Primary visual cortex: Binocular inputs

Question 1

what does the left field of the projection of the binocular visual field map

Answer 1

onto nasal retina of left eye
&
temporal retina of right eye

Question 2

what does the right field of the projection of the binocular visual field map

Answer 2

to the nasal retina of right eye
&
temporal retina of left eye

Question 3

what is the result of, nasal axons crossing at the chiasm and temporal axons not crossing at the chiasm

Answer 3

left hemi-field, right side of brain

right hemi-field, left side of brain

Question 4

in the right LGN, which layers of the LGN do the nasal (crossed) retinal axons terminate

Answer 4

layers: 1, 4 & 6

Question 5

in the right LGN, which layers of the LGN do the temporal (ipsilateral) retinal axons terminate

Answer 5

layers: 2, 3 & 5

Question 6

what is the significance of nasal and temporal retinal axons terminating at a specific layer in the right LGN

Answer 6

one point in the binocular region of the left hemi-field projects to cells in each layer in the form of a vertical column

Question 7

what does each layer (6) of the LGN contain maps of

Answer 7

it own hemi-field map of one eye in register with those in the layers above & below and of the opposite side of the visual field

Question 8

where does the retinal input come from for layer 1 of the LGN

Answer 8

nasal of the contralateral eye

Question 9

where does the retinal input come from for layer 2 of the LGN

Answer 9

temporal of the ipsilateral eye

Question 10

where does the retinal input come from for layer 3 of the LGN

Answer 10

temporal of the ipsilateral eye

Question 11

where does the retinal input come from for layer 4 of the LGN

Answer 11

nasal of the contralateral eye

Question 12

where does the retinal input come from for layer 5 of the LGN

Answer 12

nasal of the ipsilateral eye

Question 13

where does the retinal input come from for layer 6 of the LGN

Answer 13

nasal of the contralateral eye

Question 14

what do the cells on the dotted vertical, line of binocular visual projection represent

Answer 14

the same position in space in the opposite hemi-field in both eyes

Question 15

from where to where does the left and right eye maps of the opposite hemi-field go

Answer 15

fovea to macula to periphery, mapped across the nasal and temporal retina of each eye

Question 16

where do the periphery parts of the left and right eye maps of the opposite hemi-field look

Answer 16

way into the periphery

Question 17

what are all the lines which sit on the line of projection related to, on the right and left maps of the opposite hemi-field

Answer 17

related to the fovea (f)

Question 18

what do all the cells of the lines which sit on the line of projection related to f on the right and left maps of the opposite hemi-field look at

Answer 18

the same region of space within the fovea of left and right eyes as we move across to M of the map of column of cells which form a binocular projection which look at the macula region of visual space in the left side, and if move across there is another column for more peripheral part of visual field

Question 19

what is right next to M

Answer 19

another column of cells receiving binocular inputs as its within map of the visual field, each of these layers with maps stacked on top of one another, make connections with layer 4C of the primary visual cortex, but they now sit side by side

Question 20

where does the segregation of left and right eye inputs continue in

Answer 20

the LGN pathway to the v1 cortex

Question 21

what do the LGN neurons receiving input from each eye send inputs to area v1 form

Answer 21

alternating ‘ocular dominance’ bands in layer 4C, the same point is side by side, adjoining points in space are next door

Question 22

instead of the binocular line of projection doesn’t sit on top of one another like in the LGN, how are they in layer 4C

Answer 22

sit side by side (horizontal) which leads to ocular dominance bands

Question 23

so what are the left and right inputs from the same points in space onto

Answer 23

are onto adjoining cells in layer 4C of area v1 cortex

Question 24

what do the connections with granule cells in layer 4C form

Answer 24

a little group of neurons which run through the internal capsule and optic radiations to layer 4C

Question 25

name the steps from the left and right inputs from the same points in space onto adjoining cells in layer 4C of area v1 cortex

Answer 25

• fovea to macula to periphery
• lines of projections in the LGN
• geniculo-cortical axons in the optic radiations
• lines of projection now represented across layer 4C

Question 26

explain how to extract evidence for segregated left & right eye inputs to the different layers of the LGN

Answer 26

1. inject radioactive amino acid into left eye
2. absorbed by ganglion cells & transported down their axons to the left & right LGN
3. black - they layers in which their axons terminate in the ipsilateral (left) & contralateral (right) LGN
4. white = layers receiving unlabelled right eye input

Question 27

what is the evidence for segregated left and right eye inputs from the LGN to v1 cortex: ocular dominance bands in layer 4C

Answer 27

1. neurons in LGN layers 1,4&6 take up the radioactive amino acid, and..
2. transport it via their axons to layer 4C of the right primary v1 cortex, where…
3. black = patches of their (LEFT EYE) input terminates in layer 4C, alternating with…
4. white spaces = where the unlabelled input from layers 2,3&5 of the LGN represented the RIGHT EYE terminate

so the pattern made in layer 4C has dark regions with white regions in-between

Question 28

what does the lower bank of the calcarine sulcus represent

Answer 28

upper quadrant of visual space

Question 29

what does the upper bank of the calcarine sulcus represent

Answer 29

lower quadrant of visual space

Question 30

where do cortical inputs from LGN layers representing the same point on space via the left (1,4&6) & right (2,3&5) eyes terminate

