Module 6

Question 1

• After the chiasm → optic tracts

Answer 1

o ~90% go to the lateral geniculate nucleus (LGN)
o Others go to the superior colliculus (involved in reflexive eye movements)

Question 2

LGN pathway

Answer 2

Projection to Primary Visual Cortex: From the LGN, signals travel through the optic radiations to reach area V1, where cortical processing of visual information begins.

Question 3

Lateral Geniculate Nucleus
Layered Anatomy

Answer 3

1. Magnocellular layers (1–2): large cell bodies.
2. Parvocellular layers (3–6): smaller cell bodies.
3. Koniocellular layers: very small cells, one thin layer beneath each of the six main layers.

Question 4

LGN Layer → V1 Ocular Dominance Mapping

Answer 4

Contralateral eye → LGN layers 1, 4, and 6 (plus their intercalated koniocellular layers) → V1 ocular-dominance columns driven by the contralateral eye.

Ipsilateral eye → LGN layers 2, 3, and 5 (plus their intercalated koniocellular layers) → V1 ocular-dominance columns driven by the ipsilateral eye.

Question 5

Ganglion-cell pathways

Answer 5

Parasol RGCs → magnocellular layers
Midget RGCs → parvocellular layers
Bistratified RGCs → koniocellular layers

Question 6

Functional Specialization

Answer 6

Magnocellular: high sensitivity to motion and flicker.
Parvocellular: high sensitivity to static features (color, texture, form, depth).
Koniocellular: also contributes to color processing.

Question 7

SC Function

Answer 7

Function
* Controls saccades (rapid eye movements toward visual targets)
* Focuses on “where”, not “what”

Question 8

SC Neuron Properties

Answer 8

• Respond to any visual stimulus, regardless of shape/color
• Fast response after eye → enables quick gaze shifts

Question 9

Multisensory Integration

Answer 9

• SC also gets auditory and somatosensory input
• Can combine weak signals across senses for stronger response

Question 10

• Optic nerves meet at the optic chiasm. What happens there?

Answer 10

Nasal fibers cross sides
Temporal fibers stay on the same side (ipsilateral)

Question 11

Non-Geniculate Pathway

Answer 11

• SC sends visual input directly to extrastriate cortex, bypassing V1
• Explains blindsight: V1-damaged patients can act visually without awareness

Question 12

What defines a simple cell’s receptive field in V1 and how does it respond?

Answer 12

It has an elongated excitatory stripe flanked by inhibitory zones; it fires maximally to a bar of light in its preferred orientation at its specific retinal location.

Question 13

How do simple cells resolve the ambiguity between orientation and contrast?

Answer 13

A population of co-localized simple cells, each tuned to a different orientation, compares relative firing rates—this population code lets the brain infer orientation independent of contrast.

Question 14

Simple Cells Circuitry

Answer 14

Circuitry: Simple cells receive convergent input from multiple
LGN cells with circular center-surround receptive fields, aligned with the cell’s preferred orientation:

Aligned bars activate excitatory centers, causing strong firing;
misaligned bars activate inhibitory surrounds, reducing firing

Question 15

Complex Cells

Answer 15

More numerous than simple cells in V1. Also tuned for orientation but
contrast-polarity invariant: respond equally to light-on-dark and dark-on-light bars. Position invariant within their receptive field: respond to their preferred orientation anywhere
inside it.

Question 16

Three Columnar Organizational Maps in V1

Answer 16

Three Columnar Organizational Maps in V1.
Ocular Dominance Columns:
Neurons grouped by predominance of input from one eye (contralateral vs. ipsilateral).2.
Orientation Columns:
Neurons tuned to similar edge orientations arranged in vertically aligned slabs.3.
Retinotopic Mapping:
Columns correspond to specific retinal locations; adjacent columns represent adjacent regions of visual space.

Question 17

Retinotopic Mapping

Answer 17

V1 arranged so that neighboring cortical columns correspond to
neighboring locations in the visual field. Perpendicular electrode insertions encounter neurons with overlapping receptive fields at the same retinal location. Oblique penetrations
traverse columns
with receptive fields stepping across
adjacent retinal positions

Cortical Magnification:
Nonuniform representation of visual space in V1: central (foveal) vision occupies disproportionately
more cortical area
than peripheral vision. Due to
high RGC density and small receptive fields in the fovea versus lower density and larger receptive fields in the periphery.

Supports high visual acuity centrally; fewer V1 neurons represent each degree of peripheral visual angle.

