l 25 direction selectivity Flashcards
direction selectivity in the barrel cortex
deflecting whiskers in different directions and make recordings
greatest number occurs at 180 degrees
where do we see direction selectivity
in auditory cortex- upward/downward of speech depending on frequency
somatosensory cortex- move stimulus on hand and see likes C-F direction (area 2 neurons code)
and V1
directionally selective ganglion cells
robust spiking for upwards motion but little spiking for opposite direction
need inputs from 2 sources (photoreceptors) need to be able to compare sensory stimulus and correlate them
need asymmetry or else you get same response
- reichardt detectors
3 types of on DSGC
align with the semicircular canals
important for image stabilization, when head is moving eyes can be stable
dont want moving image to be blurred, eye speed has to match object
4 types of ON OFF DSGC
lined to the cardinal directions, NSEW
fast adapting, 2 types of bipolar cells
bi-stratified dendrites
GABA antagonists
abolish DS
tells us inhibition must play a crucial role in governing direction selectivity
need to suppress null response that can be removed if GABA is blocked
starburst amacrine cells
foudn that starburst amacrine cells give GABA inhibition
have on and off starburst amacrine, bistratified direction selectivity
outputs of starburst amacrine cells
on distal dendrites, dont have any axons
distal end has swellings of varicosities that are full of vesicles that release both GABA and ACh
get bipolar cell input from proximate dendrites
what happens when SACs are ablaetd
loss of direction selectivity
- knockout SAC using molecular molecules and label with antibodies
see no labelling and dont see direction selectiviity
what is the first point where direction selectivity is observed
starburst dendrites
soma –> dendrites
3 possible mechanisms of DS in SAC
intrinsic mechanism: dendrites have properties
2. presynaptic bipolar cell input kinetics
3. SAC-SAC reciprocal 1 connections
most likely all 3
DS and dendritic filtering
dendrites delay the signal:
input far away, voltage decays with space
want slow, further away to go first to get temporal summation
blocking bipolar cells
starburst output remains DS when BPC are blocked
- inhibition in DS ganglion cell is directional so starburst connects to ganglion cell to inhibit it
large response in 1 direction and weaker in the other
SAC - SAC inhibition
starburst provide GABA (alpha 2) to eachother
excitation before inhibition gives strong depolariation
inhibition before excitation is weaker
