OV2023 visual perception > Retinal Projections: Parallel processing pathways > Flashcards

Retinal Projections: Parallel processing pathways Flashcards

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1
Q

What does the main optic pathway begin with ?

A
  • retinal ganglion cells, their cell bodies and dendrites in the retina - ganglion cells give rise to axons that travel to the brain , first in optic nerve, pass through optic chiasm , into optic tract
  • end up making direct synaptic connections of excitatory nature with neurons in the LGN of the thalamus
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2
Q

What are the 3 classes of retinal ganglion cells that form parallel processing input from retina to LGN?

A
  1. Midget/Parvo: Detailed Form VISION /High Acuity & Colour with (Red/Green)
  2. Parasol/Magno: Global Forms /Low Acuity & Motion Vision
  3. Small Bi-Stratified/Konio: Colour (Blue/Yellow)
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3
Q

What do some retinal ganglion cells that have no involvement in Visual perception do ?

A

they send their axons to non -geniculate nuclei outside the thalamus

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4
Q

What are the 4 other classes of ganglion cells associated with other divisions of labour which mediate visual reflexes?

A

Circadian Rhythms; Pupillary Light Responses; Eye Movements

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5
Q

What is the major sub-class of our retinal ganglion cells ?

A
  • The ‘Midget’ or Parvocellular

- 80% of our ganglion cells are this

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6
Q

What are some anatomical properties of the parvocellular ganglion cells?

A
  • Small cell bodies, short dendrites, small diameter axons
  • Concentrated in central retina, fewer peripherally
  • Project to the Parvocellular layers (3-6) of LGN
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7
Q

What retinal ganglion cell sub class contributes to 10% of the cells ?

A

The parasol or magnocellular sub class.

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8
Q

What are some anatomical properties of magnocellular ganglion cells ?

A

-Large cell bodies & wide dendritic trees
-Wide diameter axons, heavily myelinated (fast conduction)
-Even distribution across central-to-peripheral retina
Project to Magnocellular layers (1 & 2) of LGN

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9
Q

What retinal ganglion cell sub class contributes to 5% of the cells ?

A

The ‘Small Bi-Stratified’ or Koniocellular sub-class

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10
Q

What are some anatomical properties of koniocellular ganglion cells?

A
  • Small cell bodies & wide dendritic trees, very thin axons(slow conducting system - not very myelinated)
  • Concentrated in central retina, few periphery
  • Project to Konio cells in ‘Inter-laminar zones’ of LGN
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11
Q

What are the functional properties of the parvocellular ganglion cells?

A

-Small receptive fields, sustained responses
-ON/OFF & OFF/ON
luminance/brightness and red-green contrasts
-Luminance: high spatial frequencies (fine detail) , low contrast sensitivity (need a high contrast stimulus to activate receptive fields )
-High acuity (‘detailed form’) vision & red green Colour processing

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12
Q

What are the functional properties of the magnocellular ganglion cells?

A

-Larger receptive fields, transient (brief) responses
ON/OFF & OFF/ON; luminance/brightness contrasts only (achromatic)- no involvement in colour processing
-Luminance: low spatial frequencies (low acuity ), high contrast sensitivity (if put low contrast in receptive field they will respond to it)
-Also: high temporal contrast sensitivity (i.e., respond well to flicker & image change)- important - as theses cells are particularly responsive to image motion - motion involves change in image location and magno are really sensitive to this
(( Low acuity (‘global form’) & Motion))

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13
Q

What are the functional properties of the koniocellular ganglion cells?

A

-Small receptive fields, sustained responses

NOT centre-surround or luminance; blue-yellow contrasts only

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14
Q

What does global form/ low acuity mean ?

A

-filtered images with fine detail (high spatial frequencies) removed (except at the block borders), as seen by the lower acuity Parasol or Magno-cellular System. Who are they?

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15
Q

What is the anatomy of CSF (contrast sensitivity function ) ?

A
  • formed by plotting the spatial frequency (cycles/degree) against Contrast sensitivity (reciprocal of the actual contrast of the grating)
    (example of looking at thumbnail)
    -1 cycle per degree is one white bar and black bar contained within thumb nail- low spatial frequency
    -30 cycles/per degreee- 30 whit black bars in thumbnail- is higher spatial frequency
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16
Q

how many cycles per dgreee do you see if you have a VA of 6/6?

A

30 cycles per degree ( 30 black and white bars)

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17
Q

What are the ranges in the CSF graph ?

A

at the start low CS to low spatial frequency
at the end low CS to high spatial frequency
-In the mid range -with high CS to spatial frequency forming the peak of CSF which is 6 cycles per degree for most people (Snellen of 6/30)
-graph usually looks like inverted U

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18
Q

How do you deduce this CSF?

A

SHOW Grating of one particular spatial frequency)- change contrast between the white and black bar of the single spatial frequency - then work out what the lowest contrast the px can see- then plot.

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19
Q

What is the difference between the midget and parasol type ganglion cells?