Answer 30

on adjoining patches of layer 4C cells

Question 31

where do cortical inputs from LGN layers representing the adjoining (next-door) point in space in the left & right eyes terminate

Answer 31

on adjoining (next-door) cells in layer 4C

Question 32

what are the cells in area v1 in the layers vertically above or below the patches of left or right eye input in layer 4C tend to be excited more by

Answer 32

visual stimulation of that given eye = ocular dominance COLUMNS

Question 33

where do layers of granule axons from layer 4C make connections

Answer 33

above and below called ocular dominance columns

Question 34

list how David Hubel & Torsten Wiesel recorded activity of single v1 cells with a micro electrode and what they discovered

Answer 34

• they plotted their RF positions to ‘preferred’ light stimulus on screen, with one eye open (e.g. left) & the other (e.g. right) covered, then rise versa
• they discovered that most v1 cells above & below layer 4C respond to the same stimulus in the same place in space through both eyes = BINOCULARLY ACTIVATED

Question 35

which cells only respond to stimuli presented to one eye alone

Answer 35

retinal ganglion cells
LGN neurons and
layer 4C cells

Question 36

when are cells activated by both eyes

Answer 36

after layer 4C

Question 37

how can the eyes respond to stimuli presented to either eye, i.e. binocularly

Answer 37

the the granule cells in the adjoining layer 4C left & right eye ocular dominance bands make convergent, excitatory synapses with pyramidal cells in layers above & below so that they can respond to stimuli presented to wither eye/binocularly

Question 38

what can a 0.5mm vertical electrode above and below a left eye ocular dominance band in layer 4C, receiving input from the left eye into layer 4C discover

Answer 38

that both the neurons in that column were activated by the left and right eyes in both regions of space, but with a slight preference to the stimulus presented to the left eye compared to the right eye (and vice versa for right eye ocular dominance bands), so inputs to these cells above layer 4C was dominated by the eye providing input into layer 4C

Question 39

what happens when the 0.5mm electrode passes from one ocular dominance column to the next

Answer 39

ocular preference reverses systematically between left and right eye and so did the location in space that they were interested in

Question 40

what type/shape RFs do cells beyond layer 4C have

Answer 40

square or rectangular RFs

Question 41

what do the RFs beyond layer 4C respond to

Answer 41

lines and edges and other contours of a particular orientation

Question 42

what type of RFs do RGCs, LGN neurons & layer 4C granule cells have

Answer 42

circular, centre-surround, antagonistic RF organisations

Question 43

what do the RFs beyond layer 4C which are rectangular shaped preferentially activated or excited by (most action potentials)

Answer 43

a line (black bar) oriented at 45 degrees, with no responses at all to ‘non-preferred’ vertical or horizontal orientations of the same line stimulus

Question 44

orientation preferences vary within RFs beyond layer 4C, but what principle always remains the same

Answer 44

all cells always hate it if the stimulus is at 90 degrees to their preference e.g. a cell preferentially activated or excited by a vertically-orientated line (black bar), with a smaller response to slightly off-vertical & no response at all to a non preferred horizontal orientation of the same line stimulus

Question 45

out of the orientation column in area v1 cortex, vertical columnar organisation, what do all the cells have and except in which area do they not follow this pattern

Answer 45

the same stimulus orientation preference

except in layer 4C where cells respond non-selectively to all orientations

Question 46

out of the horizontal/tangential organisation of columns in area v1 cortex, how does the orientation preference of adjoining cells change

Answer 46

changes systematically across the full range of possible stimulus orientations e.g. from vertical, through oblique, to horizontal & back to vertical again

and these orientations columns are aligned orthogonally (at 90 degrees) to the ocular dominance columns, so that cells with the full range of possible orientation preferences can be activated from the same regions of space through either the left or right eyes = the ice cube model

Question 47

how are the cells organised so the cells look at different orientations in space

Answer 47

orientation preference is organised so theres a systematic change, horizontal to oblique to vertical

Question 48

at which orientation do cells have orientation preferences which change systematically

Answer 48

horizontal/tangential

Question 49

at which orientation do cells have the same orientation preferences

Answer 49

vertical

Question 50

in which area are cells not orientation selective

Answer 50

layer 4C, they respond to all orientations of lines

Question 51

in which area do cells have the same orientation preference

Answer 51

layers above and below 4C, same oblique line in the same region of space

Question 52

what does the ice cube model show

Answer 52

how two columnar systems relate to each other

Question 53

what is the result of the ice cubes looking at next door regions of space

Answer 53

for every position in space, you have an ice cube in v1 cortex, that has input for left and right eyes and has a complete set of orientation column

Question 54

in the ice cube model, what does each set of ocular dominance column have

Answer 54

a complete set of preferred columns = horizontal, oblique, vertical

Question 55

in the primary visual pathway, what happens to the amount of axon fascicles between the optic nerve and chiasm

Answer 55

they decrease

Question 56

in the primary visual pathway, what does each layer of the LGN receive retinal inputs from

Answer 56

only one eye or the other

Question 57

in the primary visual pathway, where do parasol ganglion cell axons originating in the nasal retina terminate

Answer 57

in LGN layer 1

Question 58

in the primary visual pathway, how many neurons in area v1 are binocularly activated

Answer 58

none in layer 4C
some outside (above and below) layer 4C