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neuro 80 > lecture 15 vision central pathways > Flashcards

lecture 15 vision central pathways Flashcards

1
Q

output of thalamus

A

primary visual cortex aka striate cortex, or v1, or area 17

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2
Q

primary visual cortex

A

located in occipital cortex

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3
Q

retinopy

A

2d surface of retina mapped onto 2d surface of thalamus and cortex

l and r visual fields seamlessly knit together despite being in very different parts of the brain

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4
Q

why are the central few degrees of the visual field over-represented (magnified)

A

for better acuity in the center of the visual field

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4
Q

why are the central few degrees of the visual field over-represented (magnified)

A

for better acuity in the center of the visual field

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5
Q

cortical lamination

A

cortex is also layered into 1-6
but layer 4 is broken into abc and c broken into alpha and beta
after layer 6 is white matter (myelinated axons)

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6
Q

neocortex

A

6-9 layers in gray matter

division of function as in lgn with different organization

much of thalamic input goes to layer 4

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7
Q

cortical neurons

A

excitatory release glutamate
inhibitory release gaba

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8
Q

ocular dominance columns in v1

A
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9
Q

radioactive protein injected into eye

A

radioactive lgn terminals labeled by transsynaptic transport of radioactive proline containing protein injected into only one retina (white stripes)

*mainly evident in layer 4

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10
Q

hubel and wiesel

A

extended kuffler’s rgc receptive field mapping first to lgn and then to v1

developed an extracellular electrode that picked up action potential activity of neurons in the vicinity of the electrode while animals looked at things

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11
Q

layer 4 neurons

A

have receptive fields like rgcs
monocular
center surround

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12
Q

outside layer 4

A
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13
Q

receptive field properties outside IVC

A

binocular: v1 cortical neurons respond to both eyes

orientation selectivity of the receptive field in an organized pattern

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14
Q

what kind of circuit could generate orientation specificity

A

parts of the pathway closer to the retina are all on or off center with antagonistic surround

maybe convergence of several center surround cells that form a line is the basis of the orientation specificity

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15
Q

how would cortical neurons work together to help us see a triangle

A
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16
Q

binocular stereopsis (depth perception)

A

neurons found in v1 (cat) and v2 (monkey and humans) that selectively respond to lateral disparity in r and l visual fields

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17
Q

a receptive field property in upper and lower layers

A

requires binocular aligned vision

devices that simulate stereopsis by viewing two pictures (one in each eye) of the same scene from slightly different angles

based on horizontal disparity in the position of the left and right receptive fields of binocular cortical neurons

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18
Q

depth perception

A

brain interprets depth by objects deviated laterally being close to you and objected deviated medially being far from you

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19
Q

Visual field

A

portion of the external world that can be seen at a given time

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20
Q

Ipsilateral

A

pertaining to the same side of the body

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21
Q

Contralateral

A

pertaining to the opposite side of the body

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22
Q

Temporal retina

A

Half of the retina closest to the temple, receives visual information from the contralateral visual field and fibers project to the ipsilateral LGN

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23
Q

Nasal retina

A

Half of the retina closest
to the nose, receives visual information from the ipsilateral visual field and fibers
project to the contralateral LGN

24
Q

Optic nerve

A

bundle of retinal ganglion
axons that sends visual information from the eye to the brain before the optic chiasm. Each nerve contains axons from 1 eye, both visual field

25
Q

Optic chiasm

A

structure in the midline
where the axons from the nasal retina cross to the contralateral side

26
Q

Optic tract

A

bundle of retinal ganglion
axons after the optic chiasm. Each
nerve contains axons from both eyes, just 1 visual field, contralateral to the tract

27
Q

Lateral geniculate nucleus (LGN)

A

nucleus in the thalamus that receives visual input from
retinal ganglion cell axon and sends output to the primary visual cortex. The LGN as a whole
receives visual information from both eyes, but individual layers (6 layers in primates) including
individual neurons, receive synaptic connections from just one eye

