ Blind cats show better auditory spatial localization

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21
Q

What experiments/observations did Sur do about sensory substitution in the Auditory cortex?

A

Made lesion that could not occur naturally in ferrets (born with less developped brain)
- Inferior colliculus → no auditory input to the MGN
- Removed visual cortex → caused degradation of LGN

Results:
Retina sent axons → MGN → followed its path to the auditory cortex which became visuo-responsive (open synaptic space filled)

22
Q

What is pruning?

A

The process of removing neurons and processes that are not needed to make more space for the ones that are useful
*Follows Hebbian plasticity

23
Q

What is apoptosis in the context of cortical plasticity?

A

It is a form of cell death that is normal in development and enable the cells to die without affecting adjacent neurons → it allows pruning
- Cleaning event, allows other neurons to fill that space

24
Q

Why are pruning and apoptosis required for proper function of the brain and for cortical plasticity?

A
  1. Neurons compete for limited space
  2. They also compete for the ressources to survive
  3. In development, you want to birth more neurons than needed and make more connections to multiple different regions → get rid of the ones that turn out to be useless
25
Q

What experiment showed that caffeine (stimulants) can shrink scotomas?
*By inducing more synaptic activity

A

38 yo professor worke up one day and everything looked dimer (light)
- Realized it was a problem in the brain because information from both eyes was affected
- Was a stroke of the occipital (visual) cortex on the left hemisphere covering V1 and larger
- Affected the Upper-left quadrant of each eye
- Was able to shrink the area of the scotoma by drinking lots of coffee

26
Q

What experiment allowed to conclude that there was parallel processing/ventral and dorsal stream in the VISUAL system?

A
  1. 2 groups of monkey → 1 lesioned in the ventral pathway and 1 lesioned in the dorsal pathway
  2. Teach them both Object discrimination and Landmark discrimination task

Result:
Temporal (ventral) lesion → impairment in object discrimination task, but not the landmark discrimination task
Parietal (dorsal) lesion caused impairment in the landmark discrimination Task
*Double dissociation

27
Q

In the experiment in which they were trying to determine functional implications of dorsal vs ventral visual pathways of information processing in monkeys, what was the object discimination task?
What was the landmark discrimination task?

A

Object discrimination task:
Show monkey an object → take it away → show another object → identify if it is the same of not
Reward given following right answer

Landmark discrimination task:
Monkey need to tell if the cylinder is closer to left or right sides by chosing the food reward oon the same side as the object

28
Q

Which 2 auditory brain area were studied to better understand parallel processing in the auditory system?
(same idea as ventral/dorsal pathways of the visual system)

A

AAF → anterior auditory field → WHAT
PAF → posterior auditory field → WHERE
*Both receive direct projections from A1

29
Q

What 3 tests did they do on cats to test parallel auditory processing?

A
  1. Acoustic spatial localization → tests the where function
  2. Auditory pattern discrimination → tests the what function
  3. Acoustic detection task → negative control task (not testing for what or where function)

They examined 3 cats bilaterally implanted with cooling loops over AAF anf PAF auditory fields → turned off individually and reversibly

30
Q

What are different types of permanent neural deactivation?
Why are permanent methods important?

A
  1. Physical ablation
  2. Chemical (neurotoxins) → injected into the brain to destroy neurons
  3. Electrolytic → reverse the current using electrodes → burns the brain

Permanent methods are important because they tells us about the plastic changes that occur after a permanent lesion

Disadvantage → uses large amounts of animals + variability between animals

31
Q

What are reversible methods of neural deactivation?
What is the advantage of a reversible method?

A
  1. Chemicals:
    - Lidocaine → anesthetic
    - Muscimol, GABA → increase amount of inhibition to turn the area off
  2. Thermal:
    - Thermoelectric-Peltier → cooling plates on the brain
    - Cryoloops

Advantage: you can get experimental and control data from the same animal

32
Q

What is the mechanisms behind the Cryoloop technique?

