Lecture 4 – Vision 3 – The

All lecture material from the following two links: 1) http://hubel.med.harvard.edu/book/bcontex.htm 2) http://www.ib.cnea.gov.ar/~redneu/2013/BOOKS/Principles%20of%20Neural%20Science%20- %20Kandel/gateway.ut.ovid.com/gw2/ovidweb.cgisidnjhkoalgmeho00dbookimagebookdb_7c_2fc~32.htm

Raghav Rajan Bio 354 – Neurobiology 2 January 21st 2015

1 From the last two classes ...!!

● Is there a difference in which percept is predominant? (Harini)

● What happens to percepts in split-brain patients? (Sahana)

● What happens in induced synesthesia?

● Why do you see an after-image with opposite colours much like a photo negative? (Gaurav)

● Cone opsins – how do they work?

● Why 3 pairs of extra-ocular muscles?

●

2 Retinal processing

● Photoreceptors – graded potentials (no spikes)

● Photoreceptors are depolarised at rest – dark current

● hyperpolarizes the photoreceptors – cGMP dependent mechanism ● Output of the retina consists of ON-center, OFF-surround RGCs and OFF-center, ON-surround RGCs

● How does this arise?

● What are the responses of other cells?

● What processing goes on in the retina?

3 Receptive fields of RGCs – output of retina

● Stephen Kuffler was the first to find these responses in the cat

● Diffuse light throughout the field did not evoke any responses! (earlier research)

● Cat was a good choice because of no motion- selective cells, no color complications

4 Receptive fields

● Useful for predicting responses of neurons to

● Not obvious from the wiring diagram

5 Wiring diagram of retina

6 Receptive fields of neighbouring RGCs

● Neighbouring RGCs have considerable overlap in their receptive fields

7 Size of receptive fields

● Size measured by either size on retina or angle

● Primate retina, near fovea – ~10um or ~0.017degrees

● Further out, size of receptive field centers increase, size of receptor population connecting to RGCs (direct pathway)

increases and falls 8 Receptive fields of RGCs – output of retina

● Stephen Kuffler was the first to find these responses in the cat

● Diffuse light throughout the field did not evoke any responses! (earlier research)

● Cat was a good choice because of no motion- selective cells, no color complications

9 How do bipolar cells respond?

10 Bipolar cells also have center-surround receptive fields

● Two types – ON-center and OFF-center

http://webvision.med.utah.edu/book/part-v-phototransduction-in-rods-and-cones/bipolar--pathways-in-the-vertebrate-retina/ 11 Direct pathway to ON and OFF center bipolar cells

● Cones/rods – hyperpolarized by light ● ON center bipolar cell – depolarized by light in center – Inhibitory connection from cones/rods ● OFF center bipolar cell – hyperpolarized by light in center – Excitatory connection from cones/rods

12 ON and OFF bipolar cells - mechanism

● Photoreceptors release only 1 – glutamate

● OFF bipolars express ionotropic receptors

● ON bipolars express mGluR6, which links to TRPM1-L channels, non- selective cation channel 13 http://retina.anatomy.upenn.edu/~noga/noga.html Indirect pathway for SURROUND

● through horizontal cells

● GABA used as neurotransmitter

● Horizontal cells are thought to contribute to most of SURROUND responses 14 CENTER-SURROUND interactions

● Horizontal cells mediate surround interactions

http://thebrain.mcgill.ca/flash/a/a_02/a_02_cl/a_02_cl_vis/a_02_cl_vis.html 15 Human retina has 4 major types of RGCs

● Midget (M) cells – 80% - project to parvocellular pathways – small cells – slow responses – colour, details ● Parasol (P) cells – 10% - project to magnocellular pathways – big cells – fast responses – movement ● Bistratified cells

● Light sensitive RGCs 16 http://webvision.med.utah.edu/book/part-ii-anatomy-and-physiology-of-the-retina/morphology-and-circuitry-of-ganglion-cells/ Dorsal and ventral streams – M cell and P cell pathways

BIO 354 - Neurobiology 2 17 http://www.ib.cnea.gov.ar/~redneu/2013/BOOKS/Principles%20of%20Neural%20Science%20- %20Kandel/gateway.ut.ovid.com/gw2/ovidweb.cgisidnjhkoalgmeho00dbookimagebookdb_7c_2fc~31.htm Actually lots more cell types in retina

● Don't know what most of these cells are doing

18 http://wws.weizmann.ac.il/neurobiology/labs/ulanovsky/sites/neurobiology.labs.ulanovsky/files/uploads/schneidman_compulsory_reading_mastland_2001_gollisch _meister_2010.pdf More complicated processing too

● Retina has direction selective ganglion cells (rabbit, frogs)

● Color comparisons are done by RGCs

19 Starburst amacrine cells are direction selective – input to direction selective RGCs

● Selective for outward motion

● Timing of excitation and inhibition determines motion selectivity 20 http://www.sciencedirect.com/science/article/pii/S096098220602611X Distribution of S, M and L cones in the human retina

● Diagram of distribution based on data

http://www.cis.rit.edu/people/faculty/montag/vandplite/pages/chap_9/ch9p1.html

21 Colour comparison computations start in the retina

● a – Foveal that does M–L

● b – Foveal Midget cell that only connects to L cones

● c – Peripheral midget cell Some bias in the connections of this cell

● d – Small bistratified ganglion cell does S – (M+L)

http://neurosurgery.stanford.edu/research/chichilnisky/PDFs/Field2010-NV.pdf

22 Retinal processing and output

● Center-surround organisation of receptive fields – Basically codes for – compares illumination of center with surround ● Two different pathways for responding to light increases and light decreases – ON-center and OFF-center RGCs ● M and P cell pathways

● Lateral inhibition, convergence, etc.

● Direct pathway – photoreceptor --> Bipolar cell --> RGC

● Indirect pathway – through horizontal and amacrine cells – SURROUND

● More complex responses – motion sensitivity, colour comparisons, etc. in retina itself 23