organization of human visual cortex

8/6/2019 Organization of Human Visual Cortex

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Organizationof Human Visual

Cortex

Presented by

Gamal Taha EL-SayedAssistant lecturer of Anatomy & Embryology

Ain Shams University


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Organization of Human Visual

Cortexy The human visual system contains

numerous visual areas that collectively

occupy about 27% of the total extent ofcerebral cortex (950 cm2).

yVisual areas will be classified and reviewedin four sections: occipital visual areas,ventral stream areas, dorsal streamareas, and frontal areas.


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Cortex

y D

rawing byLeonardo DaVinci of

the projection of the

eyes to the ventriclesof the brain.


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Cortex


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Cortex


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Occipital visual areasOccipital visual areas

y Primary Visual Cortex:

y

Area V1 (also known as primary visual cortex

,striate cortex, or Brodmanns area 17) is the

human visual cortical area with the most

well-defined anatomical boundaries.

y This area processes strong orientation and

direction selectivities.


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y Generally the upper lip of the calcarine

sulcus responds to the lower half of visual

field, and the lower lip of the calcarine

responds to the upper half of visual field.

y The horizontal meridian in the visual field is

mapped onto the base of the calcarinesulcus, while the vertical one spreads

between V1 & V2.


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Cortex


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y Pathological damages to V1 usually lead to

scotomas (e.g., hemianopia) restricted to

corresponding regions of the visual field.

y Interestingly, patients with scotomas are

often able to make use of visual information

presented to their scotomas, despite beingunable to consciously perceive it a

phenomenon called blindsight.


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y Areas V2-V3-VP:

y V2 (Brodmanns area 18) and V3

(Brodmanns area 19) are located adjacent

to V1 and are part of extrastriate cortex,

sometimes called the peristriate belt.

y As in V1, V2 and V3 have well-definedtopographical representations of the

contralateral visual hemifield


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y Each area has a dorsal part (V2d and V3d,

above the calcarine fissure representing the

lower visual field) and a ventral part (V2v

and V3v/VP, below the calcarinerepresenting the upper visual field).

y V1, V2, and V3 share a common foveal region(foveal confluence) near the occipital pole.


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y Functionally, V2 and V3 have many properties

in common with V1. Cells are tuned to

simple properties such as orientation,

spatial frequency, and color.

y FMRI suggests that human V2 may be

relatively sensitive to the illusory contours.


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Cortexy Illusory contours (ICs)

y A classic example of an IC is the illusory

square, where four sectored discs oriented

in an appropriate manner generate the

percept of a square. In this instance it is

clear that no true luminance differencesexist to form a complete square and yet a

square is perceived.


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Cortex


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y The Human Color Center

Areas V4-V8:

y Neuro-imaging studies have also shown regionsin the vicinity of V4v that respond morestrongly to colored patterns than toluminance defined patterns.These regions are

referred to as V8.

y Clinical studies reveal that color vision loss(achromatopsia) is correlated with damage in

these areas.


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yMotion Perception,

Area V5 (Human MT):y Human MT(hMT) is located at the

temporo-parietal occipital junction.

y This region is a central motion-selective

locus in the human brain. hMTis selectivelyactivated by movingversus stationary

stimuli and exhibits high contrast sensitivity


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y Area V5 (Human MT):y Activation of this area is enhanced when

subjects attend toor trackmotion.

y Increasing evidence also suggests a distinct

area in the superior-temporal sulcus

specialized for perceiving biological

motion, such as movies of people walking or

of hand, eye, or mouth movement.


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y Areas V3A-V3B:

y Discovered between V3 and V4 areas.

y Human V3A has a distinctive, continuous

map of the entire contra-lateral hemi-field

immediately anterior to area V3


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y Areas V3A-V3B:

y V3A has large receptive fields which are

apparently involved in widefieldvisual

computations. Such calculations include the

processing of binocular disparity and illusory

contours and Depth Perception.


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y Area V7:

y Anterior to V3A, V7 has a distinct foveal

representation and its related to saccadic

eye movements.


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Cortex


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Can u read thisCan u read thisy Olny srmat poelpe can raed this.I cdnuolt blveiee that I cluod

aulaclty uesdnatnrd what I was rdanieg.The

phaonmneal pweor of the hmuan mnid,

aoccdrnig to a rscheearch at Cmabrigde

Uinervtisy, it deosn't mttaer in what oredr the

ltteers in a word are, the olny iprmoatnt tihng is

that the first and last ltteer be in the rghit pclae.The rset can be a taotl mses and you can still

raed it wouthit a porbelm. This is bcuseae the

huamn mnid deos not raed ervey lteter by istlef,

but the word as a wlohe.


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y Ventral StreamAreas:

y Cortex anterior to V4 (infero-temporal

cortex) is generally considered part of theventral processing stream.

y It shows functional specialization in objectrepresentation and recognition, so thatdamage to these regions results in severevisual recognition deficit or agnosia seeing

without knowledge.


