Chapter 10: The Central Visual System

2, 3, and 5; 1, 4, and 6

At the LGN, input from the two eyes is kept separate. In the right LGN the right eye (ipsilateral) axons synapse on LGN cells in layers _____; the left eye (contralateral) axons synapse on LGN cells in layers ______.

nasal retinas

At the optic chiasm, the axons originating in the _____ cross from one side to the other.

partial decussation

Because only the axons originating in the nasal retinas cross, we say that a _____ of the retinofugal projection occurs at the optic chiasm.

24

Beyond V1 lie another _____ distinct extrastriate areas of cortex that have unique receptive field properties.

primary visual cortex

Brodmann's area 17, located at the pole of the occipital lobe

pretectum

Direct projections from the retina to part of the midbrain, called the ______, control the size of the pupil and certain types of eye movements.

analysis of object motion

Direction-selective neurons are thought to be specialized for what?

ok

Draw the retinofugal projection.

six

Each LGN appears to be arranged in _____ distinct layers of cells bent around the optic tract like a knee joint.

analysis of object shape

For what are orientation-selective neurons thought to be specialized?

1. optic nerves 2. optic chiasm 3. optic tract

In order, what are the three components of the retinofugal projection?

commands eye and head movements to bring the image of this point in space onto the fovea

In the superior colliculus, there is a patch of neurons that, upon activation by a point of light, does what?

analysis of object color

It is generally believed that neurons sensitive to wavelength are important for what?

I

Layer _____ of the primary visual cortex, just under the pia mater, is largely devoid of neurons and consists almost entirely of axons and dendrites of cells in other layers.

VI

Layer _____ pyramidal cells give rise to the massive axonal projection back to the LGN.

calcarine fissure

Much of area 17 lies the medial surface of the hemisphere, surrounding the _____.

alertness and attentiveness; it powerfully modules the magnitude of LGN responses to visual stimuli

Synaptic inputs from the brain stem to the LGN relay information regarding what?

lateral geniculate nuclei

The _____ are the major targets of the two optic tracts.

pyramidal

The _____ cells send axons out of the striate cortex into the white matter.

LGN

The _____ is the gateway to the visual cortex.

dorsal; ventral

The _____ stream appears to serve the analysis of visual motion and the visual control of action. The _____ stream is thought to be involved in the perception of the visual world and the recognition of objects.

analysis of object color

The blob pathway might be involved in the _____.

I and II

The koniocellular LGN sends its axons to what layers of the striated cortex?

IVCα (4C alpha)

The magnocellular LGN sends its axons to what layer of the striated cortex?

analysis of object motion and the guidance of motor actions

The magnocellular pathway might be involved in the _____.

6; 9

The neocortex, in general, and the striate cortex in particular, have neuronal cell bodies arranged into about _____ layers (really _____).

analysis of fine object shape

The parvo-interblob pathway might be involved in the _____.

IVCβ (4C beta)

The parvocellular LGN sends its axons to what layer of the striated cortex?

true

True/False: All the information about the left visual hemifield is directed to the right side of the brain and vice versa.

true

True/False: Decussations are common in the sensory and motor systems.

true

True/False: Despite the distinct cytochrome oxidase labeling, at present there is no simple way to distinguish the receptive field properties of blob cells from neighboring interblob cells.

true

True/False: For the most part, each koniocellular layer gets input from the same eye as the overlapping M or P layer.

true

True/False: Only pyramidal cells send axons out of the striate cortex.

true

True/False: The visual receptive fields of LGN neurons are almost identical to those of the ganglion cells that feed them.

area MT

V5 (visual area 5)

the analysis of stimulus orientation

What appears to be one of the most important functions of the striate cortex?

Neurons that stain for cytochrome oxidase; they receive info from IVCβ and koniocellular LGN and send that info to other cortical areas.

What are blobs?

1. magnocellular pathway 2. parvo-interblob pathway 3. blob pathway

What are the three pathways in V1?

1. the mapping of the visual field onto a retinotopically organized structure is often distorted because visual space is not sampled uniformly by the cells in the retina 2. a discrete point of light can activate many cells in the retina, and often many more cells in the target structure, due to the overlap of receptive fields 3. perception is based on the brain's interpretation of distributed patterns of activity, not literal snapshots of the world

What are the three points to remember about retinotopy?

1. Brodmann's area 17 2. V1 3. striate cortex

What are three other names of the primary visual cortex?

