Extrastriate Cortex and
Higher Cortical Deficits
Adler’s Physiology of the Eye 11th Ed.
Chapter 31 - by Boyd & Matsubara
http://www.mcgill.ca/mvr/resident/
Multiple Visual Areas Beyond V1
Monkey Brain
Extrastriate Cortex
• Discrete cortical areas
• Hierarchical Organization
-lower tier, higher tier
• Parallel Streams
- what vs. where
- intra-area (blobs vs interblobs)
- retinotopy
• Feedforward and Feedback connections
Extrastriate Cortex
Criteria For a Visual Area
• Cyto-, myeloarchitecture
• Connectivity
• Retinotopy
-complete or partial map of visual space
-represent a point in space only once?
-smoothly varying?
-orthogonal axes?
• Specialized Function
• Topography
New Way to Gain a
Clear View of the Brain
New York Times
October 10, 2011
Monkey Visual Cortex
Doctrine of the Receptive Field
Retinotopy
V2
V3
V1
Multiple “areas” V1, V2, V3
Receptive Fields at V1/V2 Border
V2
V1
1
8
16
9 10 11 12 13 14 15 16
8 7 6 5 4 3 2 1
V2
Functional Division of Labor?
(motion)
(color)
“What” versus “Where” Pathways
Original concept came from lesion studies in monkeys
(Mishkin & Ungerleider, 1982)
“What” versus “Where” Pathways
Cross talk remains, and feedback is prevalent
Extrastriate Visual Areas
thin- col - V4
inter- ori -V4
thick - ori dis - MT
• V3d and V3A
• MT - MST
• LIP - 7a
also magno-like
magno input, V1 4B, thick, dir, dis, motion, depth
Optic flow input, large RF, multimodal, project to frontal
• V4
Central field input V1, V2, col ori, form primitives
• IT
input V2, V4, object features, face cells, project to multimodal
Very large RF, object invariance, color constancy, training effects
MT
* Strongly associated with motion perception
Lesion and microstimulation studies in monkeys
(Newsome and Pare, 1988; Salzman, Britten, Newsome, 1990)
Wiring Diagram of Visual Areas
“Subway Map From Hell”
Van Essen et al., 1991
Human Visual Cortex
MonkeyVisual Cortex
Adlers, 2011
Human
Lesion-Behavioral Correlations
Localization of Function in Humans
Sources of information
• Focal lesions
• Histological Analysis
• Hemispherectomy
• Commissurotomy
• Unilateral sodium amytal injection
• Brain stimulation
• Spontaneous and evoked electrical potentials
• Functional brain imaging
Retinotopic Areas
• Mapping Visual V1 with Clinical Stimulation
(Dobelle et al, 1979)
• Mapping Visual Areas Via Callosal Projections
(Clark & Miklossy, 1990)
• Mapping Visual V1 via Lesion-Scotoma Correlations
(Horton & Hoyt, 1991)
“state-of the-art” update of Gordon Holmes’Maps (1918)
Human V1, V2, V3, V3A, V6, VP, V4, V8
Syndromes From Isolated Case Studies
Akinetopsia
Human MT
Zihl et al., 1983
Syndromes From Isolated Case Studies
Achromotopsia
c color constancy
o
l
o
r
Human V4/V8
c
Visual Agnosia
Aperceptive Agnosia - thought to be due to a disability in the construction
of a stable representation of visual form, which impairs all high order recognition.
Associative Agnosia - thought to reflect a deficit in accessing semantic
(associative) knowledge about an object following the derivation of an intact
perceptual representation of visual form.
“Perception somehow striped of its meaning” (Teuber)
Example: The man who mistook his wife for a hat (Oliver Sacks, 1985)
Syndromes From Isolated Case Studies
Prosopagnosia
Syndromes From Isolated Case Studies
Prosopagnosia
Benton
Facial
Recognition
Test
Neurons Selective For Faces in Monkey IT
Human Face Areas
anterior
• fMRI studies with humans
show increased activity in
the fusiform face area (FFA).
Inverted faces are hard to recognize.
We are all face “experts”
inflated brain
inferior view
Spatial Neglect
Artist’s rendition of spatial neglect
German artist Anton Raderscheidt showed graduated recovery over eight-month period.
Drawings of Patients with Spatial Neglect
Example Lesions that Produce Neglect
Modern Analysis of Lesion Overlap
Right Hemisphere