Lecture 4: Parallel Processing

Question 1

1. Midget cells to what layer of LGN?
2. Parasol to what layer?
3. Bistratified to what layer?

Answer 1

1. Parvocellular (Dorsal 4 layers)
2. Magnocellular (Ventral 2 layers)
3. Interlaminar Regions

Question 2

1. Parvo are sensitive to what?
2. Magno?
3. Konio respond best to what?

Answer 2

1. Red-Green color contrast; No fast movement
2. Monochromatic, and respond to FAST MOVEMENT
3. respond well to Blue-Yellow Chromatic Contrast

Question 3

1. Parallel Processing: Define

Answer 3

1. Specific parts of Visual Info are Processed along specialized Visual Pathways (channels)

Question 4

X and Y Cells

• Came up during the study of cat ganglion cells
  1. What did X-Cells refer to?
  2. Y-cells?

Answer 4

1. Linear Cells
2. Non-linear cells
   * This was first studied in 1966.

Question 5

X-Cell

1. A Spatial Grating can be positioned w/in the Cell’s receptive field so that what happens?
   a. What is this position referred to?
   b. Why is it called this?

Answer 5

1. so that NO response is elicited.
   a. The NULL POSITION
   b. Because here, Excitation and INhibition are LINEARLY SUMMED and CANCEL each other. So, Excitation is equal to Inhibition.

Question 6

Y-Cell: nonlinear

1. Can a null position be found?
   a. What does this indicate?

Answer 6

1. No. There is always a response from the cell
   a. Cell doesn’t sum spatial info in a linear fashion. tells us X and Y cells play different roles in vision. (Parallel visual pathways)

Question 7

Photoreceptors

1. When exposed to light what do they do?
   a. This is related to what?

Answer 7

1. Hyperpolarize

a. Intensity of the stimulus

Question 8

Horizontal Cells

1. 2 Classes of Horizontal cells

Answer 8

1. H1 and H2

Question 9

Horizontal:

1. H1 Receive input from what?
2. H2 from where?

Answer 9

1. Primarily from M and L cones; Little input from S cones

2. Strong S-Cone input and input from L and M cones

Question 10

Horizontal

1. What do they sum up?
   a. High degree of spatial summation, what happens?

Answer 10

1. Input from Photoreceptors distributed over a LARGE AREA of the RETINA
   a. due to this HIGH level of SPATIAL SUMMATION, an ANNULUS Elicits a STRONG response from a HORIZONTAL CELL, causing it to Hyperpolarize

Question 11

Bipolar

1. On-Center bipolar Cells characterized by what?

Answer 11

1. By an INVAGINATING Synapse that they make w/Photoreceptors in the OPL

Question 12

Bipolar

1. Both on and off center bipolar cells synapse with what?
2. In Dark conditions, photoreceptors continuously release what?
   a. Light stimulation will do what?
3. For on Center Bipolar Cells: What molecule is inhibitory?
   a. A Reduction in its release causes what?

Answer 12

1. in the IPL
2. Neurotransmitter
   a. Causes Hyperpolarization of the Photoreceptors and a reduction of the neurotransmitter release
3. Glutamate
   a. Causes DEPOLARIZATION of the Bipolar Cell

Question 13

Bipolar Cells

1. Off Center: Glutamate has what effect?
2. Receptive field centers of the MIDGET BIPOLAR Cells are formed by what 2 things?
   a. What else?
3. Midget bipolar cells manifest what 2 things?

Answer 13

1. Opposite: Excitatory, and a reduction in its release, secondary to hyperpolarization of a photoreceptor, causes relative inhibition (hyperpolarization) of the Bipolar Cell
2. by L or M Cones
   a. S cone communicate w/a specific class of Bipolar Cells, referred to as S-CONE BIPOLAR CELLS
3. Both HIGH Spatial Resolution and Color Opponency

Question 14

On-center midget bipolar cell: Receptive field is made of what?

Answer 14

1. center made of a Single cone and the Surround by a mixture of L and M cones.

Question 15

On-center diffuse cell is made of what?

Answer 15

A mixture of L and M cones as well as the surround

Question 16

Amacrine cells

1. What do they show?
2. First Retinal Neurons to display what?
3. Tend to respond how?
   a. Though to play a critical role in what?

Answer 16

1. A Center-surround organization like bipolar cells
2. APs
3. Briefly, transiently, at the stimulus onset and offset.
   a. in Coding Movement

Question 17

1. As the diameter of a spot of light is increased, the ganglion cell manifests SPATIAL SUMMATION up to what?
   a. Results in what happening?
   b. Beyond this, what happens?

Answer 17

1. up to the PERIMETER of its receptive field center (On Center)
   a. Increase in frequency of APs
   b. Light falls onto the Antagonistic surround, causing a decrease in the Frequency of APs

Question 18

Strong stimulus for a Ganglion cell?

