Vision 2 Flashcards
How did hubel and wiesel demonstrate the prescence of orientation columns?
From the careful study of how optimum orientations of cells change in electrode penetrations done at different angles
Showed that The medial track (left) is only slightly oblique: optimum orientations
change only slightly.
The lateral track (right) is markedly oblique: optimum orientations
change markedly
What conclusion did hubel and wiesel come to?
cells tuned to similar orientations are
arranged in columns perpendicular to the cortical surface
What are binocular cells in the primary visual cortex
A neuron in the visual cortex that receives inputs from both eyes.
What type of responses can binocular cells show?
- Shows responses of 3 cells (marked 1,2 & 3) – each cell having a
different spike signature - Cells 1 and 2 respond for either eye (and equally), but show
better response for simultaneous stimulation of both eyes. - Cell 3 responds only for binocular stimuli
What did hubel and wiesel find out about ocular dominance in the cortex?
Again in recordings of single cell responses in separate electrode penetrations,
Hubel & Wiesel found that in penetrations perendicular to the cortical surface,
most cells had similar ocular dominance, either driven largely by the left eye or
the right eye.
ways of determining functional architecture?
A. Neuroanatomical tracing techniques
* Radioactive amino acids
– Inject into one eye and determine labelling in cortex (TERMINAL
ARBOURS)
* 2-Deoxyglucose (2DG)
* Glucose analog taken up (after visual stimulation) but not metabolized
(ACTIVE REGIONS )
* Cytochrome oxidase
* Mitochondrial enzyme (HIGH BASAL METABOLIC RATE - layer 4 and
blobs)
B. Optical Imaging
* Voltage-sensitive dyes, intrinsic signals, 2-photon imaging
Large scale determination of functional architecture
C. Optogenetics
* Using light to control cells made to express light-sensitive ion channels,
with use of genetically modified strains or viral vectors.
How can you demonstrate orientation columns using a technique?
Using deoxy-glucose autoradiography. Injected. Visual fields stimulated using 1 orientation. Cells that are more active in response will show up as taking in more glucose
How can you demosntrate ocular dominace columns?
Through injecting radioactive amino acid proline and autoradiographing.
How would you identify highly metabolic areas? Esp cells that have been active for a long time?
Using cytochrome oxidase. Identifies areas of high metabolism as it is involved in KREBS.
What does staining with cytochrome oxidase show in v1 and v2?
Blobs inn V1 and stripesin V2.
what is the Relationship of cytochrome oxidase blobs to the
ocular dominance columns?
Relationship of cytochrome oxidase blobs to the
ocular dominance columns revealed using radioactive
proline injection into the eye
Cytochrome oxidase blobs coincide with centres of ocular
dominance columns
How can you tell where left eye afferents termiante? Ocular domiance of left eye?
** histology is
performed, showing
autoradiographic label
**transported **to the left eye
layers of the LGN (above) and
trans-synapticaly to the
termination zones of the
geniculate afferents in V1
corresponding to the injected
(left) eye.
Optical Imaging of intrinsic signals from visual cortex
The sources of activity dependent changes
Used to use voltage sensitive dye. This is harmful
Can use normal natural signals.
(1) Blood volume changes (2) Changes in oxygenation of blood - in
deoxyhaemoglobin and oxyhaemoglobin (3) light scattering changes
from ion and water movement
Optical imaging to identify ocular dominance?
Stimulate one eyes close the other. Camera focused about 800 microns below surface. Dark areas show active regions corresponding to the eye that was exposed to visual stimuli
Ocular dominance domains on visual cortex
Optical imaging to identify orientation columns.
Open eyes. Present 1 orientation. Activity recorded . From the maps of activity constructed for each of 8 different orientations
(presented binocularly), the computer programme builds up the map of
orientation domains in pseudocolour.
