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Visual Science > Primary visual cortex: columnar systems > Flashcards

Primary visual cortex: columnar systems Flashcards

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1
Q

what are the names of the upper and lower part of layer 4C

A 
upper = 4c alpha 
lower = 4c beta
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2
Q

what do the cells of layer 4c beta go on to

A
  • blob cells

- inter blob cells

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3
Q

what do the cells of layer 4c alpa go on to

A
  • inter blob cells

- layer 4B

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4
Q

what do the cells from the konio pathway go on to

A

goes straight to blob cells (doesn’t go to layer 4C)

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5
Q

in relation to hubel & wiesel’s ice cube model, where does a single point in our binocular field of view which we can see by ganglion cells of both left and right eyes eventually end up

A

in a small region of the primary visual cortex with dimensions of 1mmx1mm

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6
Q

where do left and right eye ocular dominance columns go to

A

layer 4c

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7
Q

what type of connections do layer 4c cells have

A

prominent vertical connections with the neurons above and below getting input from the right and left eye, predominantly from these ocular dominance columns

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8
Q

what type of selectivity do the neurons in the ocular dominance columns have

A

orientation selectivity which respond preferentially to lines, contours, edges of a particular orientation within their RFs

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9
Q

what do cells rich in cytochrome oxidase form

A

polka dot blob pattern

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10
Q

what do primate ocular dominance column run up and down

A

the primary v1 cortex

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11
Q

what do we have pillar/columns of

A

cytochrome oxidase rich cells, with regions next to the cells which also have cytochrome oxidase, but not as much of it

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12
Q

what type of RFs of inter-blob cells have and what do they respond to

A

rectilinear RFs

which respond preferentially (maximally) to slits, lines, bars or edges = contours of a particular orientation

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13
Q

what do RFs of inter-blob cells not respond to

A

to all non-preferred (especially orthogonal) orientation of the same stimulus

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14
Q

what preference do vertical columns of inter-blob cells have

A

the same orientation preference

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15
Q

what preference do horizontally/across columns of inter-blob cells have

A

systemic preference changes ‘around the clock face’ so hates orientations that are not at 45 degrees but doesn’t mind orientations that are slightly off 45 degrees, even though its the same stimulus but orientation is wrong

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16
Q

list the three sub-types of orientation selective cells in these ocular dominance & orientation columns

A
  1. simple cells
  2. complex cells
  3. hypercomplex cells
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17
Q

how many % are there of simple cells

A

15%

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18
Q

how many % are there of complex cells

A

75%

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19
Q

how many % are there of hypercomplex cells

A

10%

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20
Q

which sub-type of orientation selective cells in these ocular dominance & orientation columns are most similar to ganglion and LGN cells

A

simple cells

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21
Q

which sub-type of orientation selective cells in these ocular dominance & orientation columns are least similar to the ganglion and LGN cells

A

complex cells

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22
Q

what type of sub regions do the simple cells have

A

spatially distinct
antagonistic
ON (excitatory) & OFF (inhibitory) sub-regions

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23
Q

as simple cells have ON (excitatory) & OFF (inhibitory) sub-regions, what shape are their RFs

A

Rsf are NOT circular, but are square or recti linear

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24
Q

what type of response do simple cells have with spots of light

A

weak

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25
Q

what type of response do simple cells have with stationary contours

A

strong

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26
Q

what type of summation and responses do simple cells have and why

A

linear summation

predictable responses, due to the sub-regions and due to amount of light falling onto the ON&OFF sub zone

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27
Q

why are their only a small minority of orientation selective cells have these types of RFs i.e. (15%) of simple cells

A

because their RFs resemble ganglion cells & neurons of the LGN

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28
Q

what type of RFs do complex cells have

A

larger RFs than simple cells with no spatially distinct ON or OFF sub-regions

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29
Q

what response do complex cells have to spots of light

A

none

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30
Q

what type of responses do complex cells have to stationary contours

A

weak

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31
Q

what type of responses do complex cells have to moving contours

A

better response than stationary contours

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32
Q

what type of responses do complex cells have and why

A

non-linear (unpredictable) responses, due to absence of sub-regions

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33
Q

how are complex cells responses non-linear and unpredictable

A

if the amount of light increases, response does not linearly correspond

34
Q

what type of of RF organisation do hyper complex sub-type cells have

A

simple or complex sub-types of RFs, but defining feature = silent inhibitory ‘end-stopped’ regions outside their main RF based upon lateral inhibition, makes them size selective & contrast & orientation