28
Q

magnocellular

A

In primates, the most ventral layers (#1 and 2) are known as the magnocellular layers. Layer 1
receives input from the contralateral M-type RGCs and layer 2 receives input from the ipsilateral M-type RGCs

29
Q

parvocellular

A

Layers 3 through 6 are the parvocellular layers. Layers 4 and 6 receive input from the contralateral P-type RGCs and layers 3 and 5 receive input from the ipsilateral
P-type RGCs. Between the lays are numerous, tiny neurons known as koniocelluar cells that
are critical for processing color

30
Q

Optic radiation

A

axons from the LGN that carry visual information to the cortex

31
Q

Primary visual cortex (V1)/Striate cortex

A

the cortical area that receives direct input from the
LGN. The cortex is a layered structure and cells in layer 4 receive direct connections from the
LGN. Layer 4 neurons typically make synapses onto layer 2/3 neurons, which make
connections to layer 5/6 neurons and other locations in the brain. The term striate refers to the
fact that area V1 has an unusually dense stripe of myelinated axons run-in parallel to the
surface that appears white in installed sections

32
Q

Extrastriate cortex

A

areas of cortex beyond V1 that receive and respond to visual information. Receptive fields tend to change in extrastriate areas, generally retinotopy persists, but
receptive field covers a larger area of the visual field and may also respond to other visual
information (e.g. movement or shape

32
Q

Simple cell

A

descriptive term for a neuron in V1 with a receptive field shaped not like the simple center/surround
found in the retina (and LGN) but rather an elongated field
with a specific orientation

33
Q

neuronal tuning is the idea that neurons can
respond dynamically (usually firing rate) to different stimuli.
If a neuron is tuned to a particular aspect of a stimulus,
that neuron will have a greater response to the preferred
stimulus and weaker or no response to non-preferred
stimuli

A

tuning

34
Q

Orientation tuning

A

simple cells in the visual system are tuned for orientation, or edge (line)
direction

35
Q

Monocular

A

in this instance, monocular refers to neurons that are only responsive to one eye (either R or L). Neurons in the retina, LGN, and layer 4 of V1 are all monocular

36
Q

Binocular

A

in this instance, monocular refers to neurons that are only responsive stimulation of either eye. A neuron might be mored turned to either R or L, and respond weakly to stimulation of the non-tuned eye, or a neuron might respond to both eyes equally. Ocular dominance is the term used to describe the preference a neuron has for
one eye or another. Binocular neurons are found after
layer 4 in the visual system

37
Q

Columnar organization

A

Neurons within a column of
V1 (from layer 2/3 down to layer 6) have the same
tuning (e.g. same orientation selectivity), and there is an
orderly shift in orientation across a small area of V1.
Additionally, there are alternating columns of L or R
ocular dominance. Although typically drawn as a grid,
the columns are not particularly parallel or straight

38
Q

Parallel processing

A

the idea that different stimulus
attributes are process by the brain in parallel using distinct (parallel) pathways

Beyond the primary visual cortex (V1), the receptive field properties become increasingly more
complex. There are two major processing pathways out of primary visual cortex: the ventral
and dorsal streams

39
Q

Dorsal stream

A

visual processing pathway from
primary visual cortex to the parietal cortex. It is responsible for analyzing motion and depth. The
“where” stream.

40
Q

Ventral stream

A

visual processing pathway
from primary visual cortex to the temporal cortex. It is responsible for analyzing form and color. The “what” stream

41
Q

Understand visual fields. Explain how they are projected on to the retina, and how they
propagate through the LGN and then to cortex

A
42
Q

describe the anatomy of the visual thalamus (LGN)

A
43
Q

Describe the columnar organization and retinotopic (topographic) organization of visual
cortex

A
44
Q

Compare the receptive fields of neurons in layer IV of visual cortex to both cells in the LGN/
RGCs and the other layers in V1

A
45
Q

Illustrate and explain how information from both eyes combine to create binocular vision

A
46
Q

Cells that are inhibited by light in their center are excited by light in their surround. True or false

A

True

47
Q

Which of the following statements about center-surround receptive fields in the retina is false?

