Download visual fields

Functional and Dysfunctional Anatomy of
Visual Cortex
Emily A UlmerA, Stephanie M. FranczakB, Edgar DeYoe PhDC,
Andrew P Klein MDC, Leighton P Mark MDC
University Lake School, Hartland, WIA
Divine Savior Holy Angels, Milwaukee, WIB
Medical College of Wisconsin, Milwaukee, WIC
Purpose: The purpose of this exhibit is to demonstrate functional brain
anatomy and deficit localization of vision cortex.
Overview: Visual field topography is preserved on the retina, through visual
pathways, and in the visual cortex. Functional brain mapping reveals the
retinotopic organization of the visual cortex and can be used to understand and
predict the location of scotoma. Divergent hierarchical and parallel processing
of visual stimuli attributes generates the perception of color, form, motion and
position. A ventral processing stream provides information to the temporooccipital visual area, or the “What Area,” for visual object and color
recognition processing. A dorsal processing stream provides information to the
parietal visual area, or the “Where Area,” for higher visuospatial and attention
processing. Each processing stream has multiple functional sub-streams and
numerous interconnections. This tutorial reviews the functional organization of
the visual system and associated deficits.
For a more thorough review on the topic, see:
1.
2.
DeYoe, EA, Raut RV. Neuroimaging Clinics 24.4, Clinical Applications of Functional MRI,
Elsevier, November 2014. Visual Mapping Using Blood Oxygen Level Dependent FMRI pg
573-584.
Jonathan D. Trobe, The Neurology of Vision Oxford University Press March 2001.V.
Overview
The visual system engages in significant computational processing to transform
simple retinal images and sensory cues, to infer attributes about the physical world
Retinal images Sensory Cues (V1)
Image
 Intensity
 Wavelength
 Time
 Position
 Eyes (R,L)
Primary
 Luminance
 Spectral
Inferred Attributes (extrastriate cortex)
3D form
 Shape
 Size
 Rigidity
Feature-based
 Contrast
Surface properties
 Disparity
 Color (brightness, hue, saturation)
 2-D velocity  Visual texture
 2-D orientation  Specular reflectance
 Transparency (shadows &
highlights)
V1 = 1o visual cortex
Extrastriate = association visual cortex
3-D spacial relationships
 Relative positions (X,Y,Z)
 3-D orientation in space
3-D movement
 Trajectory
 Rotation
What is it?
Temporal
visual cortex
Where is it?
Parietal
visual cortex
Take a minute to review the major visual pathways and functions
Geniculostriate system
Retinotectal system (see Agarwal et al., EdE Conscious visual perception
41, Neural Control of Ocular Movements)
 Pathway: Retina
lateral geniculate nucleus (LGN)
 Directing eye movements and visual
striate cortex
extrastriate cortex
attention
 Pathway: Retina
superior colliculus
pulvinar
extrastriate cortex
Geniculostriate and Retinotectal Visual Systems
Temporal half of right retina
Nasal half of left retina
Retina
Meyer's loop
Lateral
geniculate body
(nucleus)
Medial geniculate body
Pulvinar
Extrastriate
cortex
Optic radiations
(in retrolenticular
limb of internal
capsule)
Right
lateral
geniculate
nucleus
Brachium of sup. colliculus
Superior
colliculus
Striate
cortex
Visual cortex of
right hemisphere
Visual reflex pathways (see Agarwal et al.,
EdE-41, Neural Control of Ocular
Movements)
 Accommodation (focusing the eye):
Controls muscles of the ciliary body via
a pathway through the cortex,
pretectum, and ciliary ganglion.
Contraction of the ciliary muscle causes
thickening of the lens.
 Pupillary control of light intensity:
 Constriction: Retinal signals control
pupillary constrictor muscles via
pathways through the pretectum,
Edinger-Westphal nucleus, and ciliary
ganglion
 Dilation: Retinal signals control
dilator muscles via pathways through
the spinal cord and superior cervical
ganglion
Fibers emanating from the LGN forming the optic radiation
 Optic radiation:
Chiasm
Optic
tract
Meyers
loop
tract
LGN
Radiations
Visual
cortex
 Projects from the LGN to the primary visual
cortex (V1)
 Passes through the posterior (retrolenticular) aspect of the posterior limb IC
 Superior fibers course backward toward
the occipital lobe
 Inferior fibers course antero-inferiorly
around the temporal horn before turning
backwards (Meyer`s loop)
 Optic radiation maintains retinotopic
organization
Now that you have reviewed the geniculostriate
pathway, try your luck at predicting visual field
deficits. Click once for the lesion and a second time
for the deficit.