A

make different contributions to the anatomy of the CSF

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20
Q

Why is there a difference between the midget and parasol cells ?

A

their preferred spatial frequency of these 2 ganglion cell types approx match the size of the ON and OFF regions of their receptive fields

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21
Q

What are the midget cells like ?

A
  • Smaller Receptive Field Centres & Surrounds, are more responsive to higher Spatial Frequencies.
  • as indicated by the panel on slide show
  • the thin white bar will fill up the centre of the on centre might ganglion cells and 2 thin black bars fill up and surround the midget cell- will be the stimulus the cell really likes
  • thin white bar flunked by 2 thin black bars- means fine spatial detail - high spatial frequency
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22
Q

What are the parasol type ganglion cells like ?

A
  • Larger Receptive Field Centres & Surrounds, are more responsive to lower Spatial Frequencies
  • to get an on centre off surround parasol cell to fire maximally- need a wider white bar to fill up the centre and 2 wider black bars to fill up the surrounding side- the cell will get very excited
  • this means the parasol cells are more responsive to lower spatial frequencies in the visual image
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23
Q

What happens as the (C)entre-(S)urround RF (Receptive field) Sizes influence spatial frequency selectivity ?

A

the 2 ganglion cell types make different contributions to the overall CSF

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24
Q

What happens if you see a young child or adult who lost the ability to see the high spatial frequencies on the CSF?

A

BEEN An affect on the midget cells
-amblyopic person - this happens- VA drops if this condition is present - will lose VA on the high spatial frequency end of the - the midget and parvo cells affect this condition

