Brain and Vision

Purves et al., Chapter 12 (and bits of Chapters 11 and 24)

Projection to Brain

Fig. 12.1 p. 258
Overall Visual Projection
Eye -> LGN (Lateral geniculate nucleus, genu= knee, part of thalamus) -> striate cortex
Temporal retinal field = nasal visual field stays ipsilateral at chiasm
Nasal retinal field = temporal visual field crosses to contralateral side at chiasm
From LGN to striate cortex = area 17 = V1
Retinotopy (like somatotopic organization) is preserved
*Eye -> pretectum - pupil size (iris) and control of lens (accomodation)
Eye -> superior colliculus - eye and head movements (Chap. 19)
Eye -> hypothalamus - to regulate circadian rhythms (see, in chapter 27)

*Fig. 12.2 p. 259
pupillary reflex
Pretectum -> Edinger-Westphal nucleus -> cranial nerve III->ciliary ganglion ->parasympathetic fiber.
Note connection to both ipsilateral and contralateral sides after pretectum, so pupillary reflex should be bilateral.
Kids, go ahead and try this.
Important test in neurology.

Fig. 12.13 A & B p. 268
Thalamus
Cells have center - surround receptive fields like ganglion cells
1, 4, 6 contralateral -- thus 2, 3, 5 ipsilateral

Fig. 12.15A p. 269
large and small retinal ganglion cells
Magnocellular - large receptive fields for processing movement - connect to LGN 1 & 2
Parvocellular cells connect to layers 3, 4, 5, & 6 and process color, also for acuity

Cortical processing

Landmark papers

DHHubel & TNWiesel, Receptive fields, binocular interaction and functional architecture in the cat's visual cortex, JPhysio, 160, 106-154, 1962
TNWiesel, DHHubel & DMKLam, Autoradiographic demonstration of ocular dominance columns in the monkey striate cortex by means of transneuronal transport, Brain Res 79, 273-279, 1974 (see also J NIH Res, 5, 61-67, 1993)
DHHubel & TNWiesel, Brain mechanisms of vision, Scientific American September 1979 (vol 241, #3), pp 150-162.

Tom Yin's home page, follow links, Simple cell is a good video to show how work was done

Fig. 12.8 A & B p. 264
cat (monkey) looks at screen, cell responds best to line at angle
Striate cortex - physiology and anatomy
Hubel & Wiesel share 1981 Nobel for "information processing in the visual sytem"

Fig. 12.11 p. 266
there are vertical columns of preferred angle (just like in somatosensory system)
presumably, to prefer line at angle, cell receives inputs from from alligned center surround cells
these are called simple cells
complex cell - line at algle moving in direction
hypercomplex cells - line has end - corner
vertical electrode penetration gives cells with all the same preferred angle
an oblique penetration tracks different angles
Note that there are 6 layers of cells, IV has inputs from LGN

"Philosophical question" -- does processing get to more and more levels of complexity until you find "grandmother cells" which recognize, specifically, your grandmother's face?

Fig. (like 12.13 B & C) p. 268
experiment to determine ocular dominance columns (0.5 mm wide)
There are cortical cells with input from one eye, from the other eye, and, in between, from both eyes.
Binocularly driven cells should be necessary for stereopsis, the kind of depth perception which relies on the focussing of both eyes.

Fig. 12.14 p. 269
Apparently, cells can preferentially respond to disparity from fixation
depth-perception
stereopsis

Even higher order visual processing

With all that color processing in the LGN, it seemed odd how far the work on the cortex got without any mention of color

Fig. 12.16A 272
V4 - color but not movement
MT (middle temporal) - direction of movement but not color

Fig. 12.18 p. 274
parietal stream - spatial vision
temporal stream - object recognition

This relates to Andrew Laguna S.J.'s presentation on the binding problem (pdf) (PodCast)

Development of visual connections

Fig. 24.4 p. 545
If a radioactive amino acid is injected into one eye, labeled proteins cross synapses at LGN and mark ocular dominance columns in cortex; this is detected by microscopic autoradiography.
Binocular cells connect up correctly at first

Fig. 24.5 p. 546
Then there is a sensitive (critical) period in the first few months of life during which patterned visual input from both eyes is necessary to maintain binocular input to cortical cells.
Thus early visual defects like cataract or strabismus (cross-eyes or lazy eye) need to be corrected right away.

Here are autoradiographs. A of normal visual cortex, nd B after monocular deprivation from 2 weeks to 18 months in monkey

Recent Literature

*P Sinha Once blind and now they see, July 2013, 48-55. Blind from birth Indian children get surgery, takes a while to learn to see. Hard to put things together. SK was 29, had congenital aphakia (rare). "not particularly thrilled" Motion helped

*BPeak Seeing is feeling (letter to the editor) Nov p 6. Book ­p; Pilgrim at tinker creek (1974 by Annie Dillard) she quotes  Space and Sight (1932), patient could name a cube by feeling it but, after cataract surgery could not name it if (s)he saw it

Exam questions from 2005 - 2011 relating to this outline

A stroke wipes out the connection of the pretectum to the contralateral Edinger-Westphal nucleus but not to the ipsilateral one. How could you infer this with a very simple non-invasive vision test on a cooperative subject?