A
  • Coolant = Methanol
  • Loop is put on a specific part of the brain
  • Thermocouple monitors the termperature (computer)
  • Computer controls the pump → changes the velocity of the methanol going through the loop to control temperature (faster = colder)
    Methanol reservoir → Pump → Ice bath (78.4˚C) → Cryoloop

~ 3˚C is enough to cool the full thickness of the cortex
*To reverse this process, you can let the brain warm up on its own

33
Q

How does reversible cooling deactivation affect neurons?

A
  • Tissue temperatures < 20˚C eliminate synaptic transmission (neurotransmitter release)
  • Disrupts Calcium uptake in the axon terminal
  • Doesn’t impair axonal transmission → myelin is a good insulator (axons must be cooled much more than cell bodies to stop transmission)
  • Highly localized
  • can be induced or reversed in minutes
  • Each animal serves as its own control
  • Multiple cortical sites can be examined in the same animal (multiple cryoloops)
34
Q

What is the protocol of the Acoustic Orienting Sound Localization task?
What where the results?

A

*Tests the “where” function of the auditory processing

Animal stands in an arena and every 15˚ around it, there is a speaker, a LED and a food reward port
1. The LED at 0˚ flashes on to bring the cat’s attention to the center
2. One of the speakers turn on and the animal has to go to the food port to get the reward

Results:
PAF bilateral deactivation → very bad performance
AAF bilateral deativation → no impairment (not involved in spatial localization)

*Even with PAF lesion, the could discriminate it the sound came from right or left hemifield, just not which port

35
Q

What is the protocol of the Acoustic Pattern Discrimination task?
What where the results?

A

*Tests the “what” function of the auditory processing

Animal is taught to discriminate morse code sequences
1 sequence plays, if the next sequence is the same, then the cat goes to the circle and if it’s different it must fo the the square (room divided into 2)

Results:
- AAF bilateral deactivation/cooling → impaired pattern discrimination
- PAF bilateral deactivation → no effect on the task

Had to confirm they could actually hear the sound with the AAF deactivation because AAF got it right 50% → Detection task → they confirm they could here it

36
Q

What is the detection task that was used to confirm that cats with AAF deactivation could actually hear the sounds, they could simply not discriminate when it changed?

A

Detection task:
1. Play a sequence once
2. Play the same sequence or Not → cat has to discriminate if it played or not

AAF and PAF deactivation showed no impairment

*They also checked that cooling didn’t cause cell damage or cell loss

37
Q

What experiment was done to assess if there is a sound descrimination pathway in the Auditory cortex?
(Complex sounds, not just pattern discrimination)

A

Played pure tone, broadband noise and human vowel sound (more and more complex)

They imaged the brain and saw activation in the auditory cortex:
- Largest area stimulated for vowels (most complex)
- Smaller area stimulated for BPN
- Smallest area stimulated for PT

38
Q

What is the “what” pathway of the auditory cortex?

A

A1 → A2 → IN + T

39
Q

What are the conclusion of the experiment where the stimulate with pure tone (PT), broadband noise (BPN), vowels (VOW)?

A

In the visual system, specificity for increasingly complex visual stimuli is found along the visual cortex in the temporal lobe (V1 → IT)

In the auditory system, specificity for increasingly complex acoustic stimuli is found along the auditory cortex in the temporal lobe (A1 → T + IN)

Area T is critical for the accurate discrimination of conspecific vocalization (species specific)
→ Unilateral deactivation (cryoloops) of left but not right area T results in deficits during conspecific vocalization discriminations

Experiment:
Play 2 sounds and have to discriminate if the 3rd it the same or not

The more complex the stimulus was, the faster the performance was considered good (faster learning)

40
Q

What is an example of critical perdiod in visual system?

A

The Lazy eye situation, where the patch works much better in kids, not worth it for adults

41
Q

What is DZ responsible for in normal cats?

A

DZ is responsible for acoustic motion processing (leftward motion vs rightward motion)
→ In deaf animals, becomes visual motion detection

42
Q

What was seen in the experiment in which they deactivated PAF vs DZ in deaf cats?

A

VISUAL double dissociation in the auditory cortex:

Visual detection in the peripheral field → impaired in PAF deactivation (not affected by DZ deactivation)

Detection of movement (visual) → impaired by DZ deactivation (on affected by PAF deactivation)

43
Q

What is the supramodal hypothesis?

