11. Visual Pathways (Black)

agnosia (loss of memory of an object by sight) results from a lesion to what area?

"what" (parvocellular) stream, responsible for object recognition

activity in primary visual association areas depends on _____ while in visual association areas it depends on _____.

*light* (response is the same for normal vs. scrambled image as long as quantity of light is the same) *form* (more active when there is a known object to identify vs. a scrambled image)

blood supply of: optic nerve, retina, lateral geniculate nucleus (LGN), optic chiasm + optic tract, optical radiations, striate cortex?

*nerve*: ophthalmic artery (branch of internal carotid) *retina*: central retinal + posterior ciliary arteries (branches of ophthalmic a.) *LGN*: posterior cerebral a. *chiasm + tract*: from multiple neighboring arteries (ACA, MCA, + posterior communicating artery) *radiations*: MCA *striate*: PCA (some overlap w/ MCA)

what nuclei/areas in the cortex are responsible for: 1. conscious awareness of what you are seeing 2. pupillary light reflex

1. lateral geniculate nucleus 2. pretectal area

retrolenticular or sublenticular fibers: -superior retina (lower visual quadrant), contralateral visual field -inferior retina (upper visual quadrant)

1. retrolenticular 2. sublenticular

overview: visual fields what fibers cross?

B & C = binocular fields A & D = monocular fields nasal retina fibers cross, temporal retina fibers stay ipsilateral

Case: right homonymous hemianopsia (absence of visual field on the R side) How would the pupillary light reflex be affected?

B (I think?? <-- confirm with someone)

what areas of the brain are visual cortex areas? visual association areas?

V1 = visual cortex (either side of calarine sulus) VA (V2-V5) = visual association areas (more of occipital lobe) (remember: S1 = primary somatosensory cortex SA = somatosensory association areas, "where" pathway SII = secondary somatosensory cortex, "what" pathway)

pupillary light reflex: direct vs. indirect rxn? pathway?

direct: response in ipsilateral eye indirect: response in contralateral eye pathway: rods/cones --> (retinal ganglion cells via optic tract) --> prectecal area --> (CN 3) --> pupillary constrictor muscle

Self-study: which vision field lesions would cause these deficits?

image

overview: course of optic radiations focusing on an object in upper + lower R visual fields

image

what are optic radiations?

large bundle of fibers that originate in the lenticulate nuc + course through parietal (retrolenticular fibers) or temporal lobe (sublenticular fibers, Meyer's loop) note: in image, green circle = lenticular nuc

Case: right homonymous hemianopsia (absence of visual field on the R side) Where is the lesion?

left LGN, left visual cortex

T/F: The "what" and "where" streams of information remain separate from the retina to the primary visual cortex & beyond.

note: know visual association areas as a collective group (don't need to know difference btwn V2 & V4)

location of primary visual cortex

occipital lobe, portions of the cuneus (C) + lingual (L) gyri that border the *calcarine sulcus*

visual pathway (general)

optic nerves --> optic chaism --> optic tract --> lateral geniculate nucleus --> visual cortex in occipital lobe

define: striate cortex

same as visual cortex (walls of calcarine sulus in occipital lobe)

where are the pathways of: -"where" (magnocellular) stream of visual information -"what" (parvocellular) stream of visual information

where = location in space & movement, dorsal pathway to posterior parietal lobe what = color, form (object identification), ventral pathway to inferior aspect of temporal lobe