Slide 1The visual system pathwayThe lateral geniculate nucleusThe lateral geniculate nucleusPrimary visual cortexPrimary visual cortexPrimary visual cortexPrimary visual cortexPrimary visual cortexPrimary visual cortexExtrastriate cortexExtrastriate cortexExtrastriate cortexExtrastriate cortexExtrastriate cortexExtrastriate cortexExtrastriate cortexSlide 18THE CENTRAL VISUAL SYSTEMNEUR 3000Dr. Joseph J. NormandinTHE VISUAL SYSTEM PATHWAYTHE LATERAL GENICULATE NUCLEUS•The LGN receives input from ganglion retinal cells•Layers 1, 4, 6 receive input from the eye on the opposite side•Layers 2, 3 5 receive input from the eye on the same side•Two inner layers are magnoceullar•Receive information from M-type ganglion cells •Four outer layers are parvocellular•Receive information from P-type ganglion cells•Between each layer is the koniocellular layer of tiny cells•Receive information from nonM-nonP-type ganglion cellsTHE LATERAL GENICULATE NUCLEUSPRIMARY VISUAL CORTEX•Primary visual cortex (V1 / striate cortex) receives input from the LGN•Cortical cells don’t respond to simple stimuli, like a point of light•A lot of information about lots of points of light in your visual field is combined here•Cortical cells can respond to:•Orientation of a stimulus•Motion of a stimulus•Location of a stimulusPRIMARY VISUAL CORTEXPRIMARY VISUAL CORTEX•Primary visual cortex (V1 / striate cortex) receives input from the LGN•Cortical cells don’t respond to simple stimuli, like a point of light•A lot of information about lots of points of light in your visual field is combined here•Simple cortical cells•Respond to an edge or bar with particular orientation and location•Complex cortical cells•Respond to an edge or bar with particular orientation irrespective of locationPRIMARY VISUAL CORTEXPRIMARY VISUAL CORTEX•When stained to reveal cytochrome oxidase there is a distinct structure to striate cortex•Blobs and Interblobs•Everything we have spoken of so far occurs in neurons of the Interblob regions•The Blob regions do not respond to orientation or motion, but rather to particular wavelengths of light•ColorPRIMARY VISUAL CORTEXEXTRASTRIATE CORTEX•V1 sends projections to other visual cortical areas that are organized into two “streams”•The ventral “what” pathway•Identifies objects•The dorsal “where” pathway•Identifies motionEXTRASTRIATE CORTEX•The ventral “what pathway”•The perception of form: V1V2V3V4IT•Cells in V2 respond to “illusory contours”EXTRASTRIATE CORTEX•The ventral “what pathway”•The perception of form: V1V2V3V4IT•Some cells in V4 respond to complex patterns•Other cells in V4 respond to color•Active when colored stimuli are observed, but not when images are black/whiteEXTRASTRIATE CORTEX•The ventral “what pathway”•The perception of form: V1V2V3V4IT•Inferior temporal cortex (IT) cells respond to complex forms, including forms that the subject has learned to recognizeEXTRASTRIATE CORTEX•The ventral “what pathway”•The perception of form: V1V2V3V4IT•Fusiform gyrus (subdivision of IT) cells respond to faces, including faces that the subject has learned to recognizeEXTRASTRIATE CORTEX•The dorsal “where pathway”•The perception of motion: V1V2V3V5(MT)PP•V5 (MT; medial temporal cortex) neurons respond to moving stimuli•Some cells respond to any movement, some to particular directions•A woman with a lesion to V5 has reported that she sees only static images instead of continuous motionEXTRASTRIATE CORTEX•The dorsal “where pathway”•The perception of motion: V1V2V3V5(MT)PP•Posterior parietal (PP) neurons respond to the location of stimuli•The posterior parietal cortex appears to encode a map of the space around us•Activity in one part of the map corresponds to a stimulus’ location around usANY QUESTIONS?NEUR 3000Dr. Joseph J.