A

Cortical areas that have been physiologically reorganized in response to sensory loss (deafness/blindness) will be involed in behaviours that are similar to those of hearing/sighted subjects, but are mediated by the replacement modality

44
Q

What is seen in the experiment in which they discriminate pure tone, broad band noise and vocalizations when A1 is cooled vs A2 vs IN vs T?

A

A1 cooled → deficits in all 3
A2 inactivated → only affects noise and vocalization discrimination (not tone)
T incativated → only affects vocalization discrimination
IN → no effect

*Information goes from A1 → down

45
Q

Why are cats a goodl model of hearing and deafness?

A
  1. Have auditory system that is similar to that of humans:
    cochlea → brainstem → midbrain → thalamus → auditory cortex
    - Only difference is movable pinna et hear much higher frequencies
  2. Cats are highly acoustic (nocturnal)
  3. 20% of their cerebrum is acoustic
  4. Auditory cortex is easily accessible
  5. They eat rodents
  6. Large literature available
46
Q

What are the main parts of a cochlear implant?
What areas did they look at following cochlear implant installation?

A

External Components:
- Microphone → Captures sound from the environment.
- Sound Processor → Processes the sound into digital signals. Breaks the sound into frequency-specific components.
- Transmitter Coil → Sends the processed signals wirelessly to the internal implant through radiofrequency transmission.

Internal Components:
- Receiver-Stimulator → Surgically implanted beneath the skin.
Converts the digital signals into electrical impulses.
- Electrode Array → Inserted into the cochlea. Delivers electrical stimulation to the auditory nerve at specific locations corresponding to different sound frequencies.
*Magnetic so not fMRI safe

Looked at areas 41 and 42
How good is the cochlear implant at expanding A1 and does it affect other auditory areas?

47
Q

Do deaf see better?

A

Yes and No → No general improvement in vision for deaf people, but do have better visual abilities for some features
Better at 3 things:
- Visual orienting and reorienting
- Visual motion processing
- Visual stimulus onset detection

48
Q

What animal model was used to study deafness?

A

Deaf cats:
- White fur + 2 blue eyes → 80% chance they are deaf
- not albino or siamese
The phenotype is so specific that if the cat has one blue eye and one brown eye, they will hear from the side with the brown eye, but be deaf on the other side (deaf from ear ipsilateral from blue eye and hear in ear ipsilateral from brown eye)  unilaterally deaf

→ Deaf phenotype is confirmed with Auditory Brain response at 1 month (click stimulation)
After maturity (~1 yo), they start training them on different tasks + implant cooling loops → total of 5 years/animal

49
Q

In the auditory brain response test on blind cats, when do we see a little blip?

A

No response at all, until hit the

Sound is so loud the cat can feel its vibrations → ~125dB (tactile sound level)

50
Q

What different tests were done to determine if visual abilities are enhanced as a consequence of deafness?

A

Used the 2 alternative dorced choice task method (easy at the start and gets harder) with deaf vs hearing cats

Visual Psychophysical tasks:
- Vernier acuity (visual accuracy, 1 broken line)
- Grating acuity
- Orientation discrimination
*No differences between 2 populations for these tasks

  • Direction of motion discrimination
  • Velocity of motion discrimination
    *No differences between 2 populations for these tasks
  • Detection of movement
  • Detection across the visual field/in peripheral field
    *Significantly better performance by deaf cats

*Note that the acuity task measures how sharp the vision is

51
Q

Which 2 visual tasks did congenitally deaf cats do better on than hearing cats?

A
  • Detection of movement
  • Detection across the visual field/in peripheral field
52
Q

What 4 zones of the auditory cortex did they study when wanting to determine what role the “deaf” auditory cortex may play in mediating the superior visual functions identified in aim 1.
*Aim 1 showed that deaf cats did bettern on movement detection and

A
  • AAF
  • A1
  • PAF
  • DZ (Dorsal Zone)
    *With reversible cooling loops → first deactivated all 4 to make sure they would see a significant change between (deaf + inactivation) vs (deaf)

PHGY 314 (9 decks)

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