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25
What does the plus sign mean in the centre ?
light on in the centre
26
What does the minus sign mean ?
darkness or light off in the surround
27
What is the response to light on in the centre for midget cells ?
is sustained -while light is on the cell continues to fire A.P - which vertical lines illustrate- fired by midget ganglion cell into centre
28
What is the response to light on in the centre for parasol cells ?
- gives only brief/transient response to light on | - rapid burst of A.P
29
What is the response to light on in the surround for midget cells ?
sustained response
30
What is the response to light on in the surround for parasol cells ?
transient response
31
What is the overall response of shining light in the centre of midget cell receptive field ?
light goes off and comes back on again -the midget cell is still responding to the first light- so if you shine 2nd light there will ben o response as it is already responding to first one
32
What is the overall response of shining light in the centre of parasol cell receptive field ?
can follow receptive stimultion- light going on and off | -means they have high temporal CS - able tor respond to things like flicker
33
What is the differences in temporal frequency tuning in midget and parasol cells ?
2 ganglion cell types presented with their preferred spatial frequency - Midget cell - high spatial frequency - Parasol cell- low spatial frequency - then turning that grating (that spatial frequency ) on and oFF a number of times per second - this response
34
Describe the test for the Differences in Temporal Frequency Tuning (at the preferred spatial frequency)(Derrington & Lennie, 1984) - in the powerpoint
- In midget cell : response of this- to that preferred spatial frequency being turned oN AND OfF AT THESE different temporal frequencies (Hz) - response of this midget ganglion cell peaks at 10x a second 10Hz per second then cuts off - has low CS - the best it could follow was 20Hz per second In the parasol cell - response to this - higher overall CS - has a peak at 10hz too - was able to follow low spatial frequency grating being switched on and off 50hz per second which is a really rapid flicker- much higher temporal frequency turning than midget cell.
35
What is the conclusion of the differences of the midget and temporal cell in temporal tuning ?
-the parasol cell can follow Fast Flicker & is also better for detecting image Motion (CRT/TV screens flicker @ 60Hz
36
What is the behavioural measure that looks at temporal frequency tuning in the human visual system ?
critical flicker fusion function (CFFF)
37
What does the CFFF do for a human ?
it cuts off at 50Hz - can follow 50 flickers a second but not changes in the image which are greater than 50Hz a second - that inability to follow changes in the image greater than 50Hz is exploited by Tv screens - the screen refreshes/flcikerds 60Hz a second. - a stationary image is presented on screen but its changing 60x a second but you cant follow that - so looks a little like motion - if watching Tv - flickering at a rate of 60Hz- a fly would be able to see all the stationary frame in the image because CFFF for fly is 300Hz. - can see a change in image 300 times a second.
38
What do the retinal ganglion cell sub classes do ?
all report info to the LGN - important to realise the LGN is not a random mass of cells- it likes order - there are 6 separate layers of neurons WITHIN the LGN]
39
What do the grey areas in the LGN image signify ?
the cell bodies of individuals neurons within the LGN
40
What does the bottom layers have in the LGN?
magnocellular layers 1 and 2
41
What is the in the magnocellular layers 1 and 2 in the LGN?
-have larger black dots in them compared layers 3-6
42
Why can we see the larger black dots in layers 1 and 2 in the LGN compared to the other layers ?
-this is because these 2 bottom layers of LGN contain large neurons (magno) and they receive direct input from the parasol type retinal ganglion cells (big cells)
43
What do the layers 3-6 contain in the LGN ?
smaller cells | -called parvocellular layers
44
What do the parvocellular layers 3-6 receive in the LGN?
these layers receive direct input from midget type retinal ganglion cells
45
What separates the 6 layers into distinct strata ?
bands of white matter
46
What does the white matter contain ?
- its axons of retinal ganglion cells that are trying to gain access to make synaptic connections with neurons in the layers 1-6 - also axons of the LGN NEURONS in these layers which are leaving the LGN and sending info up the visual cortex
47
What is the inter laminar zones?
between the major layers - little black dots that are scattered around here
48
What are in-between the layers 1-6 of the LGN?
-known as konio cells of LGN
49
Where are the konio cells in the LGN ?
- they are spotted and scattered around in amongst the white matter of the inter lamina zone - its those neurones which receive direct input from the small bi-stratified ganglion cells associated with blue yellow processing .
50
What are the major functions of the LGN ?
-seperate out and organise the inputs from the parvo, magno or konio cells into : - Function-specific layers (including the interlaminar zone) - Before sending the information on, still in parallel, to the Primary Visual (V1) Cortex in the Occipital lobe - activation which is Required for Visual Perception
51
What do the the neurons that reside in these diff layers and receive input from the P , M , K cells have?
``` have receptive fields which are very similar to those of the (P, M or K) retinal ganglions that supply their specific synaptic inputs -Except that the receptive fields of the LGN, are slightly larger than the ganglion cells which provide the input (due to convergence from several ganglion cells of one type) (because more than 1 ganglion cell of a particular class like a midget cell will connect to single parvocellular neurone in the LGN) & even less responsive to diffuse light (due to stronger ‘lateral’ inhibition in the LGN itself)- more contrast sensitive to ganglion cells. ```
52
What are the cells of the magnoceullaur layer are interested in the LGN?
- Global low acuity images | - in object motion
53
What are the cells of the parvocellular layers are interested in the LGN?
- high acuity vision | - red green colour contrast
54
What are the cells of the konio layer are interested in the LGN?
-blue yellow processing
55
What do the parasol ganglion cells do ?
-provide input to the magno cellular layers 1-2 forming the organ of the m pathway
56
What do the midget retinal ganglion cells do ?
provide input to neurons in the 3-6 LGN layers (parvocellular layer) and are the origins of the P pathway
57
What do the small bi stratified ganglion cells do ?
provide input to the konio cells in the inter lamina zones and a re the origins of the K pathway
58
What do each of these P, M , k pathways do?
send info up in parallel to the primary visual cortex | -end on different cells in different layers in V1.
59
Where are the midget retinal ganglion cells concentrated ?
in central retina.
60
Why do other retinal ganglion cell sub classes not involved in visual perception ?
because their axons do not project to the LGN
61
Where are the 2 ways that the RGC that are not involved in Vp go ?
1 - have axons that stop off earlier than the LGN - stop off at chiasm and make connections with the nucleus within the hypothalamus 2. Bypass the LGN into a white matter pathways at the end of the optic tract - called Superior brachium - those ganglion cells make connections with different nuclei in the upper mid -brain
62
What do some of these non-perceptual Parallel Processing Pathways include ?
from a very specialised type of ganglion cell that are photosensitive -Projections from specialized Photosensitive (melanopsin-containing in the cell bodies and dendrites) ganglion cells to the
63
What can melanopsin do ?
-capable of detecting and transducing light like rods and cones
64
What do these photosensitive ganglion cells connect to ?
a particular nucleus of the hypothalamus called | -Suprachiasmatic Nucleus - sits above the optic chiasm - receive direct input from these photosensitive ganglion cells
65
What are the types of photosensntivity they do ?
they are radiance detectors: Biological clock, circadian rhythms -great at determine whether its night or day
66
What is the importance of their input to the Suprachiasmatic Nucleus?
this is the location of our biological clock acitivity of our neurons in this nucleus determine our circadian rhythums -sleep/wake cycle -neurons change activity during the course of day and night
67
Why is it that the suprachiasmatic nucleus which contains biological clock needs to be told whether its night or day by these radians detecting photosensitive melanospin containing ganglion cells?
out biological clock does not run on a 24 hr cycle it runs on 25hr cycle - so it needs to be told by these ganglion cells when the day or night is over to entrain our circadian rhythms . - this is proven by taking uni students
68
What are the 3 parallel pathways to the upper midbrain from other photosensitive ganglion cells to the one nucleus ?
From other photosensitive-type ganglion cells (probably) to: - Olivary Pretectal Nucleus (OPT): for the pupillary light reflexes (constriction)- receives input from ganglion cells ``` & From other members of the small bi-stratified sub-class to: - Superior Colliculus (SC)(nuclei): for fast eye movements to novel stimuli- for looking around at diff objects- make fast head turn ``` - Accessory Optic Nuclei (AON): for optokinetic reflex during head motion Nothing to do with Visual perception
OV2023 visual perception
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