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Organization of Human VisualCortex


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y Dorsal StreamAreas:

y Present in the posterior parietal cortex, it is

responsible for the gathering of visual

information to make decisions about where

an object is located. This information is then

transferred to the somato-sensory cortexwhere decisions regarding proper motor

actions are made.


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y Dorsal StreamAreas:

yOptic ataxia is a disorder of the dorsal

stream where people experience difficulty in

reaching for objects in a goal oriented

task. It is a visuo-motor deficit where the

perception of object location in space isintact, but the patient is unable to perform

the required movements to interact with

the object.


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y Lateral Occipital Complex:

y A complex of multiple areas in lateral

occipital cortex that responds more

strongly to a varietyofobject shapes, as

compared with textures, noise patterns,

scrambled objects.


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y Fusiform FaceArea:

y Neuroimaging studies have shown a specific

region within the fusiform gyrus that is

significantly more active when viewing

faces.

y The FFA shows a higher response to

upright than inverted faces


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y Parahippocampal PlaceArea:

y Responds preferentially to indoor/outdoor

scenes and also to houses/buildings, but

not to faces or objects.


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y Extrastriate BodyArea:

y A distinct cortical region in humans that

responds selectively to images of non face

body parts.

y This region is located in the lateral occipito-temporal cortex, adjacent to motion-

selective MT/MST area.


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y Caudal Intraparietal Sulcus:

y Human neuro-imaging has identified a region

in the caudal end of the intraparietal sulcus

that is activated during stereoscopic

processingduring object matching and

grasping as well as during discriminationsofobject size and surface orientation


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y Parieto-Occipital Cortex/V6:

y Located in the parieto-occipital sulcus

(anteromedial cuneus) Human V6 responds

strongly to luminance flicker.


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y Parietal Reach Region:

y Neuroimaging studies have also reported

activation in the human intraparietal sulcus

during reachingandpointingmovements


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y AnteriorIntraparietalArea:

y The human anterior intraparietal sulcus is

also activated during visually guided

grasping.

y Studies have reported that this region is alsoactivated by action observation like mental

rotation and tactile manipulation of objects.


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y Ventral IntraparietalArea:

y Present in the depth of the human IPS thatresponds multimodally to visual, tactile,

and auditorymoving stimuli.

y This region is also activated by 3Dstructure frommotion.


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y Lateral IntraparietalArea:

y In the posterior IPS,This region is active

when humans make visually guided eye

movements.

y In addition, recent studies have shown thatthis region in the IPS is jointly activated by

attending, pointing, and making saccades to

peripheral targets.


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y Superior Parietal Lobule andInferior

Parietal Lobule:

y So far, the precise role of these parietal

regions in attention is a matter of substantial

debate; however, several studies have

strengthened the evidence that regions inparietal cortex (particularly SPL and in some

cases IPL) are a source ofattentional

control signals.


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y FrontalAreas:

y Areas 8 (FEF: frontal eye field) and 46 as

part of visual cortex. However, little is

known about the visual properties of frontal

and prefrontal cortical areas in humans.

Recently, one study has shown that workingmemory-related areas in human dorso-

lateral prefrontal cortex contain a

topological map of visual space


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SummaryArea Place Function

1 Area V1Calcarine fissure and

beyond the Lunate

sulcus

Orientation and

Direction Selectivities.

2Areas V2-

V3

Above and below

the calcarine fissure

Orientation, Globalmotion and illusory

contours

3Areas V4-

V8

Posterior to

posterior infero-

temporal area

Color Center

4Area V5

(Human MT) Temporo-parietaloccipital junction Motion Perception5

Areas V3A-

V3B

Between V3 andV4

areasDepth Perception


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6 Area V7 Anterior to V3ASaccadic eye

Movements.

7

Ventral

Stream

Areas

Infero-temporalcortex

Object Representationand Recognition

8

Dorsal

Stream

Areas

Posterior parietal

cortex

Informations about

where an object is

located

9

Lateral

Occipital

Complex

Multiple areas in

lateral occipital

cortex

Variety of Object

Shapes

10Fusiform

FaceAreaFusiform gyrus Viewing Upright Faces


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11

Para-

hippocampal

PlaceArea

Para-hippocampal

gyrusIndoor/Outdoor scenes

12

Extra-

striate

BodyArea

Lateral occipito-temporal cortex

Images of non FaceBody parts

13

Caudal Intra-

parietal

Sulcus

Caudal Intra-

parietal SulcusStereoscopic

Processing

14

Parieto-

Occipital

Cortex-V6

Parieto-occipital

sulcus

(anteromedial

cuneus)

Luminance Flicker


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15

Parietal

Reach

RegionIntraparietal sulcus

Reaching and pointing

movements

16

Anterior

Intra-parietal

AreaHuman anterior

intraparietal sulcusVisually guided

grasping.

17

Ventral

Intra-parietal

AreaIntraparietal sulcus

3D Structure from

motion.

18Lateral Intra-

parietalArea

PosteriorIntraparietal sulcus

Visually guided eye

movements.


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Thank you

organization of human visual cortex

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