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Home , Chiasm (anatomy), Optic chiasm, Optic nerve, Optic tract, Visual cortex

VISUAL PATHWAYS

Valentin Dragoi

Department of Neurobiology and Parallel streams of Outline

• Visual pathways: From to the

• Information ppgrocessing in Outline

• Visual pathways: From retina to the cortex

• Information ppgrocessing in visual cortex VISUAL PATHWAY

Retinal ggganglion cell leave the at the

The retinal axons exit the eye to form the optic . VISUAL PATHWAY Consists of 3° afferent axons Axons of retinal ganglion cells

OPTIC Optifibiiific nerve fibers originating from the nasal retina that decussate in the Optic nerve fibers originating from the temporal retina do not decussate in the optic chiasm

OPTIC TRACT Consists of 3° afferent axons from the nasal half of the contralateral eye & the temporal half of the ipsilateral eye AXONS:

Optic Optic nerve tract

Optic : chiasm regulation of cidihthircadian rhythms

Lateral geniculate Pretectum: reflex contlftrol of pupil and lens

Optic radiation

Superior colliculus: orienting the movements of head and Striate cortex LATERAL GENICULATE NUCLEUS OF THE

The thalamic nucleus

LGN MGN

LGN organized into 6 cell layers 2 Magnocellular layers 4 Parvocellular layers with thin layers of kinocellular (dust-like) interposed All LGN neurons • are monocular - respond to stimulation of one eye only • have concentric (ON/OFF or OFF/ON) receptive fields Type mLGN neurons in LGN magnocellular layers • synapse with Type M retinal ganglion axons • have large concentric receptive fields • are insensitive to • sensitive to small changes in brightness levels (scotopic vision) • are rapidly-adapting (motion sensitive) Type pLGN neurons in LGN parvocellular layers • synapse with Type P retinal ganglion axons • have small concentric recepti ve fields ( high acuity ) • are sensitive to color (color sensitivity) • are not sensitive to small changes in brightness levels • are slowly-adapting (indicate the duration is “on”) Outline

• Visual pathways: From retina to the cortex

• Information ppgrocessing in visual cortex PRIMARY VISUAL CORTEX

Primary visual cortex

Calcarine fissure is differentiated into 6 horizontal layers COLOR SELECTIVITY

SPECIALIZED PROCESSING :

CHARACTERISTICS OF V1 BLOB (COLOR ) CELLS •coliilor sensitive - target ofkf kLGN axons • small concentric receptive fields • monocular - onlyyy one eye stimulates the blob cells • indifferent to stimulus orientation • indifferent to stimulus movement (slowly-adapting)

BLOBS RETINA …. ….

Striate cortex: V1

V1 BLOB CELL RESPONSES Orientation selectivity

Stimulus Stimulus orientation presented Light b ar sti mul us projected on screen Recording from visual cortex Record

01 23 Time (sec) ORIENTATION SELECTIVITY

SPECIALIZED PROCESSING : COMMON CHARACTERISTICS OF INTERBLOB CELLS

•eldifildlongated receptive fields • insensitive to color • binocular w/ ocular dominance > one eye elicits a stronger response • most are sensitive to stimulus orientation > strongest response to particular orientation …. ….

Interblob cells ORIENTATION SELECTIVITY

SPECIALIZED PROCESSING :

SHAPE/FORM & LOCATION V1 INTERBLOB CELLS •eldifildlongated receptive fields • insensitive to color • binocular w/ ocular dominance > one eye elicits a stronger response • sensitive to stimulus orientation > strongest response to particular orientation

•insensitive to movement - target of pLGN axons > slowly-adapting response • location specific > stronggpest response in field center DIRECTION OF MOTION

SPECIALIZED PROCESSING :

MOTION SENSITIVE V1 INTERBLOB CELLS •eldifildlongated receptive fields • insensitive to color • binocular w/ ocular dominance > one eye elicits a stronger response • sensitive to stimulus orientation > strongest response to particular orientation • sensitive to MOVEMENT => target of mLGN axons DIRECTION OF MOTION

SPECIALIZED PROCESSING :

MOTION+LOCATION SENSITIVE V1 INTERBLOB CELLS •eldifildlongated receptive fields • insensitive to color • binocular w/ ocular dominance > one eye elicits a stronger response • sensitive to stimulus orientation > strongest response to particular orientation • most sensitive to motion => target of mLGN axons •some location specific DIRECTION OF MOTION

SPECIALIZED PROCESSING :

MOTION DIRECTION SENSITIVE V1 INTERBLOB CELLS •eldifildlongated receptive fields • insensitive to color • binocular w/ ocular dominance > one eye elicits a stronger response • sensitive to stimulus orientation > strongest response to particular orientation • most sensitive to motion - => target of mLGN axons

•others direction specific ‘Ice-cube’ model of primary visual cortex

R L R L R L R L Optical imaging of mputer imulus

functional domains oo St c

Cortical vasculature Amplifier Camera deo data quisition ii cc

Light guide V a

Single condition maps Orientation map EXTRA-STRIATE AND ASSOCIATION AREAS

NON- PRIMATES VISUAL CORTICAL AREAS

Posterior

Middle & Medial Superior Temporal

Striate (Visual) cortex

Extrastriate cortex

Inferior temporal gyrus HIGHER ORDER PROCESSING

V1 SENDS MOST OF ITS AXONS TO

EXTRASTRIATE CORTEX (V2, V3 & V4) SEND AXONS TO ASSOCIATION CORTEX (TEMPORAL & PARIETAL AREAS)

DORSAL STREAM: > SUPERIOR TEMPORAL & PARIETAL

NECESSARY FOR •spatial orientation • binocular fusion • depth • spatial location • movement detection

“THE WHERE” HIGHER ORDER PROCESSING

V1 SENDS MOST OF ITS AXONS TO EXTRASTRIATE CORTEX

EXTRASTRIATE CORTEX (V2, V3 & V4) SEND AXONS TO ASSOCIATION CORTEX (TEMPORAL & PARIETAL AREAS)

VENTRAL STREAM: > INFERIOR “TEMPORAL” GYRUS

IMPORTANT FOR SHAPE & COLOR • perception • discrimination • recognition • memory • learning

“THE WHAT” Motion processing Shape processing in infero-temporal (IT) cortex Parallel streams of visual processing

Spatial vision Lesion to MT abolishes the perception of motion X without affecting object Object vision vision

X Lesion to V4 abolishes without affecting spatial vision Suggested readings

1. book (Purves et al.), Chapter 12