VISUAL PATHWAYSVISUAL PATHWAYS
Valentin Dragoi
Department of Neurobiology and Anatomy
Parallel streams of visual processing
Outline
• Visual pathways: From retina to the cortex
• Information processing in visual cortexp g
Outline
• Visual pathways: From retina to the cortex
• Information processing in visual cortexp g
VISUAL PATHWAY
Retinal ganglion cell axonsg gleave the eye at the optic disc
The retinal ganglion axons exit the eye to form the optic nerve.
OPTIC NERVEVISUAL PATHWAY
Consists of 3° afferent axonsAxons of retinal ganglion cells
OPTIC CHIASMi fib i i i fOptic nerve fibers originating from
the nasal retina that decussate in the optic chiasmp
Optic nerve fibers originating fromthe temporal retina do not
decussate in the optic chiasmdecussate in the optic chiasm
OPTIC TRACTConsists of 3° afferent axons from the nasal half of the
contralateral eye & the temporal half of the ipsilateral eye
RETINAL GANGLION CELL AXONS: OPTIC TRACT
Optic nerve
Optic tract
Optic chiasm
Hypothalamus: regulation of
i di h th
Lateral geniculate nucleus
circadian rhythms
Pretectum: reflex t l f il
Optic radiation
control of pupil and lens
radiation
Superior colliculus: orienting the movements of head and eyes
Striate cortex
of head and eyes
LATERAL GENICULATE NUCLEUS OF THE THALAMUS
LGN
The visual system thalamic nucleus
LGNMGN
LGN organized into 6 cell layersLGN organized into 6 cell layers2 Magnocellular layers4 Parvocellular layers
with thin layers of kinocellularwith thin layers of kinocellular(dust-like) neurons interposed
All LGN neurons • are monocular - respond to stimulation of one eye only
Type mLGN neurons in LGN magnocellular layers
• have concentric (ON/OFF or OFF/ON) receptive fields
• synapse with Type M retinal ganglion axons• have large concentric receptive fields• are insensitive to colorare insensitive to color• 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• ha e small concentric recepti e fields (high acuity)• have small concentric receptive fields (high acuity)• are sensitive to color (color sensitivity)• are not sensitive to small changes in brightness levels• are slowly-adapting (indicate the duration stimulus is “on”)
Outline
• Visual pathways: From retina to the cortex
• Information processing in visual cortexp g
PRIMARY VISUAL CORTEX
Primary visual cortexcortex
Calcarine fissure
Cerebral cortex is differentiated into 6 horizontal layers
COLOR SELECTIVITY
SPECIALIZED PROCESSING
l i i f k
SPECIALIZED PROCESSING: CHARACTERISTICS OF V1 BLOB (COLOR ) CELLS
• color sensitive - target of kLGN axons• small concentric receptive fields• monocular - only one eye stimulates the blob cellsy y• indifferent to stimulus orientation• indifferent to stimulus movement (slowly-adapting)
RETINA
….
….
BLOBS
Striate cortex: V1
V1 BLOB CELL RESPONSES
Orientation selectivity
Li ht b ti l
Stimulusorientation
Stimuluspresented
Light bar stimulus projected on screen Recording from
visual cortexRecordRecord
0 1 2 3Time (sec)
ORIENTATION SELECTIVITY
SPECIALIZED PROCESSINGSPECIALIZED PROCESSING: COMMON CHARACTERISTICS OF INTERBLOB CELLS
l d i fi ld• elongated 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> strongest response to particular orientation
….
….
Interblob cells
ORIENTATION SELECTIVITY
SPECIALIZED PROCESSINGSPECIALIZED PROCESSING: SHAPE/FORM & LOCATION V1 INTERBLOB CELLS
l d i fi ld• elongated 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
> strongest response to particular orientation
> slowly-adapting response• location specific
> strongest response in field centerg p
DIRECTION OF MOTION
SPECIALIZED PROCESSINGSPECIALIZED PROCESSING: MOTION SENSITIVE V1 INTERBLOB CELLS
l d i fi ld• elongated 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
> strongest response to particular orientation
=> target of mLGN axons
DIRECTION OF MOTION
SPECIALIZED PROCESSINGSPECIALIZED PROCESSING: MOTION+LOCATION SENSITIVE V1 INTERBLOB CELLS
l d i fi ld• elongated 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
> strongest response to particular orientation
=> target of mLGN axons• some location specific
DIRECTION OF MOTION
SPECIALIZED PROCESSINGSPECIALIZED PROCESSING: MOTION DIRECTION SENSITIVE V1 INTERBLOB CELLS
l d i fi ld• elongated receptive fields• insensitive to color• binocular w/ ocular dominance
> one eye elicits a stronger response• sensitive to stimulus orientation
> strongest response to particular orientation> strongest response to particular orientation
• most sensitive to motion -=> target of mLGN axons=> target of mLGN axons
• others direction specific
‘Ice-cube’ model of primary visual cortex
R
LRLR
LRLR
L
L
Optical imaging of functional domains im
ulus
ompu
ter
functional domains
Cortical vasculature
St co
Cam
era
ideo
dat
acq
uisi
tion
Amplifier
Vi
acLight guide
Single condition maps Orientation map
EXTRA-STRIATE AND ASSOCIATION AREAS
NON-HUMAN PRIMATES
VISUAL CORTICAL AREASPosterior parietal lobe
Middle & Medial Superior Temporal gyrus
Striate (Visual) cortex
Extrastriate cortex
Inferior temporal gyrus
HIGHER ORDER PROCESSINGV SENDS MOST OF ITS AXONS TO EXTRASTRIATE CORTEXV1 SENDS MOST OF ITS AXONS TO EXTRASTRIATE CORTEX
EXTRASTRIATE CORTEX (V2, V3 & V4) SEND AXONS TOASSOCIATION CORTEX (TEMPORAL & PARIETAL AREAS)ASSOCIATION CORTEX (TEMPORAL & PARIETAL AREAS)
DORSAL STREAM: > SUPERIOR TEMPORAL & PARIETAL
NECESSARY FOR• spatial orientationp• binocular fusion• depth perception • spatial location
“THE WHERE”
• spatial location• movement detection
“THE WHERE”
HIGHER ORDER PROCESSINGV SENDS MOST OF ITS AXONS TO EXTRASTRIATE CORTEXV1 SENDS MOST OF ITS AXONS TO EXTRASTRIATE CORTEX
EXTRASTRIATE CORTEX (V2, V3 & V4) SEND AXONS TOASSOCIATION CORTEX (TEMPORAL & PARIETAL AREAS)
VENTRAL STREAM: > INFERIOR “TEMPORAL” GYRUS
ASSOCIATION CORTEX (TEMPORAL & PARIETAL AREAS)
IMPORTANT FORSHAPE & COLOR
i• perception• discrimination• recognition g• 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
Object vision
XLesion to MT abolishes the perception of motion without affecting object vision
XLesion to V4 abolishesLesion to V4 abolishes color vision without affecting spatial vision
Suggested readingsSuggested readings
1. Neuroscience book (Purves et al.), Chapter 12