1. What are they selective for?

Answer 18

1. SPATIAL CONTRAST, but not Diffuse illumination. Contrast info is extracted form the visual scene very early in the visual system, w/in the retina itself

Question 19

Ganglion Cells

1. The Center-Surround organization found in ganglion cells has its origin in what cells?
   a. On-Center Midget Ganglion Cells synapse with what?
2. Midget Ganglion cells are referred to as what?
   a. Constitute what % of FOVEAL and NON-FOVEAL GANGLION CELLS?
3. On-Center diffuse Bipolar Cells synapse with what?

Answer 19

1. in Bipolar cells
   a. with On-center Midget bipolar cells (Off with off, on with on)
2. Retinal Parvo Cells
   a. 70%
3. On-center Parasol Ganglion cells. (off with off)

Question 20

1. S-Cone bipolar cells synapse onto what?
   a. % of ganglion cells?
2. The center of the ganglion cell is influenced by what?
   a. The surround is influenced by what?

Answer 20

1. Small Bistratified Cells
   a. 8%
2. Bipolar Cells
   a. Lateral Inhibition arising from Horizontal Cells

Question 21

1. Key feature of Central and Midperipheral Midget bipolar cells is the contribution of what to the Formation of the RECEPTIVE FIELD CENTER?
   a. This holds true for what else?
2. In peripheral retina: What happens?
   a. Each cone bipolar makes contact with what?

Answer 21

1. only 1 Cone
   a. For Midget Ganglion Cells located in the Fovea
2. More than 1 Bipolar Cell feeds into a Midget Ganglion Cell CENTER, resulting in LARGER RECEPTIVE FIELD CENTERS, increased Spatial SUMMATION and DECREASED SPATIAL RESOLUTION
   a. with B/w 1 and 10 cone photoreceptors, and rod bipolars contact 30-50 rods

Question 22

1. Parasol Ganglion cels (10%) respond how to a flash of light?
2. Midget ganglion cells will respond how to a flash of light?
3. Why the difference?

Answer 22

1. Transiently
2. Sustained response
3. may be due to the nature of the Amacrine Cell input, with parasol ganglion cells presumably receiving substantial input from transient amacrine cells and midgets receiving a large input from sustained amacrine cells.

Question 23

Biplexiform Cells

1. The only type of ganglion cell that connects to what?
   a. Role in vision?

Answer 23

1. That connects DIRECTLY to PHOTORECEPTORS

a. Unclear

Question 24

LGN

1. Each layer of LGN gets input from what?
2. Ipsilateral Eye
3. Contralateral Eye

Answer 24

1. ONLY ONE EYE
2. Layers 2,3 and 5
3. Layers 1, 4, and 6

Question 25

1. Ganglion cells adjacent in the retina will project to cells where?

Answer 25

1. ADJACENT in the LGN, forming an orderly map (RETINOTOPIC MAPPING)

Question 26

1. Parvo and Magno neurons account for what % of the Retinogeniculate Pathway 2. Konio cells what % 3. What neurons are characterized by color opponency?

Answer 26

1. 80% (70% parvo; 10% magno) 2. 10% 3. Parvo and Konio Neurons. This means they're excited by certain wavelengths and inhibited by others.

Question 27

1. Parvo: Smaller receptive fields: Support what better? | 2. Magno: Larger: support what?

Answer 27

1. Spatial Resolution (Better VA): Mostly connected to FOVEAL GANGLION CELLS 2. Greater Spatial Summation and Better Sensitivity in Low Light

Question 28

1. Parvo cells show what? 2. Parvocellular layers manifest what? 3. Konio cells exhibit what?

Answer 28

1. Inhibition (decreased AP frequency) for short wavelengths and excitation (increased rate) for long wavelengths: Color Opponency 2. Red-Green Opponency 3. Blue-Yellow Opponency * R-G and B-Y project to separate layers of the striate cortex

Question 29

1. What do magno neurons show?

Answer 29

1. Same spectral sensitivity in their Center surround, manifesting spatial Antagonism, but not color opponency

Question 30

1. Parvo cellular axon diameters are what? 2. Magno cellular neurons have what? 3. Large diameter cables transmit what?

Answer 30

1. smaller and they transmit electrical signals slower 2. Have larger diameter axons 3. transmit electrical signal faster. This would contribute to faster motion perception

Question 31

1. Transient responses to rapid changes in illumination gives what? 2. Parvo neurons manifest sustained responses when?

Answer 31

1. gives magno neurons the capability to resolve high temporal frequency stimuli 2. when presented with a long-duration stimulus: they respond to the stimulus for a relatively long period of time.

Question 32

1. Damage in Layers 3-6 (parvo cells) causes what? 2. Sensitivity to High-frequency flick is what? 3. Lesions in LGN Layers 1-2 (Magno cells) cause poor what?

Answer 32

1. reduced color perception and poorer visual acuity. 2. is preserved 3. poor detection of High-frequency flicker and greater difficulty in detecting large objects. Color perception and high spatial resolution are unaffected

Question 33

*Study slide 31

Answer 33

Study slide 31