Extrastriate Cortex and Higher Cortical Deficits Adlers Physiology

Extrastriate Cortex and Higher Cortical Deficits Adler’s Physiology of the Eye 11 th Ed. Chapter 31 - by Boyd & Matsubara http: //www. mcgill. ca/mvr/resident/

Multiple Visual Areas Beyond V 1 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 V 2 V 3 V 1 Multiple “areas” V 1, V 2, V 3

Receptive Fields at V 1/V 2 Border V 2 V 1 1 8 16 9 10 11 12 13 14 15 16 8 7 6 5 4 3 2 1

V 2

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 - V 4 inter- ori -V 4 thick - ori dis - MT • V 3 d and V 3 A • MT - MST • LIP - 7 a also magno-like magno input, V 1 4 B, thick, dir, dis, motion, depth Optic flow input, large RF, multimodal, project to frontal • V 4 Central field input V 1, V 2, col ori, form primitives • IT input V 2, V 4, 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 Monkey. Visual 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 V 1 with Clinical Stimulation (Dobelle et al, 1979) • Mapping Visual Areas Via Callosal Projections (Clark & Miklossy, 1990) • Mapping Visual V 1 via Lesion-Scotoma Correlations (Horton & Hoyt, 1991) “state-of the-art” update of Gordon Holmes’Maps (1918) Human V 1, V 2, V 3 A, V 6, VP, V 4, V 8

Syndromes From Isolated Case Studies Akinetopsia Human MT Zihl et al. , 1983

Syndromes From Isolated Case Studies Achromotopsia ccolor constancy o l o r Human V 4/V 8

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 • f. MRI 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