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sensory systems > the visual cortex > Flashcards

the visual cortex Flashcards

1
Q

where are signals from each visual field relayed to?

A

eye and input specific areas of the LGN

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2
Q

which layer has the most sub-lamination in the visual cortex

A

layer 4

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3
Q

structure of the visual cortex

A

6 layer structure with some sub-lamination

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4
Q

what does golgi staining of V1 show?

A

all of some cells

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5
Q

how can cells in the cortex be classified?

A

based on morphology of cell body
based on distribution of dendrites or axon terminations

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6
Q

features of cells in te cortex

A

ubiqutous
there is a common organising plan

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7
Q

pyramidal cell

A
  • ‘spiny’ dendrites seen at higher magnification
  • Increases the surface area for synaptic contact
  • Allow for local ‘computation’
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8
Q

determining location and properties

A
  • Record electrophysiologically to define sensory properties
  • Fill with dye to determine morphology
  • Counterstain (e.g. nissl) to find laminar position
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9
Q

spiny cells

A
  • > 80% of cortical cells
  • Glutamatergic
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10
Q

non spiny cells

A
  • <20% of cortical cells
  • GABAergic
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11
Q

excitatory cortex cells

A

pyramidal (2/3, 5, 6)
stellate (4)
spiny
glutamatergic
distant and local targets

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12
Q

inhibitory cortex cells

A

stellate
fusiform
Bi-tufted etc.
aspiny (smooth)
GABAergic (peptides)
local targets

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13
Q

cortex layer 1

A

cells sparse
dendrites and axons

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14
Q

cortex layer 2

A

external granule layer
mainly small pyramidal cells

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15
Q

cortical layer 3

A

variety of cell types
many pyramidal: deeper in the layer
the external pyramidal layer

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16
Q

cortex layer 4

A

primary spherical cells
granule cell layer

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17
Q

cortex layer 5

A

cells typically layer than layer III
internal pyramidal

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18
Q

cortex layer 6

A

heterogeneous mix
polymorphic or multiform layer

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19
Q

supragranular cortex layers

A

layer 1, 2 ,3

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20
Q

infragranular cortex layers

A

layers 5, 6

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21
Q

parvocellular local circuit

A

LGN
projects to 4Cbeta
projects to 2/3
projects back to 5
projects back to 6
projects back to 4Cbeta

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22
Q

magnocellular local circuit

A

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

23
Q

koniocellular local circuit

A

LGN projects to layer 2/3 and projects to layer 6

24
Q

general local circuit

A

LGN
projects to 4
projects to 2/3
projects back to 5
projects back to 6
projects back to 4

25
Q

what signals are fed back to layer 4

A

modified versions of the original input signals

26
Q

where do sensory properties change in local circuit?

A

from LGN to layer 4
from layer 4 to layer 2/3

27
Q

output of koniocellular circuit

A

layer 2/3 to V2
layer 6 to LGN

28
Q

output of magnocellular circuit

A

layer 2/3 to V2
layer 4B to area V5 (MT)
layer 5 to SC an Pulvinar
layer 6 to LGN

29
Q

parvocellular output circuit

A

layer 2/3 to V2
layer 5 to SC and Pulvinar
layer 6 to LGN

30
Q

LGN output signal

A

modulate input

31
Q

output to V5 (MT)

A

motion processing

32
Q

output to SC and pulvinar

A

eye movements, attention

33
Q

what area has the greatest magnification in V1?

A

fovea

34
Q

is magnification of fovea larger in V1 or LGN?

A

V1

35
Q

where does binocular convergence begin?

A

layer 2/3

36
Q

where are LGN inputs segregated?

A

layer 2/3
eye-specific LGN layers project to separate zones in the cortex: ocular dominance columns

37
Q

what type of organisation do the cells that V1 receives its input from have?

A

ON and OFF centre surround circular receptive fields

38
Q

V1 simple cells

A
  • 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
39
Q

what cells does layer 4 contain?

A

simple cells

40
Q

V1 complex cells

A
  • 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
41
Q

what cells does layer 2/3 have?

A

complex cells

42
Q

what cells does layer 6 have?

A

simple cells

43
Q

what cells does layer 5 have?

A

complex cells

44
Q

what doe hypercomplex cells respond to?

A

only to bars/edges of a specific length

45
Q

hypercomplex cells

A
  • A subset of both simple and complex cells showing ‘length tuning’
    also known as end-stopped cells
    useful for detecting corners/ curved edges
46
Q

what is the effect of V1 orientation tuning?

A

stimulus responds stronger to a specific orientation

47
Q

the ice cube model of orientation and ocular dominance

A

Hubel and Wiesel
for any point in space there should be a set of orientation columns for each eye

48
Q

intercolumn connectivity
like-like connectivity

A

lateral communication between cells with the same preference

49
Q

use of like-like connectivity

A

warn neighbours about moving stimuli etc

50
Q

what are blob regions? where are they found?

A

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

51
Q

what are cell blobs selective for? what are they poorly tuned for?

A

selective for wavelength (colour tuned)
poorly tuned for orientation

52
Q

what are interblobs tuned for?

A

orientation

53
Q

cortical modules

A
  • 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
54
Q

V1 cortical modules

A

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

sensory systems (17 decks)

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