1. navigation 2. directing eye movements 3. motion perception

What are three proposed roles of the motion-sensitive properties in the MST, MT, V1, and other areas?

area IT

What area is the farthest extent of visual processing in the ventral stream?

primary visual cortex (corticofugal feedback pathway)

What is the main source of synaptic input to the LGN?

tectum (specifically, the superior colliculus)

What is the major target of the retinofugal projection in all nonmammalian vertebrates?

to gate "bottom-up" input from the LGN to the cortex so that we may selectively pay attention to a portion of our visual field

What is the purpose of the corticofugal feedback pathway to the LGN?

direction-of-motion columns

What types of columns are present in area MT?

layers III, IVB, V, and VI

Where are spiny pyramidal neurons found in the striate cortex?

layer IVC

Where are spiny stellate neurons found in the striate cortex?

layers II and III in the striate cortex

Where are the cytochrome oxidase blobs located?

under the pia along the lateral surfaces of the diencephalon

Where do the optic tracts run?

layers III and IVB of V1

Where does information from the left and right eyes finally begin to mix?

at the base of the brain, just anterior to where the pituitary gland dangles

Where is the optic chiasm located?

geniculum

[Latin] small knee

fūgēre

[Latin] to flee

optic radiation

a collection of axons coursing from the lateral geniculate nucleus to the visual cortex

blob

a collection of cells (neurons), mainly in primary visual cortical layers II and III, characterized by a high level of the enzyme cytochrome oxidase

optic tract

a collection of retinal ganglion cell axons stretching from the optic chiasm to the brain stem; important targets of the optic tract are the lateral geniculate nucleus and superior colliculus

orientation column

a column of visual optical neurons stretching from layer II to layer VI that responds best to the same stimulus orientation

koniocellular LGN layer

a layer of the lateral geniculate nucleus containing very small cells, lying just ventral to each magnocellular and parvocellular layer; receives input from the nonM-nonP types of retinal ganglion cells

magnocellular LGN layer

a layer of the lateral geniculate nucleus receiving synaptic input from M-type retinal ganglion cells

parvocellular LGN layer

a layer of the lateral geniculate nucleus receiving synaptic input from P-type retinal ganglion cells

cytochrome oxidase

a mitochondrial enzyme concentrated in cells that form the blobs in primary visual cortex

retinofugal projection

a neural pathway that carries information from the retina to the superior colliculus

retinotectal projection

a neural pathway that carries information from the retina to the superior colliculus (about 10% of ganglion neurons in humans)

simple cell

a neuron found in primary visual cortex that has an elongated orientation-selective receptive field with distinct ON and OFF subregions

double-opponent cell

a neuron whose receptive field consists of both a color-opponent center and a color-opponent surround

saccade

a rapid movement of the eye between fixation points

ocular dominance column

a region of striate cortex receiving information predominantly from one eye

stereopsis

a term that is most often used to refer to the perception of depth and 3-dimensional structure obtained on the basis of visual information deriving from two eyes by individuals with normally developed binocular vision

optic tectum

a term used to describe the superior colliculus, particularly in nonmammalian vertebrates

lateral geniculate nucleus (LGN)

a thalamic nucleus that relays information from the retina to the primary visual cortex

complex cell

a type of visual cortical neuron that has an orientation-selective receptive field without distant ON and OFF subregions

area V4

an area of neocortex, anterior to striate cortex, that is in the ventral visual processing stream and appears to be important for both shape perception and color perception

area MT

an area of neocortex, at the junction of the parietal and temporal lobes, that receives input from primary visual cortex and appears to be specialized for the processing of object motion

area IT (inferior temporal)

an area of neocortex, on the inferior surface of the temporal lobe, that is part of the ventral visual processing stream; contains neurons with responses to complex objects, including faces, and appears to be involved in visual memory

achromatopsia

characterized by a partial or complete loss of color vision despite the presence of normal functional cones in the retina

prosopagnosia

difficulty recognizing faces even though vision is otherwise normal

radially

in a manner perpendicular to the surface

superior colliculus of the tectum

involved in generating saccadic eye movements

inhibitory neurons

neurons that lack spines in the striate cortex and are found in many of the cortical layers

optic nerve

the bundle of ganglion cell axons that passes from the eye to the optic chiasm

decussation

the crossing of a fiber bundle from one side of the brain to the other

visual hemifield

the half of the visual field to one side of the fixation point

binocular visual field

the portion of the visual field viewed by both eyes

orientation selectivity

the property of a cell in the visual system that responds to a limited range of stimulus orientations

direction selectivity

the property of cells in the visual system that respond only when stimuli move within a limited range of directions

binocular receptive field

the receptive field of a neuron that responds to stimulation of either eye

optic chiasm

the structure in which the right and left optic nerves converge and partially decussate (cross) to form the optic tracts

retinotopy

the topographic organization of visual pathways in which neighboring cells on the retina send information to neighboring cells in a target structure

visual field

the total region of space viewed by both eyes when the eyes are fixated on a point

cortical module

the unit of cerebral cortex that is necessary and sufficient to analyze one discrete point in a sensory surface