Extrastriate Cortex andHigher 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

• Discrete cortical areas

• Hierarchical Organization-lower tier, higher tier

• Parallel Streams- what vs. where- intra-area (blobs vs interblobs)- retinotopy

Extrastriate Cortex

• Feedforward and Feedback connections

• Cyto-, myeloarchitecture

• Connectivity

• Retinotopy

• Specialized Function

• Topography

-smoothly varying?-orthogonal axes?

-represent a point in space only once?-complete or partial map of visual space

Criteria For a Visual Area

New Way to Gain a Clear View of the BrainNew York Times October 10, 2011

Extrastriate Cortex

Monkey Visual Cortex

Retinotopy

V1

V2V3

Multiple “areas” V1, V2, V3

Doctrine of the Receptive Field

18

16

9 10 11 12 13 14 15 16

7 6 5 4 3 2 18

Receptive Fields at V1/V2 Border

V1 V2

V2

Functional Division of Labor?

(color)

(motion)

“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

• MT - MST

• V3d and V3A

• LIP - 7a

• V4• IT

thin- hcol - V4inter-h ori -V4thick - hori hdis - MT

magno input, V1 4B, thick, hdir, hdis, motion, depth

also magno-like

Optic flow input, large RF, multimodal, project to frontal

Central field input V1, V2, hcol hori, form primitives

input V2, V4, object features, face cells, project to multimodalVery 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)

“Subway Map From Hell”

Wiring Diagram of Visual Areas

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

• Mapping Visual V1 via Lesion-Scotoma Correlations(Horton & Hoyt, 1991)

• Mapping Visual V1 with Clinical Stimulation(Dobelle et al, 1979)

• Mapping Visual Areas Via Callosal Projections(Clark & Miklossy, 1990)

Retinotopic Areas

Human V1, V2, V3, V3A, V6, VP, V4, V8

“state-of the-art” update of Gordon Holmes’Maps (1918)

Akinetopsia

Syndromes From Isolated Case Studies

Zihl et al., 1983

Human MT

Achromotopsia

Syndromes From Isolated Case Studies

Human V4/V8

color co

color constancy

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)

Prosopagnosia

Syndromes From Isolated Case Studies

Prosopagnosia

Syndromes From Isolated Case Studies

BentonFacialRecognitionTest

Neurons Selective For Faces in Monkey IT

Human Face Areas

• fMRI studies with humans show increased activity in the fusiform face area (FFA).

anterior

inflated braininferior view

Inverted faces are hard to recognize.

We are all face “experts”

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