There would still be a pupillary reflex but not in the contralateral eye

Say something about how the nasal portion of the retina projects to the lateral geniculate nucleus

nasal retina connects to contralateral LGN's layers 1, 4, and 6.

An electrode is in a simple cell that fires action potentials vigorously when stimulated with a thin, vertical stripe of light. How does it respond to a thick stripe in the same location, and why does it react that way?

a lot less or not at all b/c the thick stripe also stimulates the inhibitory surround

Injection into one eye followed by a specialized histological technique demonstrated a zebra-stripe pattern of ocular dominance columns in the visual cortex. Answer either (1) What was injected in the eye? Or (2) What technique was used for the visualization in the cortex?

a radioactive amino acid, audioradiography

You went home and tried what I suggested, shined a flashlight to one eye. Alas, only one pupil constricts. Tell me a place where you have nerve damage.

has to be after the pretectum. maybe between the pretectum and the Edinger-Westphal nucleus (one of two paths) or from there to the ciliary ganglion, to the muscle (on one side)

If Hubel and Wiesel had looked for a grandmother cell instead of the cells they identified (e.g. simple cell), why wouldn't they have gotten a Nobel Prize?

Their systematic approach was very productive, good thing they didn't start looking for a needle in a haystack

How were the ocular dominance columns in normal and visually deprived animals visualized?

audioradiography, histological slices exposed photographic "film"

Occasionally I pointed to how uninteresting the wall was vs the perceptual richness of the map on the wall. Say something about how the receptive field organization in the lateral geniculate nucleus contributes to this difference.

center surround influences contrast

What is the most obvious thing that happens between the pretectum and the Edinger-Westfall nucleus?

goes bilateral

Concerning layers in the lateral geniculate nucleus, answer either (1) What is the main difference between layers 1, 4, & 6 vs 2, 3, & 5? Or (2) What is the main difference between layers 1 & 2 vs 3 to 6?

1,4,6 contralateral, 1, 2 magnocellular

In the "movie" of Hubel and Wiesel's simple cell experiment, how come a wide line of light projected right on target did not elicit firing while a thin line, also accurately aimed, did?

wide hit inhibitory surround also

An oblique electrode track traverses several millimeters of the visual cortex. What change do you notice about the receptive field properties of the firing neurons you encounter?

one eye -> both -> other, (also angle of line)

A radioactive amino acid was injected into one eye. Say one of the several cell biological events that must occur to give an autoradiogram of ocular dominance columns. (I am not asking how to do autoradiography.)

is put into protein, is transported down axon, is transported across synapse, transported down other axon

Why did I tell the story of geese following the Nobel prize winning ethologist Konrad Lorenz in the context of the visual cortex?

sensitive (critical) period

How would you test whether a patient's contralateral connection from the pretectum to the Edinger-Westphal nucleus were disrupted?

light to one eye would not consstrict the contralateral pupil

Specifically, what crossed the LGN (lateral geniculate nucleus) synaptic cleft to allow Hubel to see the ocular dominance columns using autoradiography?

3H labeled protein

Where do the axons of the the temporal retina (nasal visual field) go at the chiasm?

to ipsilateral LGN

What is the word for the special type of "depth perception" mediated by the parallax from focussing both eyes (and neural interactions of binocular cells)?

stereopsis

If a child were born with a congenital cataract in one eye, why should this deserve immediate attention?

brain connections from that eye would vanish without patterened vision

Light stimulation to one eye activates that eye's optic nerve. By what mechanism would there be efferent output to the iris from both occulomotor nerves?

connection to one pretuctum goes bilaterally to Edinger-Westphal nuclei

The inputs from the two eyes to the lateral geniculate nucleus do not mix. In what manner are they kept separate?

they go to different layers, contralateral to 1, 4, & 6, ipsilateral to 2, 3, & 5

A thin bar of light made the simple cell fire quickly. Why did a wider bar not do likewise?

Because the wider bar also hit the inhibitory areas in the receptive field of that cell

What technique did Hubel and Wiesel use to get that picture of the visual cortex with stripes?

Autoradiography, or, inject radioactive amino acid into one eye and observe the protein transported transynaptically from ganglion cell across LGN to cortex

As an electrode is advanced obliquely across columns in the visual cortex, what changes?

One could say preferred eye of input or one could say preferred angle of line

Why did Hubel and Wiesel feed their microelectrode amplifier into a loud speaker?

easy to judge firing rate by the sound

Why did a wide line centered on the simple cell's receptive field elicit less of a response than a narrow line?

even though it stimulates the excitatory receptive field, it also stimulates the surrounding inhibitory ones

While an electrode is advanced obliquely through the cat's visual cortex, first the left eye predominates, then the right eye. What else has been changing during that advancement?

preferred angle

When is the critical (sensitive) period for development of binocular connections in the cat visual cortex?

birth to 2 & 1/2 mo

When autoradiography was used to demonstrate ocular dominance columns, how did the film (photographic emulsion) get exposed?

radioactivity (in cortex protein) exposed film in the dark



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