35
Q

what are hyper complex cells RFs influenced by

A

stimulus size, length as well as contrast & orientation

36
Q

what do all three sub-classes/types of orientation selective cells in the ocular dominance & orientation columns show

A

spatial frequency selectivity to grating stimuli i.e. some like low and some like high spatial frequency tuning

37
Q

how many types of range of different types of contour & form do simple cells particularly like

A

four types of ON & OFF RF sub regions in different simple cells
cross = ON responses to white light falling on the RF
triangle = OFF responses to dark regions falling on RF

38
Q

how are these four types of RFs of simple cells constructed in v1

A

convergent intra-cortical excitatory inputs from several neurons & local interactions within primary v1 cortex
i.e. if four neighbouring LGN cells all with ON-centre and OFF-surround RFs were to supply excitatory synaptic inputs to 1 simple cell, then it would acquire an oriented ON-centre RF with 2 similarly oriented OFF flanking surrounds, however there is no real evidence for this theory & intra-cortical inhibition

39
Q

what reduces/loses the orientation selectivity of area v1 cells

A

blocking inhibition by the presence of GABA-receptor blocker

40
Q

what happens when the GABA-blocker is removed

A

recovery

41
Q

what is the antagonist of GABA receptors

A

a drug called bicuculline

42
Q

what does orientation selectivity require

A

inhibition

43
Q

as orientation selectivity requires inhibition, what happens to orientation selectivity of area v1 cells when there is no inhibition i.e. the presence of bicuculline

A

the cell RF will respond to any orientation, even stimuli that are at 90 degrees (orthogonal) to the RF, e.g. a vertical RF responds to a horizontal stimulus

44
Q

what do hyper complex cells best respond to

A

a short oriented bar with with a size that is confined to its RF (dotted square)

45
Q

when is the response of a hyper complex cell reduced

A

when the length of the bar extends slightly beyond the left or right side of the RF and is completely inhibited when the bar is much longer

46
Q

what is it called when the length of the bar extends slightly beyond the left or right side of the RF and is completely inhibited when the bar is much longer of a hyper complex cell

A

end-stopping

47
Q

what does end-stopping of a hyper complex cell imply

A

that the cell’s RF posses a silent inhibitory surround

48
Q

what do spatial frequency selectivity of area v1 cells also involve

A

local inhibitory mechanisms

49
Q

why do spatial frequency selectivity of area v1 cells also involve local inhibitory mechanisms

A

individual LGN neurons respond to a wider range of spatial frequencies than area v1 orientation-selective cells i.e. are more tightly tuned

50
Q

what are the spatial frequency curves for their tunings much wider for

A

spatial frequency of neurons in the primary v1 cortex since the LGN supplies to v1

51
Q

when are the broad tuning curves reduced to a smaller tuning curve

A

by the presence of inhibition within layers of v1 cortex

52
Q

what are direction selective cells concentrated in

A

layer 4B

53
Q

which cell receptive fields have ON & OFF sub-zones

A

simple cells RFs

54
Q

what are inter blob cells tuned to

A

particular spatial frequencies

55
Q

what are the colour processing cells in CO blobs of area v1

A

wavelength selective

56
Q

what do many colour processing cells in CO blobs of area v1 have similarity with

A

centre-surround receptive fields similar to those of parvo-type ganglion cells & LGN neurons which code for red green contrast
or
like konio type ganglion cells & inter laminar LGN neurons which code for blue yellow contrasts

57
Q

what do motion processing layer 4B mainly contain

A

complex cells that are orientation & direction selective
i.e. they have rectilinear receptive fields & are preferentially activated by lines of a specific orientation, BUT only when the line is moving in one direction through their receptive field, with little or no response to the opposite non-preferred direction of motion of the same line stimulus

58
Q

what do the complex cells which are contained in the motion processing layer 4B respond very weakly to

A

stationary , flashed (would not like vertical bar flashed on & off in its RF), contours

