Primary visual cortex: columnar systems Flashcards
what are the names of the upper and lower part of layer 4C
upper = 4c alpha lower = 4c beta
what do the cells of layer 4c beta go on to
- blob cells
- inter blob cells
what do the cells of layer 4c alpa go on to
- inter blob cells
- layer 4B
what do the cells from the konio pathway go on to
goes straight to blob cells (doesn’t go to layer 4C)
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
in a small region of the primary visual cortex with dimensions of 1mmx1mm
where do left and right eye ocular dominance columns go to
layer 4c
what type of connections do layer 4c cells have
prominent vertical connections with the neurons above and below getting input from the right and left eye, predominantly from these ocular dominance columns
what type of selectivity do the neurons in the ocular dominance columns have
orientation selectivity which respond preferentially to lines, contours, edges of a particular orientation within their RFs
what do cells rich in cytochrome oxidase form
polka dot blob pattern
what do primate ocular dominance column run up and down
the primary v1 cortex
what do we have pillar/columns of
cytochrome oxidase rich cells, with regions next to the cells which also have cytochrome oxidase, but not as much of it
what type of RFs of inter-blob cells have and what do they respond to
rectilinear RFs
which respond preferentially (maximally) to slits, lines, bars or edges = contours of a particular orientation
what do RFs of inter-blob cells not respond to
to all non-preferred (especially orthogonal) orientation of the same stimulus
what preference do vertical columns of inter-blob cells have
the same orientation preference
what preference do horizontally/across columns of inter-blob cells have
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
list the three sub-types of orientation selective cells in these ocular dominance & orientation columns
- simple cells
- complex cells
- hypercomplex cells
how many % are there of simple cells
15%
how many % are there of complex cells
75%
how many % are there of hypercomplex cells
10%
which sub-type of orientation selective cells in these ocular dominance & orientation columns are most similar to ganglion and LGN cells
simple cells
which sub-type of orientation selective cells in these ocular dominance & orientation columns are least similar to the ganglion and LGN cells
complex cells
what type of sub regions do the simple cells have
spatially distinct
antagonistic
ON (excitatory) & OFF (inhibitory) sub-regions
as simple cells have ON (excitatory) & OFF (inhibitory) sub-regions, what shape are their RFs
Rsf are NOT circular, but are square or recti linear
what type of response do simple cells have with spots of light
weak
what type of response do simple cells have with stationary contours
strong
what type of summation and responses do simple cells have and why
linear summation
predictable responses, due to the sub-regions and due to amount of light falling onto the ON&OFF sub zone
why are their only a small minority of orientation selective cells have these types of RFs i.e. (15%) of simple cells
because their RFs resemble ganglion cells & neurons of the LGN
what type of RFs do complex cells have
larger RFs than simple cells with no spatially distinct ON or OFF sub-regions
what response do complex cells have to spots of light
none
what type of responses do complex cells have to stationary contours
weak
what type of responses do complex cells have to moving contours
better response than stationary contours
what type of responses do complex cells have and why
non-linear (unpredictable) responses, due to absence of sub-regions
how are complex cells responses non-linear and unpredictable
if the amount of light increases, response does not linearly correspond
what type of of RF organisation do hyper complex sub-type cells have
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
what are hyper complex cells RFs influenced by
stimulus size, length as well as contrast & orientation
what do all three sub-classes/types of orientation selective cells in the ocular dominance & orientation columns show
spatial frequency selectivity to grating stimuli i.e. some like low and some like high spatial frequency tuning
how many types of range of different types of contour & form do simple cells particularly like
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
how are these four types of RFs of simple cells constructed in v1
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
what reduces/loses the orientation selectivity of area v1 cells
blocking inhibition by the presence of GABA-receptor blocker
what happens when the GABA-blocker is removed
recovery
what is the antagonist of GABA receptors
a drug called bicuculline
what does orientation selectivity require
inhibition
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
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
what do hyper complex cells best respond to
a short oriented bar with with a size that is confined to its RF (dotted square)
when is the response of a hyper complex cell reduced
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
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
end-stopping
what does end-stopping of a hyper complex cell imply
that the cell’s RF posses a silent inhibitory surround
what do spatial frequency selectivity of area v1 cells also involve
local inhibitory mechanisms
why do spatial frequency selectivity of area v1 cells also involve local inhibitory mechanisms
individual LGN neurons respond to a wider range of spatial frequencies than area v1 orientation-selective cells i.e. are more tightly tuned
what are the spatial frequency curves for their tunings much wider for
spatial frequency of neurons in the primary v1 cortex since the LGN supplies to v1
when are the broad tuning curves reduced to a smaller tuning curve
by the presence of inhibition within layers of v1 cortex
what are direction selective cells concentrated in
layer 4B
which cell receptive fields have ON & OFF sub-zones
simple cells RFs
what are inter blob cells tuned to
particular spatial frequencies
what are the colour processing cells in CO blobs of area v1
wavelength selective
what do many colour processing cells in CO blobs of area v1 have similarity with
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
what do motion processing layer 4B mainly contain
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
what do the complex cells which are contained in the motion processing layer 4B respond very weakly to
stationary , flashed (would not like vertical bar flashed on & off in its RF), contours
what do blob cells from 4Cb responds to
red/green colour
what do inter blob cells from 4Ca and 4Cb respond to
form, contours
what does layer 4B from 4Ca respond to
motion processing by complex cells in which are orientation & direction selective
what do blob cells from the konio pathway respond to
blue/yellow colour (not the same blob cells which are interested in red/green colour)
what is v1 conceived as comprising 1000’s of
adjacent hypercolumns
what do each of the 1000’s of adjacent hypercolumns that v1 is conceived of represent
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)
what do each left and right ocular dominance columns of adjacent hyper columns in v1, further contains cells with
- 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
what is the functional significance of the hyper columns of v1 cortex
- 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
what do the hyper columns of v1 cortex have all possible..
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
which points in space have their own hyper column
every, from fovea to periphery
what do layer 4B have cells with different…
direction preferences
so what do each of the two ocular dominance columns have a complete set of
- 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
how does parallel processing continue beyond area v1
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
what does area v2 surround
v1 in the occipital lobes of each cortical hemisphere
what does area v2 contain its own of
its own semi-field map
what does area v2 possess the same of in v1 but different of in v1
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
what are the unique pattern of cytochrome oxidase columns of variable width & staining intensity in area v2 organised as
- thick
- thin
- pale
stripes with a periodicity of 1mm across the upper and lower regions of the entire area
so what do the stripes in area v2 which are a pattern of CO columns that run vertically through all the layers extend as
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.
how wide are the thick, thin & pale stripes in area v2 across
1mm across
so what does CO form in area v2 instead of inter blobs
stripes
which orientation do alternating CO stripes which run across area v2 are in relation to v1
orthogonal to the border with area v1 at the area 17/18 border
the parallel pathways for v1 blob cells which have axons that come out and connect to…
v2 thin stripe cells (colour/continuation of colour processing pathway)
the parallel pathways for v1 layer 4B cells have axons that come out and connect to
v2 thick stripe cells (motion, direction of movement in their FOV)
the parallel pathways for v1 inter blob cells have axons that come out & connect to
v2 pale stripe cells (form/orientation)
