Lomber

Question 1

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

Answer 1

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

Question 2

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

Answer 2

Somatosensory cortex (Posterior)
Motor cortex (Anterior)

Question 3

What is the definition of plasticity?

Answer 3

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

Question 4

Who did the idea of plasticity come from?

Answer 4

William James (a North American psychologist and philosopher)

Brain functions are not fixed throughout life

Question 5

What is Kennard Principle?

Answer 5

*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

Question 6

What is our definition of cortical plasticity?

Answer 6

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)

Question 7

What is cortical reorganization?

Answer 7

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

Question 8

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

Answer 8

1. Visual system → early development
2. Somatosensory system → early adulthood
3. Motor cortex → maturity
4. Crossmodal plasticity → early development (1 sensory system affecting another, ex the loss of one allowing more space for another)
5. Visual system → adulthood

Question 9

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

Answer 9

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

Question 10

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

Answer 10

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

Question 11

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

Answer 11

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

Question 12

Is plasticity possible in adulthood?

Answer 12

It is possible, but much harder than earlier in development

Question 13

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

Answer 13

Face and hand are overrepresented

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

Question 14

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

Answer 14

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

Question 15

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

Answer 15

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)

Question 16

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

Answer 16

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

Question 17

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

Answer 17

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

Question 18

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

Answer 18

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

Question 19

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

Answer 19

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

Question 20

What experiments did Rauschecker do to study crossmodal plasticity?

Answer 20

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

Blind cats (eyelid sutured) showed that their visual fields became acoustic in the sulcus → removal of a sense causes cross-modal plasticity

Question 21

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

Answer 21

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)

Question 22

What is pruning?

Answer 22

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

Question 23

What is apoptosis in the context of cortical plasticity?

Answer 23

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

Question 24

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

Answer 24

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

Question 25

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

Answer 25

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

Question 26

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

Answer 26

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

Question 27

In the visual parallel stream experiment, what was the object discimination task?
What was the landmark discrimination task?

Answer 27

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

Question 28

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)

Answer 28

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

Question 29

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

Answer 29

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

Question 30

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

Answer 30

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

Question 31

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

Answer 31

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

Question 32

What is the mechanisms behind the Cryoloop technique?

Answer 32

• 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

Question 33

How does reversible cooling deactivation affect neurons?

Answer 33

• 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)

Question 34

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

Answer 34

*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

Question 35

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

Answer 35

*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

Question 36

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?

Answer 36

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

Question 37

What experiment was done to assess if there is a sound descrimination pathway in the Auditory cortex?

Answer 37

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

Question 38

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

Answer 38

A1 → A2 → IN + T

Question 39

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

Answer 39

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 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)