59
Q

what do blob cells from 4Cb responds to

A

red/green colour

60
Q

what do inter blob cells from 4Ca and 4Cb respond to

A

form, contours

61
Q

what does layer 4B from 4Ca respond to

A

motion processing by complex cells in which are orientation & direction selective

62
Q

what do blob cells from the konio pathway respond to

A

blue/yellow colour (not the same blob cells which are interested in red/green colour)

63
Q

what is v1 conceived as comprising 1000’s of

A

adjacent hypercolumns

64
Q

what do each of the 1000’s of adjacent hypercolumns that v1 is conceived of represent

A

a single point in space via a left and right eye ocular dominance column across the entire hemi-field map in area v1
(so one single point in our field of view in the opposite hemi-field)

65
Q

what do each left and right ocular dominance columns of adjacent hyper columns in v1, further contains cells with

A
  • a full range of orientation & spatial frequency preferences in its inter blob zones
  • a full range possible direction-selective preferences in layer 4B (e.g. vertical lines moving in right or left direction, horizontal lines moving up or down, all information is in the hyper column)
  • plus two CO blobs; 1 for red/green & 1 for blue/yellow processing
66
Q

what is the functional significance of the hyper columns of v1 cortex

A
  • every possible visual stimulus - regardless of its form, motion or colour - is encoded by some cells in the hyper column (even if it can’t be seen by one eye)
  • so nothing is ‘invisible’ to cells in v1
67
Q

what do the hyper columns of v1 cortex have all possible..

A

stimulus orientations, spatial frequencies, directions & colours seen by either eye are represented for every point in the visual hemifield, which extend to the ocular dominance columns where both eyes have the complete set or orientation preferences

68
Q

which points in space have their own hyper column

A

every, from fovea to periphery

69
Q

what do layer 4B have cells with different…

A

direction preferences

70
Q

so what do each of the two ocular dominance columns have a complete set of

A
  • orientation columns
  • direction preferences
  • two CO blobs - 1 for red/green & 1 for blue/yellow

there isn’t a single stimulus in visual nature that there isn’t a cell of the hyper column that can’t be detected, so it doesn’t matter what stimulus is in out FOV, we have a hyper column which has all the equipment in region of space to tell you information on, and it doesn’t matter if can only see the object with one eye, as each eye of our ocular dominance columns has the complete set of the cells in order to be able to see things

71
Q

how does parallel processing continue beyond area v1

A

v1 cortex divides or subcontracts the labour of processing different types of information to specialised higher cortical areas involved in specific aspects of visual perception, via parallel pathways originating from the different functional cell types in its hyper columns, this does so in steps and the pathways initially pass through area v2

72
Q

what does area v2 surround

A

v1 in the occipital lobes of each cortical hemisphere

73
Q

what does area v2 contain its own of

A

its own semi-field map

74
Q

what does area v2 possess the same of in v1 but different of in v1

A

possesses the classic 6 cell layers
but
layer 4 has no subdivisions & no myelin ‘stria or gennari’ but does have another unique pattern of cytochrome oxidase columns of variable width & staining intensity

75
Q

what are the unique pattern of cytochrome oxidase columns of variable width & staining intensity in area v2 organised as

A
  • thick
  • thin
  • pale
    stripes with a periodicity of 1mm across the upper and lower regions of the entire area
76
Q

so what do the stripes in area v2 which are a pattern of CO columns that run vertically through all the layers extend as

A

slabs from the junction of v1, all the way through to v2 to its outer edges, so the stripes which are rich of CO staining are quite thick & some stripes are thin with smaller amounts of CO and the regions in-between which are pale striped.

77
Q

how wide are the thick, thin & pale stripes in area v2 across

A

1mm across

78
Q

so what does CO form in area v2 instead of inter blobs

A

stripes

79
Q

which orientation do alternating CO stripes which run across area v2 are in relation to v1

A

orthogonal to the border with area v1 at the area 17/18 border

80
Q

the parallel pathways for v1 blob cells which have axons that come out and connect to…

A

v2 thin stripe cells (colour/continuation of colour processing pathway)

81
Q

the parallel pathways for v1 layer 4B cells have axons that come out and connect to

A

v2 thick stripe cells (motion, direction of movement in their FOV)

82
Q

the parallel pathways for v1 inter blob cells have axons that come out & connect to

A

v2 pale stripe cells (form/orientation)

Visual Science (14 decks)

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