RIGHT EYE
LEFT EYE
VISUAL FIELDS
LEFT
RIGHT
Total blindness - Right eye
Left superior quadrantanopia
Optic nerve
Bitemporal hemianopia
Optic chiasm
Optic tract
Chiasm
Optic
tract
Meyers
loop
tract
Geniculocalcarine tract
or optic
radiations
Left homonymous hemianopia
Lat. geniculate body
LGN
Left homonymous superior
Meyer’s
quadrantanopia
Loop has
fibers from
both eyes
Radiations
Primary visual cortex (area 17)
Visual
cortex
Left homonymous hemianopia
(macula spared)
Topography of the Visual System
Visual field
Topography of the Visual System & Cortical Magnification
Retina
Uncrossed
fibers
Crossed
fibers
A
B
LGN
Topography of the visual system
Overlapping
visual fields
Projection on
right retina
Left
retina
Projection on
left lateral
geniculate
body
Optic nerve
Optic tract
Optic chiasm
Lat. geniculate body
Projection on
right LGN
Calc.
fissure
Projection on left
occipital lobe
Geniculocalcarine
(optic) radiation
Occipital
Lobe
 Preserved topography
 Visual field topography is preserved on the
retina
 The topography of the receptor array (retina)
is preserved in the LGN
 The retinotopic organization of the LGN is
maintained in the visual cortex
 Foveal magnification
 Foveal vision is magnified in the LGN and
primary visual cortex
 Magnification changes from 4 mm/degree to
0.5 mm/degree as the visual representation
moves from 1o to 25o away from the center
of gaze
 One central degree of visual field is
represented by 64 times the area of cortex
than that devoted to the peripheral visual
field
 Foveal vision is represented in the cortex of
the occipital pole
Divergence of Hierarchical Visual Processing
 There is hierarchical (more complex)
processing of visual stimuli attributes
from retina to higher-order visual areas
 There is a relative divergence of
processing of attributes (i.e. color, form,
motion and position)
 Ventral processing stream
 Temporal visual area
 Object /word/face/place
recognition
 “What area”
 Dorsal processing stream
 Parietal visual area
 Visuospatial processing and
visual attention
 “Where area”
 Each processing stream has multiple
functional sub-streams with numerous
interconnections
The primary visual cortex (V1) is centered around the calcarine sulcus. Hierarchical
processing occurs in association cortex along dorsal (parietal) and ventral (temporal)
processing streams, becoming ever more complex
Spatial relations
Visual attention
Motion
Identification
Visual memory
The type of visual deficit present depends
on the location of the cortical lesion
 Deficits:
 V1, V2 – complete blindness of
visual information
 Occipital pole – central visual field
deficit
 Closer to parieto-occipital sulcus
(POS) – peripheral visual field
deficit
 Higher visual areas – loss of
different types of visual
information processing such as
shape, color, motion, and/or
position
 Specific deficits affected by
involvement of dorsal or ventral
processing streams
Ventral Stream Visual Deficits
 Deficits of the ventral stream
(ventral temporal area - VTA)
 Visual object agnosia
 Bilateral but left >right TVA
 Prosopagnosia (faces)
 Bilateral or right >>left TVA
 Pure word alexia
 Left TVA
 Contralesional achromatopsia (lack of
color recognition)
 V4/VO
 Color anomia (naming colors)
 Left TVA
 Visual amnesia
 Bilateral or right >>left
Dorsal Stream Visual Deficits
 Deficits of the dorsal stream
(Parietal visual area - PVA)
 Hemispatial neglect
 Right >>>Left PVA/angular gyrus,
or frontal lobe, or pulvinar
 Bilateral inattention
 Bilateral PVA
 Acquired ocular motor apraxia
 Bilateral PVA
 Optic ataxia
 Usually bilateral >> unilateral
PVA
 Impaired spatial relations
 Right >>>left parieto-occipital
 Akinetopsia
 Bilat. hMT (Occ-temp-pariet jxn)
Retinotopic Mapping of Visual Cortex
The retinotopic organization of the visual cortex
can be mapped
with fMRI: Eccentricity
Mapping eccentricity in 3 subjects
3D
Flat Map
The retinotopic organization of the visual cortex
can be mapped with fMRI: Polar Angle
Polar angle mapping in 3 subjects
3D
Flat Map
Functional field maps can be constructed from eccentricity and polar
angle coordinates, relating activation to visual field locations
Composite eccentricity and polar angle maps can
localize functional visual cortical areas
Cases: Apply Your Knowledge
48 yo with right visual field cut
Where is the infarct? (choose one)
A. Right thalamus (MGN)
B. Left thalamus (MGN)
C. Right medial occipital lobe
D. Left medial occipital lobe
48 yo with right visual field cut
 D. Left medial occipital lobe
Sulcal effacement
48 yo with right visual field cut
deficit
may occur
at several
 AD.visual
Leftfield
medial
occipital
lobe
locations along the visual pathway. Tracing
the pathways on CT in this case revealed
subtle left occipital sulcal effacement,
suggesting an infarct accounting for the
contralateral visual deficit.
