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SIGNAL PROCESSING BY THE MAMMALIAN RETINA
NEAR ABSOLUTE VISUAL THRESHOLD
by
Haruhisa Okawa
A Dissertation Presented to the
FACULTY OF THE GRADUATE SCHOOL
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillment of the
Requirements for the Degree
DOCTOR OF PHILOSOPHY
(NEUROSCIENCE)
August 2009
Copyright 2009 Haruhisa Okawa
Object Description
| Title | Signal processing by the mammalian retina near absolute visual threshold |
| Author | Okawa, Haruhisa |
| Author email | hokawa@usc.edu; harusam@hotmail.com |
| Degree | Doctor of Philosophy |
| Document type | Dissertation |
| Degree program | Neuroscience |
| School | College of Letters, Arts and Sciences |
| Date defended/completed | 2009-05-22 |
| Date submitted | 2009 |
| Restricted until | Restricted until 08 Jul. 2010. |
| Date published | 2010-07-08 |
| Advisor (committee chair) | Sampath, Alapakkam |
| Advisor (committee member) |
Hirsch, Judith Chen, Jeannie Zhang, Li Hinton, David |
| Abstract | When few photons are available, such as on a moonless night, our vision is limited by the probability of photon absorption in rod photoreceptors, and the reliable transmission of light-evoked signals through the retina. Dark-adapted rod photoreceptors are capable of reliably signaling single photon absorptions. However, these single photon responses are challenged by neural noise arising from rod photoreceptors themselves, and the subsequent retinal circuitry. Rod bipolar cells, the second-order neurons specialized for low light level vision, pool 20 - 100 rod inputs. This convergence imposes on rod bipolar cells the difficult task of identifying sparse single photon responses among the majority that generate noise. It has been shown that saturation within the postsynaptic signaling cascade in the rod bipolar cells can effectively eliminate signals from rods whose amplitudes are statistically dominated by noise near absolute visual threshold. My first study emphasizes the delicate match between the signal-to-noise ratio of the rod photoresponse and the properties of the signaling cascade in the postsynaptic rod bipolar cells. In particular, I provide evidence that the improved signal-to-noise ratio in rod photoreceptors does not guarantee improved behavioral performance if the rod bipolar signaling cascade is not well-tuned to the rod signal-to-noise ratio. In my second study, I show that two splice variants of the heterotrimeric G-protein alpha subunit, Goα, are involved in the signaling cascade of On-bipolar cells. In rod (On) bipolar cells these subunits may together subserve the fine-tuning of the stoichiometry in the signaling cascade to improve the detection of light near absolute threshold. Collectively, my work demonstrates how the signaling cascade in the rod bipolar cells can be fine-tuned to the rod inputs to improve vision near absolute threshold, and how such adjustments are limited by biological constraints. |
| Keyword | reitna; physiology; absolute visual threshold |
| Language | English |
| Part of collection | University of Southern California dissertations and theses |
| Publisher (of the original version) | University of Southern California |
| Place of publication (of the original version) | Los Angeles, California |
| Publisher (of the digital version) | University of Southern California. Libraries |
| Provenance | Electronically uploaded by the author |
| Type | texts |
| Legacy record ID | usctheses-m2334 |
| Rights | Okawa, Haruhisa |
| Repository name | Libraries, University of Southern California |
| Repository address | Los Angeles, California |
| Repository email | http://www.usc.edu/isd/libraries/services/ask_a_librarian/email/ |
| Filename | etd-Okawa-2989 |
| Archival file | uscthesesreloadpub_Volume14/etd-Okawa-2989.pdf |
Description
| Title | Page 1 |
| Full text | SIGNAL PROCESSING BY THE MAMMALIAN RETINA NEAR ABSOLUTE VISUAL THRESHOLD by Haruhisa Okawa A Dissertation Presented to the FACULTY OF THE GRADUATE SCHOOL UNIVERSITY OF SOUTHERN CALIFORNIA In Partial Fulfillment of the Requirements for the Degree DOCTOR OF PHILOSOPHY (NEUROSCIENCE) August 2009 Copyright 2009 Haruhisa Okawa |
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