Primary visual cortex: Binocular inputs Flashcards
what does the left field of the projection of the binocular visual field map
onto nasal retina of left eye
&
temporal retina of right eye
what does the right field of the projection of the binocular visual field map
to the nasal retina of right eye
&
temporal retina of left eye
what is the result of, nasal axons crossing at the chiasm and temporal axons not crossing at the chiasm
left hemi-field, right side of brain
right hemi-field, left side of brain
in the right LGN, which layers of the LGN do the nasal (crossed) retinal axons terminate
layers: 1, 4 & 6
in the right LGN, which layers of the LGN do the temporal (ipsilateral) retinal axons terminate
layers: 2, 3 & 5
what is the significance of nasal and temporal retinal axons terminating at a specific layer in the right LGN
one point in the binocular region of the left hemi-field projects to cells in each layer in the form of a vertical column
what does each layer (6) of the LGN contain maps of
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
where does the retinal input come from for layer 1 of the LGN
nasal of the contralateral eye
where does the retinal input come from for layer 2 of the LGN
temporal of the ipsilateral eye
where does the retinal input come from for layer 3 of the LGN
temporal of the ipsilateral eye
where does the retinal input come from for layer 4 of the LGN
nasal of the contralateral eye
where does the retinal input come from for layer 5 of the LGN
nasal of the ipsilateral eye
where does the retinal input come from for layer 6 of the LGN
nasal of the contralateral eye
what do the cells on the dotted vertical, line of binocular visual projection represent
the same position in space in the opposite hemi-field in both eyes
from where to where does the left and right eye maps of the opposite hemi-field go
fovea to macula to periphery, mapped across the nasal and temporal retina of each eye
where do the periphery parts of the left and right eye maps of the opposite hemi-field look
way into the periphery
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
related to the fovea (f)
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
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
what is right next to M
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
where does the segregation of left and right eye inputs continue in
the LGN pathway to the v1 cortex
what do the LGN neurons receiving input from each eye send inputs to area v1 form
alternating ‘ocular dominance’ bands in layer 4C, the same point is side by side, adjoining points in space are next door
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
sit side by side (horizontal) which leads to ocular dominance bands
so what are the left and right inputs from the same points in space onto
are onto adjoining cells in layer 4C of area v1 cortex
what do the connections with granule cells in layer 4C form
a little group of neurons which run through the internal capsule and optic radiations to layer 4C
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
- 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
explain how to extract evidence for segregated left & right eye inputs to the different layers of the LGN
- inject radioactive amino acid into left eye
- absorbed by ganglion cells & transported down their axons to the left & right LGN
- black - they layers in which their axons terminate in the ipsilateral (left) & contralateral (right) LGN
- white = layers receiving unlabelled right eye input
what is the evidence for segregated left and right eye inputs from the LGN to v1 cortex: ocular dominance bands in layer 4C
- neurons in LGN layers 1,4&6 take up the radioactive amino acid, and..
- transport it via their axons to layer 4C of the right primary v1 cortex, where…
- black = patches of their (LEFT EYE) input terminates in layer 4C, alternating with…
- 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
what does the lower bank of the calcarine sulcus represent
upper quadrant of visual space
what does the upper bank of the calcarine sulcus represent
lower quadrant of visual space
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
on adjoining patches of layer 4C cells
where do cortical inputs from LGN layers representing the adjoining (next-door) point in space in the left & right eyes terminate
on adjoining (next-door) cells in layer 4C
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
visual stimulation of that given eye = ocular dominance COLUMNS
where do layers of granule axons from layer 4C make connections
above and below called ocular dominance columns
list how David Hubel & Torsten Wiesel recorded activity of single v1 cells with a micro electrode and what they discovered
- 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
which cells only respond to stimuli presented to one eye alone
retinal ganglion cells
LGN neurons and
layer 4C cells
when are cells activated by both eyes
after layer 4C
how can the eyes respond to stimuli presented to either eye, i.e. binocularly
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
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
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
what happens when the 0.5mm electrode passes from one ocular dominance column to the next
ocular preference reverses systematically between left and right eye and so did the location in space that they were interested in
what type/shape RFs do cells beyond layer 4C have
square or rectangular RFs
what do the RFs beyond layer 4C respond to
lines and edges and other contours of a particular orientation
what type of RFs do RGCs, LGN neurons & layer 4C granule cells have
circular, centre-surround, antagonistic RF organisations
what do the RFs beyond layer 4C which are rectangular shaped preferentially activated or excited by (most action potentials)
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
orientation preferences vary within RFs beyond layer 4C, but what principle always remains the same
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
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
the same stimulus orientation preference
except in layer 4C where cells respond non-selectively to all orientations
out of the horizontal/tangential organisation of columns in area v1 cortex, how does the orientation preference of adjoining cells change
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
how are the cells organised so the cells look at different orientations in space
orientation preference is organised so theres a systematic change, horizontal to oblique to vertical
at which orientation do cells have orientation preferences which change systematically
horizontal/tangential
at which orientation do cells have the same orientation preferences
vertical
in which area are cells not orientation selective
layer 4C, they respond to all orientations of lines
in which area do cells have the same orientation preference
layers above and below 4C, same oblique line in the same region of space
what does the ice cube model show
how two columnar systems relate to each other
what is the result of the ice cubes looking at next door regions of space
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
in the ice cube model, what does each set of ocular dominance column have
a complete set of preferred columns = horizontal, oblique, vertical
in the primary visual pathway, what happens to the amount of axon fascicles between the optic nerve and chiasm
they decrease
in the primary visual pathway, what does each layer of the LGN receive retinal inputs from
only one eye or the other
in the primary visual pathway, where do parasol ganglion cell axons originating in the nasal retina terminate
in LGN layer 1
in the primary visual pathway, how many neurons in area v1 are binocularly activated
none in layer 4C some outside (above and below) layer 4C