The best stimulus for an on-center cell is light in its center and darkness in its surround.

The surround portion of the receptive field is typically an annulus (or donut-shaped ring) that surrounds the circular center.

The spatial extent to which a cell can be influenced by light never extends beyond the physical extent of its dendritic field.

A

The spatial extent to which a cell can be influenced by light never extends beyond the physical extent of its dendritic field.

48
Q

Which of the following represents the most direct pathway for the transmission of visual information from the eye to the brain?

Photoreceptor->-horizontal cell–>ganglion cell–>brain

Horizontal cell–>bipolar cell–>ganglion cell–>brain

Photoreceptor–>bipolar cell–>amacrine cell–>brain

Photoreceptor–>bipolar cell–>ganglion cell–>brain

A

Photoreceptor–>bipolar cell–>ganglion cell–>brain

49
Q

In humans, at the optic chiasm _____

axons from each temporal retina decussate

axons from each nasal retina decussate

all axons leaving the eye cross over to the contralateral side

all axons from both eyes converge and then randomly segregate to each hemisphere

A

axons from each nasal retina decussate

50
Q

Ocular dominance columns in layer IV of V1 segregate input by _____.

on vs off receptive fields
different eyes
different colors
different visual hemi-fields

A

different eyes

51
Q

The parvocellular and magnocellular layers of the lateral geniculate nucleus…

receive input from the contralateral and ipsilateral halves of the visual field, respectively.

analyze the same kind of information from the visual field.

are connected to the nasal and temporal halves of the retina, respectively.

may belong to different parallel pathways.

A

may belong to different parallel pathways.

52
Q

person with damage to the ventral stream will have the most trouble with which task?

Recognizing a familiar face

Analyzing the speed of a moving target

Following the movement of a stimulus

Determining distances between objects

A

Recognizing a familiar face

53
Q

person with damage to the ventral stream will have the most trouble with which task?

Recognizing a familiar face

Analyzing the speed of a moving target

Following the movement of a stimulus

Determining distances between objects

A

Recognizing a familiar face

54
Q

Following a bicycle accident, you are disturbed to find that you cannot see anything in your left visual field. Where has the retinofugal pathway been damaged?

A

The accident has resulted in a transection of the right optic tract, resulting in blindness in the left visual field as viewed through either eye. Axons form the nasal retina of the left eye and temporal retinal of the right eye have been damaged. In contrast, a transection of the right optic nerve would render a person blind in the right eye because both nasal and temporal axons originating form the right eye would be damaged; none of the axons in the optic nerve have crossed to the opposite side of the brain. Crossing or decussation, occurs at the optic chiasm, which lies between the optic nerve and the optic tract.

55
Q

What is the source of most of the input to the left LGN?

A

receives retinal info about the right visual fields. Left LGN neurons receive synaptic input form the retinal ganglion cells in the nasal half of the right retina and the temporal half of the left retina. In the left LGN, the left eye (ipsilateral) axons synapse on cells in layers 2,3, and 5 and the right (contralateral) eye axons synapse on the cells in layers 1, 4, and 6.

56
Q

A worm has eaten part of one lateral geniculate nucleus. You cannot longer perceive motion in the right visual field off your right eye.

A

The worm has eaten magnocellular neurons in the right LGN, which corresponds to layer2. the right visual field of your right eye corresponds to the temporal retina. This info does not cross at the optic chiasm, so will project to the ipsilateral (right in this case) LGN. Motion is processed by magnocellular neurons (getting info from retinal M-cells). The magnocellular layers of LGN are the two most ventral layers, with layer 2 receiving info from the ipsilateral retina.

neuro 80 (25 decks)

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