Lecture 9 - Convergence and Receptive Fields Flashcards

1
Q

receptive field

A

part of the retina that responds in someway to affect the firing rate of target neurons

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2
Q

receptive field is always on the…

A

RETINA!

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3
Q

Receptive field corresponds to

A

a region in space (ex the visual field)

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4
Q

if activity is changing then we should see this in neurons its converging on later

A

if something is downstream the receptive field is still the receptive field on the retina

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5
Q

If a receptor connects to an inhibitory neuron, can it still be part of the receptive field?

A

YES, it’s still sending a signal (even it’s inhibitory) that can affect the firing rate

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6
Q

it’s not “on” that means activity, instead it’s…

A

any change in state

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7
Q

Primary Visual Cortex - V1

A

signals give us feature detectors

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8
Q

Where do retinal signals go?

A

optic nerve (bundle of axons from the retina) travels to the LGN down the optic track to V1

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9
Q

optic nerve

A

Approximately 1 million
ganglion cells send axons out of
each retina. These axons form
the optic nerve

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10
Q

superior colliculus

A

important for focusing the eyes: multisensory (touch, hearing, sight) and helps you plan out where the eyes will go and your attention

10% of the axons from the retina end up here

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11
Q

LGN (lateral geniculate nucleus)

A

part of the thalamus

90% of the axons from the retina end up here

About 900,000 ganglion axons
go to each LGN

about 360,000 LGN axons (40%) go to visual cortex. So, some processing is taking place.

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12
Q

How are retinal signals organized

A

the different parts of the eye seem to be segregated: visual field can be broken up into the left and right visual fields

everything opticly in the left it’s gunna end up on the right side of BOTH retinas

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13
Q

information to left visual field goes to

A

the right side of both retinas and the right LGN

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14
Q

Spatially organized transmission:

A
Items in the left visual field go the 
right side of both retinas. 
• Signals from the right side of both retinas go to the right lateral 
geniculate nucleus (LGN).
• Right visual field goes to the left 
side of the retinas and left LGN.
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15
Q

how are retinal signals organized?

A

Each LGN receives signals from both eyes, but the signals from each eye are sent to different layers.

layers are segregating which eye the info came from !!

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16
Q

each (half) eye sends
signals to both LGNs, but the
information from each eye is

A

is kept segregated.

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17
Q

LGN is a relay nucleus

A

taking info from the retina and sends it along to V1 because of its orgnaization

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18
Q

retina and LGN organize activation by…

A

spatial maps of a particular kind, in close register with the retina (retinotopic map)

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19
Q

Retinotopic map

A

each place on the retina corresponds to a place on the LGN

keeps all the cells/activity retinotopically organized

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20
Q

To determine retinotopic maps, perform ….

A

single cell recordings

record from neurons with an electrode that penetrates the LGN obliquely

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21
Q

LGN regulates (processes) ….

signals are received from?

A

…neural information from the retina and cortex before passing it to the primary visual
cortex (V1).

  • Signals are received from the retina, the cortex, the brain stem, and the thalamus.

– Signals from the eyes (bottom-up data) are organized by visual field, receptor type, and type of environmental information (e.g. color, orientation,
motion, etc.).

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22
Q

what may be happening in the LGN?

A

when you’re getting top-down information (it’s a dalmnation) - background knowledge biasing certain neurons to fire more and inhibiting others

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23
Q

LGN as perceptual gatekeeper?

A

Perhaps some of the feedback from cortex amplifies signals (or inhibits competing neurons) to enhance certain
features in a noisy environment.

– Background knowledge may help select visual images based on what you expect to see.

– Note: this kind of feedback happens at
many levels in the brain.

24
Q

receptive fields in LGN

A

are center surround (same as in the retina)

25
Visual field information segregated by.... from retina to LGN
...hemisphere
26
Information from each eye kept separate... from retina to LGN
.... in LGN by layers.
27
Cell receptive fields (center surround) are similar in the... from retina to LGN
... retina and LGN
28
Spatial retinotopic maps are preserved in.... from retina to LGN
....LGN
29
Some selective processing occurs - LGN is not simply a... from retina to LGN
.... relay nucleus
30
Occipital Lobe
The optic radiation goes from the LGN to V1, primary visual cortex. • V1 has cells with the smallest receptive fields in the visual cortex. • Receptive fields get more complex from here. • Information across visual fields and eyes is now integrated for the first time in V1.
31
Hubel and Wiesel
demonstrated the firing properties of cells in the striate cortex (V1). • Using the single-cell recording method, they recorded cortical cells of anesthetized cats while presenting different stimuli. • Received the Nobel prize for physiology and medicine in 1982.
32
Electrodes that recorded activation from a cat’s visual cortex show:
• Receptive fields on the retina that are near one another are also near each other in the cortex!!!! • This pattern is seen using an oblique penetration of the cortex, as was done in LGN. !!!!Retinotopic maps retained in the visual cortex.!!!
33
cells in the cortex (V1) respond...
....differently than cells in the retina and LGN
34
simple cortical cells
come from center surround * Side-by-sidereceptive fields * Respond to spots of light • Respond best to bars of light oriented along the length of the receptive field
35
Orientation tuning curves
• Shows response of simple cortical cell for orientations of stimuli. • Cells respond best to particular orientations, and less well to others. helps to start characterizing the types of receptive fields in V1
36
How do you end up with bar cells?
– Simple cells are created by the convergence of LGN axons. – Points of light will activate the simple cell; however, it is best activated by the correctly oriented bar. – This is hierarchical processing –
37
hierarchical processing
representations are built from simple receptive field and become more complex as you go ‘higher’ in cortex.
38
complex cells
even more specific in their responses like bars of light in a particular location, but also like movement in a particular direction are made by the convergence of simple cells
39
End-Stopped Cells
more specific!!! bar, moving, AND A SPECIFIC LENGTH come from complex cells
40
hierarchy of cells
center surround -> simple cells -> complex cells -> end stopped cells
41
V1 Cells as feature detectors
• These neurons fire to specific features of a stimulus. [Think of these as object edge detectors.] • Neurons farther along in the visual pathway fire to more complex stimuli in a hierarchical manner. • Good to know for the exam.
42
Cells that are feature detectors:
– Simple cortical cell – Complex cortical cell – End-stopped cortical cell
43
fovea has greater representation in the.....
...striate cortex (V1) than | proportionally anticipated.
44
cortical | magnification factor
expanding the amount of cortex you're gunna use when it's functionally important to the organism – Fovea accounts for .01% of retina – Signals from fovea account for 8% to 10% of the visual cortex – This provides additional processing for high-acuity tasks.
45
LGN and top down processing
More signal comes from the cortex | than the eyes.
46
How are signlas in V1 organized? retinotopic maps?
Retinotopic maps retained in | the visual cortex.
47
simple cells are created by
the convergence of LGN axons
48
unlike simple cells, complex cells respond to _____ of bars of light in a specific direction
movement
49
How are complex cells activated?
– Simple cells were made by the convergence of LGN cells. – Complex cells are made by converging simple cells (probably).
50
End-stopped cells respond to
moving lines of specific lenghth moving corners or angles
51
end-stopped cells have no response to
stimuli that are too long stimuli moving in the wrong direction
52
how are end stopped cells formed?
made by converging signals from complex cells with striate cortex (V1)
53
cells that are feature detectors
– Simple cortical cell – Complex cortical cell – End-stopped cortical cell
54
feature detector neurons fire to...
.... specific features of a stimulus
55
neurons farther along in the visual pathway fire to more...
....complex stimuli in a hierarchical manner