l 22: ganglion cell receptive fields

Question 1

how many types of bipolar cells in primate retina

Answer 1

around 12 types: each type collects info from photoreceptor and sends to distinct layer, can group into on or off bipolar cells
on = brightening
off = darkening

Question 2

how many types of amacrine cells are in the retina

Answer 2

35+ 
most diverse class of cells, each has on morphology and stratification

Question 3

pathways in the retina

Answer 3

parallel pathways in retina extract different image features
- record from different ganglion cell and see each type gives slightly different representation
some take high/low spatial frequencies or light/dark features

Question 4

retinal mosaics

Answer 4

tiling pattern for 1 type of ganglion cell:

want to distribute features through whole visual field so need arrays of ganglion cells dispersed through retina

Question 5

mapping receptive fields

Answer 5

move spot of light- electrode inserted into optic nerve, recod AP when stimuli presented in specific space
- center shows most activity

Question 6

on and off center retinal ganglion cells

Answer 6

off cell spikes most during darkening

on cell soikes most during brightening

Question 7

mach bands

Answer 7

centre surround in eye
B appears brighter (at an edge) because surround center highlights edge and sharpens features
- always want to pay attention to changes in environment

Question 8

cellular basis for lateral inhibition

Answer 8

2 layers: inner and outer, both inhibitory and both extend laterally
horizontal cells (outer layer) depolarized in dark, cant fire AP because tonic depolarized so Na inactivates
amacrine cells (inner layer) hyperpolarized at resting so can support AP

Question 9

surround inhibition in voltage clamp

Answer 9

clamped at -60: represent glutamate currents
small spot gets weak response, as increase psot size you activate more on center receptors
reach end of receptive field and should plateau- but instead see smaller response because lateral inhibition crosses out bipolar cells

Question 10

role of GABA in surround inhibition

Answer 10

added GABA blocker picrotoxin which showed no inhibition
therefore gaba must be mediating lateral response
either horizontal or amacrine are GABAergic

Question 11

spike activity for surround inhibition

Answer 11

put TTX to block Na channels which are in amacrine cells but not horizontal cells
- action potentials are requried for mediating surround which shows inhibition must come from spiking neuron which is amacrine not horizontal

Question 12

direct inhibition vHold at 0

Answer 12

amacrine cell fires AP that mediates inhibition could either come to bipolar cell or onto ganglion cell
hold at 0mV to measure inhibition (GABA)