feedback pathways to V1 carry mainly excitatory input and porject preferentially to pyramidal cells
- V1 is characterized by a unique layered appearance in Nissl stained tissye = striated
magnocellular pathway: associated w/ movement of the visual image, to upper parts of the layer 4B
parvocellular pathway: associated w/ form and color, to lower parts of layer 4
- M-cells from 4C project to layer 4B and have side projections to interblob cells and now you know how B responds to input from both sides (not just contralateral or ipsilateral)
- P-cells from 4C project to more superficial layers in 2 and 3 where you see ocular dominance columns cell can respond to either eye
- critical dev. period (12wks) req’d to set up ocular dominance columns, for high acuity, depth perception
- past a certain age, wiring becomes hard-wired, a lot less plasticity
- ex: lazy-eye, patch good eye to allow the bad eye develop
- visual deprivation experiments in cats, suture eyes and study ODCs, suturing causes loss of striation patterns
- neurons in primary visual cortex respond preferentially to oriented edges (all edge orientations equally represented in visual cortex)
- different orientations of a bar on a screen and recording from layer 2/3 of V1 of a specific neuron, up and down = max burst, can graph a tuning curve and see which stimulus responded it best to
- a given orientation in a visual scene seems to be encoded by the activity of a distinct population of orientation-selective neurons
- respond to same stimulus in the same position in the VF if recording up and down (“a column”) in the V1
- similar RFs, and orientation selectivity is similar
- BUT, if you go across (R to L of the cortex), they have different RFs and different responses to different orientations of the bar as you go across
- “orderly progression of RFs and orientation selectivity”
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