Visual Field
Deficits
Lesions of the Visual Pathways
3
1
Monocular Blindness
2
Monocular Blindness and
(Chiasm)
1
Meyers’ Loop
4
Optic Nerve
2
Superior Quadrantopia
Optic Tract
3
Bitemporal Hemianopia
5
LGN
4
Homonymous
Hemianopia
Optic Radiation
5
Homonymous Superior
Quadrantanopia
Homonymous Hemianopia
6
Visual Cortex
6
(macula spared)
68 yo with right visual field deficit
Where is the acute infarct?
(choose one)
A. Right corona radiata
B. Right putamen
C. Left posterior limb IC
D. Left thalamus
68 yo with right visual field deficit
 C. Left posterior limb internal capsule
68 yo with right visual field deficit
 C. Left posterior limb internal capsule (PLIC)
The infarct is located in the retrolenticular portion of the internal
capsule (bordering the posterior
putamen), corresponding to anterioposterior orientation of fiber bundles
(green) at DTI. This area contains
portions of non-motor fiber tracts
such the optic radiation, the acoustic
radiation, and is adjacent to
somatosensory fibers. Thus, an infarct
here may cause deficits in vision and
audition, and somatosensory
perception.
Retrolenticular
portion of
the PLIC
Retrolenticular
portion of
the PLIC
59 yo RH patient with a ventral temporo-occipital infarct
What is the most likely deficit?
(choose one)
A. Right hemi-spatial neglect
B. Visuomotor dysfunction
C. Optic ataxia
D. Visual agnosia
59 yo RH patient with a ventral temporo-occipital infarct
 D. Visual agnosia
Higher visual processing occurs along
hierarchical dorsal and ventral
processing streams. The temporal
visual area (ventral processing stream)
compares what one sees to visual
memories, to provide recognition of
objects, faces, places, and words
(dominant hemisphere). Infarcts of the
ventral visual areas may cause a class
of deficits known as agnosias.
Agnosia is the inability to recognize
objects, places, faces, as well as words
in the dominant hemisphere.
Visual spatial,
visual motor,
visual attention
Object, word,
place, face
recognition
53 yo with an occipital infarct
What is the most likely deficit?
(choose one)
A. Left hemianopia
B. Left upper quadrantanopia
C. Left lower quadrantanopia
D. Agnosia
53 yo with an occipital infarct
 C. Left lower quadrantanopia
The infarct is located in the supracalcarine visual cortex (cuneus),
C
which processes visual information
from the lower visual field. Thus, a
unilateral supra-calcarine occipital
cortex infarct will result in a
Calcarine contralateral lower quadrantanopia.
Cuneus
infarct
sulcus
fMRI
59 yo right handed patient with a right parietal infarct
What is the most likely deficit?
(choose one)
A. Left hemianopia
B. Left hemispatial neglect
C. Aphasia
D. Agnosia
59 yo right handed patient with a right parietal infarct
 B. Left hemispatial neglect
Hierarchical visual processing occurs along
dorsal and ventral processing streams. Parietal
visual areas (dorsal processing stream)
process visual spatial and visual motor
information, as well as support attention to
visual stimuli. Cortex of the inferior parietal
lobule is responsible for visual attention. The
left parietal visual area (PVA) supports
attention to the right visual hemi-field while
the right PVA supports attention to both visual
hemi-fields. Consequently, left PVA infarcts
rarely cause hemi-spatial neglect, because the
right PVA supports both hemi-fields. Right
PVA infarcts on the other hand may cause left
hemi-spatial neglect. It should be noted,
however, that recent studies have questioned
this classic model and suggest the
organization may be more complex. Stay
tuned…
Visual spatial,
visual motor,
visual attention
Object, word,
place, face
recognition
8 yo female with refractory right hemispheric seizures and visuospatial dysfunction.
Where is the abnormal cortex likely to be? Click once for answer
8 yo female with visuospatial dysfunction,
Answer: Right parietal visual area
PET
Based on cortical retinotopy, what visual field deficits are at risk?
What visual field deficits are at risk? Click once for answer
Answer: Peripheral vision is at risk along the posterior tumor border
Eccentricity
What visual field deficits are at risk? What about white matter?
Answer: Central and peripheral vision is at risk along the lateral border
Eccentricity
DTI
Optic
radiation
Conclusions
 Understanding visual system functional and
dysfunctional anatomy improves the accuracy of
Neuroradiologic interpretations at standard MRI
 Understanding visual system functional anatomy
improves utilization of fMRI and DTI for presurgical
planning
 Understanding the effects of lesions on vision
function provides a framework by which to guide
surgical decision-making