CALLAWAY Ed Salk  VISION Circuits  Nov 5 2012

this lec is in Herrin 175  Monday at 4 PM...

monkey visual system.. work at Salk...

we know WHERE but want to know HOW...  neuronal microcircuits...

tells u  where things are localized but not HOW they transform info...
Area MT  receives input directly and indirec from layer 4B of primate vis cortex.

(he starts with historical review)
contribs of magno and parvocellular visual pathways from V1 to MT  1995 to 2007

****slide 1... van essen  1992:   struc and fxn of monkey visual cortex...  retinotopic areas...

  P cells = parvo  and M  cells = magno cells

pathways are segregated up to LGN and to V1

the fantasy is that they stay segregated  (to ventral and to dorsal pathways)
  but NO... there is mixing...

(fantasy is that the midget cell (which are the high res cells) feed directly into the parvo cells in LGN
and that this pathway will remain segregated in the  ventral pathway
 (and that high res spatial info will be confined only to the ventral pathway)

they are segreg to V1 but not after... we want to look at local circuits...

is there also a Parvo contrib to MT ?

retina:  midget cells:   are the parvocell input at LGN  and then go to a separate layer in V1 etc.

so, do layer 4B cells in MT have input from parvo?

pyramid neurons get mixed  parvo and magno input...  but spiny stellates only get magno input.

what is the proportion of stellate vs pyram neurons that project from layer 4B of V1 to V2 or MT?

inject rabies virus into MT to get retrograde labeling (to trace the inputs to MT)

there is a direct projection from V1 to MT...

but most projecting cells are spiny stellates  (75%)

spiny stellates only get magno input (from LGN)

do the pyramids that project to MT have parvo input?

inject CVS rabies virus...

will go retrograde and even go back another layer trans-synap so that you will see
di-synap labeled cells  (2 steps back)

so.. perhaps no parvo input to MT  (at least not direct)...

there are also layer 6 pyrams that project to MT  and they do get parvo input from LGN...

***

so, LGN  parvos go mainly to layer 4C  but also to layer 6 in V1... and those go to MT...

used photostim to check connectivity...

can predict  pyram and FS interneurons inputs by looking at  dendrites...

but not so for adapting interneurons...

so, cell type is v impt in predicting connex.

but even neighboring neurons of the same type are connected differently...

must get  level of resol of indiv neurons...

must be able to get at circuits... with molec and genet methods...

to express Cre recombinase

new rabies-based methods allow studies linking circuitry to function....

*****

Linking connex to func for cell types...

eg chandelier cells...  conserved across indivs and species...
rules of connectivity are conserved...

because each cell is connec diff.,  it's nec. to study one cell in same animal...

unique to particular cell and to partic animal...

see Wickersham in neuron 2007

see Marshel in neuron 2010

inject plasmid with 3 genes into neuron

YFP to find cell later;  TVA  ... recep for rabies virus;  
and rabies glycoprotein... so can spread to direct inputs...

see it with mcherry... spreads only to presynap cells  and goes back only one step (retrograde)

mCherry lights up  electroporated cell...

this is from Marshel et al in Neuron in 2010...

great photos...

if u see cells labeled it means they are def. connected to your cell  (but not guaranteed to see ALL inputs)

need rabies glycoprotein in order for  rabies to replicate

insertion of new genes into rabies genome...

can also insert ChR2  to check fxn...

***MICE

9 visual areas surrounding V1 in mice...  but are they retinotopic?..

wang and burkhalter 07...

jim marshel and garrett in Neuron 2011...

use calcium dye... and 2 photon imaging...

jim marshel and garrett  also looked at tuning curves for indiv neurons...

looked at 4600 cells of which perhaps 1500 were visually respons.

looked at spatial freq selectivity and to orientation selectivity and direction selectivity

looked at 9 visual areas in mouse...

dorsal parietal areas are for spatial orientaton, navigation, action

ventral/ temporal is for object and pattern recog and perception

dorsal parietal is usu more high temporal freq and low spatial freq  

but he cites Goodale..  relation of   grasping/ motor to perception...

Q1  orientation columns... 
A  wiring optimiz...  length optimiz...

mouse  tiny areas...  more effic in mouse  
squirrels do not have columns

****
mice lots of dysconjugate gaze... lots of looking up  (for predators)

Bill Newsome Q:  inputs 1000 to 5000 inputs  ... old guess...
is that right?

A  perhaps  2000 spines.....

but  one axon may connect to 4 or 5 spines  (so perhaps shud divide by 5)

Q  differ. rate of  transfection with rabies  across difft cell types?

depends on prox to cell body...

takes a while to spread to distal dendrites...

Q Tony Norcia:   how many difft inputs to MT?
A so how do u tile the space of inputs...  (eg  is there continuum of spatial freq; orientation; ocular dom;  direction tuning; stereo;

want methods   that  will actually show us... gCAMP6  get huge % of labeling...