the visual cortex Flashcards
where are signals from each visual field relayed to?
eye and input specific areas of the LGN
which layer has the most sub-lamination in the visual cortex
layer 4
structure of the visual cortex
6 layer structure with some sub-lamination
what does golgi staining of V1 show?
all of some cells
how can cells in the cortex be classified?
based on morphology of cell body
based on distribution of dendrites or axon terminations
features of cells in te cortex
ubiqutous
there is a common organising plan
pyramidal cell
- ‘spiny’ dendrites seen at higher magnification
- Increases the surface area for synaptic contact
- Allow for local ‘computation’
determining location and properties
- Record electrophysiologically to define sensory properties
- Fill with dye to determine morphology
- Counterstain (e.g. nissl) to find laminar position
spiny cells
- > 80% of cortical cells
- Glutamatergic
non spiny cells
- <20% of cortical cells
- GABAergic
excitatory cortex cells
pyramidal (2/3, 5, 6)
stellate (4)
spiny
glutamatergic
distant and local targets
inhibitory cortex cells
stellate
fusiform
Bi-tufted etc.
aspiny (smooth)
GABAergic (peptides)
local targets
cortex layer 1
cells sparse
dendrites and axons
cortex layer 2
external granule layer
mainly small pyramidal cells
cortical layer 3
variety of cell types
many pyramidal: deeper in the layer
the external pyramidal layer
cortex layer 4
primary spherical cells
granule cell layer
cortex layer 5
cells typically layer than layer III
internal pyramidal
cortex layer 6
heterogeneous mix
polymorphic or multiform layer
supragranular cortex layers
layer 1, 2 ,3
infragranular cortex layers
layers 5, 6
parvocellular local circuit
LGN
projects to 4Cbeta
projects to 2/3
projects back to 5
projects back to 6
projects back to 4Cbeta
magnocellular local circuit
LGN
projects to 4Calpha and 6
projects to 4B
projects to 2/3
projects back to 5
projects back to 6
projects back to 4Calpha
koniocellular local circuit
LGN projects to layer 2/3 and projects to layer 6
general local circuit
LGN
projects to 4
projects to 2/3
projects back to 5
projects back to 6
projects back to 4
what signals are fed back to layer 4
modified versions of the original input signals
where do sensory properties change in local circuit?
from LGN to layer 4
from layer 4 to layer 2/3
output of koniocellular circuit
layer 2/3 to V2
layer 6 to LGN
output of magnocellular circuit
layer 2/3 to V2
layer 4B to area V5 (MT)
layer 5 to SC an Pulvinar
layer 6 to LGN
parvocellular output circuit
layer 2/3 to V2
layer 5 to SC and Pulvinar
layer 6 to LGN
LGN output signal
modulate input
output to V5 (MT)
motion processing
output to SC and pulvinar
eye movements, attention
what area has the greatest magnification in V1?
fovea
is magnification of fovea larger in V1 or LGN?
V1
where does binocular convergence begin?
layer 2/3
where are LGN inputs segregated?
layer 2/3
eye-specific LGN layers project to separate zones in the cortex: ocular dominance columns
what type of organisation do the cells that V1 receives its input from have?
ON and OFF centre surround circular receptive fields
V1 simple cells
- Separate ON and OFF sub regions
- Elongated receptive fields
- Wide variety of orientations and arrangements
- Layer 4
- Convergent input
multiple LGN cells to one simple cell - Respond to specific polarity of light and dark with specific orientations
what cells does layer 4 contain?
simple cells
V1 complex cells
- Layer 2/3
- Convergent input
multiple simple cells
-similar orientation
-different subunit arrangement - Complex cells have overlapping ON and OFF subregions
- Respond to ‘any’ edges with correct orientation
what cells does layer 2/3 have?
complex cells
what cells does layer 6 have?
simple cells
what cells does layer 5 have?
complex cells
what doe hypercomplex cells respond to?
only to bars/edges of a specific length
hypercomplex cells
- A subset of both simple and complex cells showing ‘length tuning’
also known as end-stopped cells
useful for detecting corners/ curved edges
what is the effect of V1 orientation tuning?
stimulus responds stronger to a specific orientation
the ice cube model of orientation and ocular dominance
Hubel and Wiesel
for any point in space there should be a set of orientation columns for each eye
intercolumn connectivity
like-like connectivity
lateral communication between cells with the same preference
use of like-like connectivity
warn neighbours about moving stimuli etc
what are blob regions? where are they found?
cytochrome oxidase (CO) blobs in layer 2/3
regions have hive higher enzymatic activity in parts of layer 2/3
regularly spaced across the cortical surface
what are cell blobs selective for? what are they poorly tuned for?
selective for wavelength (colour tuned)
poorly tuned for orientation
what are interblobs tuned for?
orientation
cortical modules
- For every point in space there is a cortical module in V1
- One set of orientation columns in one pair of ocular dominance columns, with associated blobs
V1 cortical modules
V1 cortical modules:
For any point in space we have L and R ‘hypercolumns’ with-
A central region that processes colour
A set on orientation columns that pinwheel out from the centre