Question 18

Bistratified RGCs

Answer 18

→ Koniocellular layers → V1 layers 2/3 (blobs)

Question 19

V1 blobs (2 and 3)
: color processing

Answer 19

: color processing

Question 20

V1 interblobs (2 and 3): form processing

Answer 20

form processing

Question 21

V2 bands:

Answer 21

Thin bands: color
Pale bands: form
Thick bands: motion

Question 22

“What” (Ventral) Pathway

Answer 22

V1 4Cβ & blobs → V2 thin/pale bands → V4 → Inferotemporal cortex
Carries form & color information for object recognition

Question 23

Where/How” (Dorsal) Pathway

Answer 23

V1 4Cα → V2 thick bands → MT (V5) → Parietal cortex
Carries motion & spatial location information for visual–motor interaction

Question 24

Q: What is the sequence of the Parasol (Magnocellular) pathway from retina to cortex, and what does it process?

Answer 24

Parasol
Magnocellular
4Cα
Thick (motion)
MT (motion)
Parietal cortex( perceiving space and motion; coordinatingvisual-motor interactions)
Dorsal”Where”/”How

Question 25

Q: What is the sequence of the Midget (Parvocellular) pathway from retina to cortex, and what does it process?

Answer 25

Midget Parvocellular 4Cβ Thin (color),Pale (form) V4 (form, color) Inferotemporalcortex (objectrecognition) Ventral "What"

Question 26

What is the sequence of the Bistratified (Koniocellular) pathway from retina to cortex, and what does it process?

Answer 26

Bistratified Koniocellular 2/3 (blobs) Thin (color)

Question 27

Q: What are the key functions of Area V4 in the ventral “What” pathway, and what happens if it’s damaged?

Answer 27

Selective for color hues and edge curvature Damage leads to achromatopsia (cortical color blindness)

Question 28

Which regions constitute the Lateral Occipital Cortex & Inferotemporal (IT) Cortex, and what specialized modules do they contain?

Answer 28

Respond to complex object shapes (tools, animals, etc.) with large, position-invariant receptive fields Fusiform Face Area (FFA): face recognition Parahippocampal Place Area (PPA): large-scale scenes and places

Question 29

What is the role of Area MT (V5) in the dorsal “Where/How” pathway, and what are the effects of its damage?

Answer 29

Tuned for the direction and speed of motion Damage causes impaired motion perception (akinetopsia)

Question 30

Which subregions of the Intraparietal Sulcus (IPS) are involved in visually guided actions, and what do they specialize in?

Answer 30

Lateral IPS (LIP): eye movements and attention Medial IPS (MIP): reaching movements Anterior IPS (AIP): grasping actions All located in the parietal lobe on the dorsal pathway.

Question 31

Face Recognition Hemispheres

Answer 31

Face Recognition Upright–Face Detection & Discrimination: Right hemisphere specialized for detecting upright faces and discriminating among similar faces. Left hemisphere poor at fine discrimination but can use verbal labels to tell apart dissimilar faces (e.g. “blonde vs. brunette”). Familiar-Face Recognition: Right hemisphere more accurate than left in recognizing familiar faces overall. Split-brain and lesion studies reveal nuanced lateralization: the right hemisphere often excels at block-design tasks and face discrimination, while the left better recognizes self-faces and controls voluntary facial expressions.

Question 32

How are voluntary facial expressions controlled and what is their neural pathway?

Answer 32

Controlled by the left hemisphere. Pathway: left motor cortex → right facial nucleus (CN VII) → right facial muscles, plus callosal signal to right hemisphere → left facial nucleus → left facial muscles. Produces symmetrical deliberate movements (e.g., a voluntary smile).

Question 33

How are spontaneous facial expressions generated and what distinguishes their pathway?

Answer 33

Can be triggered by either hemisphere. Pathway: noncortical midbrain circuits → brainstem nuclei → facial muscles. Evolutionarily older system shared with nonhuman primates; not under direct cortical (voluntary) control.

Question 34

Primary Somatosensory Cortex (S1)

Answer 34

Situated in the postcentral gyrus (Brodmann areas 1–3), S1 contains a finely organized somatotopic map—the “sensory homunculus”—that allocates cortical territory according to tactile acuity. Regions of high functional importance (e.g., the hands and face) occupy disproportionately large areas compared to less sensitive zones (e.g., the trunk), a phenomenon known as cortical magnification.

Question 35

Secondary Somatosensory Cortex (S2)

Answer 35

Located ventral to S1, S2 integrates inputs from both hemispheres via the corpus callosum to build higher-order representations of object texture, shape, and size. This bilateral convergence underlies our ability to perceive and coordinate bimanual touch.

Question 36

Achromatopsia:

Answer 36

Central color blindness from V4 lesions; patients see in gray yet retain luminance perception, with sometimes quadrant-specific deficits