Unit 1.6 and 1.7 From Eye to Brain and Striate Cortex

Question 1

What is the path of image processing from the eyeball to the brain?

Answer 1

1. Eye (vertical path)
   - photoreceptors
   - bipolar cells
   - retinal ganglion cells
2. lateral geniculate nucleus
3. striate cortex

Question 2

What is the Lateral Geniculate Nucleus (LGN)?

Answer 2

The LGN is a small structure located in the thalamus that serves as a relay station for visual information received from the retina via the optic nerve.

Question 3

How many lateral geniculate nuclei are there in the brain?

Answer 3

There are two lateral geniculate nuclei, one in each hemisphere of the brain.

Question 4

What types of layers are found in the lateral geniculate nuclei?

Answer 4

1. Magnocellular layers (1 & 2) - Large cells involved in motion processing.
2. Parvocellular layers (3-6) - Small cells that process details in static objects.
3. Koniocellular layers - Located between the parvo and magno layers, with different specializations.

Question 5

What is the function of the Magnocellular layers?

Answer 5

The Magnocellular layers are part of the parasol system and are responsible for detecting fast-moving objects.

Question 6

What is the function of the Parvocellular layers?

Answer 6

The Parvocellular layers are part of the midget system and are involved in processing fine spatial details and color.

Question 7

What is the role of the Koniocellular layers?

Answer 7

The Koniocellular layers have various specializations that contribute to visual processing, though their exact functions are still being explored.

Question 8

What is the topographical mapping of visual information in the LGN?

Answer 8

The LGN organizes visual information such that the left side of the visual field is processed in the right LGN and vice versa, with each layer receiving input from only one eye and creating a map of half of the visual field.

Question 9

What does “ipsilateral” and “contralateral” mean in the context of the LGN?

Answer 9

“Ipsilateral” refers to the same side of the body or brain, while “contralateral” refers to the opposite side. In the LGN, information from the same side of the visual field is processed contralaterally.

Question 10

What additional role does the LGN play beyond being a relay station?

Answer 10

The LGN also receives input from various other brain areas, functioning as a gate to the cortex and regulating visual information, especially during sleep.

Question 11

How does the LGN contribute to visual processing during sleep?

Answer 11

The LGN can shut off visual information while we sleep, which is related to its role in regulating sensory input and maintaining the brain’s focus on other functions.

Question 12

What is the significance of the optic chiasm in relation to the LGN?

Answer 12

The optic chiasm is where the optic nerves from each eye cross over. This crossing ensures that visual information from the left visual field is processed in the right hemisphere of the brain and vice versa, allowing the LGN to receive contralateral input.

Question 13

What happens to visual information after it leaves the LGN?

Answer 13

After processing in the LGN, visual information is projected to the primary visual cortex (striate cortex) via optic radiations, where further processing occurs.

Question 14

What is the striate cortex also known as?

Answer 14

The primary visual cortex or V1.

Question 15

How many cells are approximately in the striate cortex?

Answer 15

About 200 million cells.

Question 16

What are the two important features of the striate cortex?

Answer 16

Topographical mapping and dramatic scaling of information from different parts of the visual field.

Question 17

What is cortical magnification?

Answer 17

The phenomenon where 1 degree of visual angle at the fovea is processed by 15 times more neurons than 1 degree of visual angle just 10 degrees away from the fovea.

Question 18

What is the consequence of cortical magnification?

Answer 18

Images in the periphery have much lower resolution than images at fixation.

Question 19

What is visual crowding?

Answer 19

The deleterious effect of clutter on peripheral object detection, making it difficult to discern objects when other stimuli are nearby.

Question 20

Who were the researchers that discovered receptive fields in the striate cortex?

Answer 20

David Hubel and Torsten Wiesel.

Question 21

What are the two types of cells in the striate cortex that Hubel and Wiesel studied?

Answer 21

Simple cells and complex cells.

Question 22

What is the function of simple cells in the striate cortex?

Answer 22

Simple cells are neurons in the striate cortex that respond best to specific orientations of stimuli, such as bars of light, and their firing rate is dependent on the alignment of the stimulus with the receptive field.

Question 23

What is the role of complex cells in the striate cortex?

Answer 23

Complex cells respond to bars of light regardless of their exact position within the receptive field, indicating a broader range of responsiveness compared to simple cells.

Question 24

What is orientation tuning?

Answer 24

the tendency of neurons in the striate cortex to respond optimally to certain orientations, and less to others

Question 25

Where does each LGN cell respond?

Answer 25

to one eye or the other, but never to both

Question 26

What is ocular dominance?

Answer 26

Each striate cortex cell can respond to input from both eyes
- Ocular dominance refers to the preference of one eye over the other for visual input, leading to the suppression of the signal from the non-preferred eye.

Question 27

What is end stopping in the context of receptive fields?

Answer 27

End stopping is the process by which cells in the cortex first increase their firing rate as the bar length increases to fill up its receptive field, then decrease their firing rate as the bar is lengthened further

Question 28

What type of visual stimuli is often used in fMRI studies to assess sensitivity in the visual cortex?

Answer 28

Flickering checkerboard patterns.

Question 29

What is the significance of eccentricity in fMRI imaging of the visual cortex?

Answer 29

Eccentricity refers to the distance from the fovea in the visual field, and fMRI can show how sensitivity varies across different eccentricities.

Question 30

What is the primary purpose of fMRI imaging in the context of the visual cortex?

Answer 30

To map brain activity and understand which areas are activated in response to visual stimuli.

Question 31

What is a column in the context of the striate cortex?

Answer 31

A column is a vertical arrangement of neurons in the striate cortex that share similar properties, such as orientation preference.

Question 32

What is the distance over which all orientations are encountered in a column?

Answer 32

All orientations are encountered within a distance of about 0.5 mm in the striate cortex.

Question 33

What is a hypercolumn?

Answer 33

A hypercolumn is a 1x1 mm block of striate cortex that contains two sets of columns, each covering all orientations but with different ocular dominance.

Question 34

What is the significance of ocular dominance in hypercolumns?

Answer 34

Ocular dominance refers to the preference of certain neurons to respond more strongly to input from one eye over the other, which is organized within hypercolumns.

Question 35

What are “CO blobs” and their relevance to the striate cortex?

Answer 35

CO blobs are regular arrays of cells in the striate cortex that are involved in color processing and are arranged in a systematic columnar arrangement.

Question 36

How do columns in the striate cortex respond to visual stimuli?

Answer 36

Columns in the striate cortex respond optimally to specific orientations of visual stimuli, demonstrating selective responsiveness and orientation tuning.

Question 37

What is the relationship between columns and hypercolumns in terms of visual processing?

Answer 37

Columns within a hypercolumn work together to process visual information related to orientation and ocular dominance, contributing to the overall mapping of visual stimuli in the striate cortex.

Question 38

How does the organization of columns and hypercolumns contribute to visual perception?

Answer 38

The systematic organization allows for the processing of various visual features, such as orientation and color, which are essential for accurate visual perception and interpretation.

Question 39

What is the “pinwheel” model in relation to hypercolumns?

Answer 39

The “pinwheel” model illustrates how orientation preferences change smoothly across the cortical surface, with hypercolumns serving as centers for these preferences.