טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentTwig Gilad
SubjectColor Information Processing in the Distal Turtle Retina
under Bright Light Illumination
DepartmentDepartment of Medicine
Supervisor Professor Emeritus Ido Perlman


Abstract

Chromaticity horizontal cells (CHCs) are 2nd order neurons that are the first to exhibit color opponent behavior in the turtle retina. They are also characterized by large receptive fields, and thus, play a role in spatial and color information processing. The major goals of this work were to reveal the contribution of CHCs to (i) background adaptation, (ii) spatial coding and (iii) wavelength discrimination. These goals were achieved by recordings the photoresponses of cone photoreceptors and horizontal cells in the everted eyecup preparation of the turtle Mauremys caspica.

Background adaptation: Comparing the effects of cone iso-luminant backgrounds in Red/Green horizontal cells indicated that contrast detection and sensitivity were improved when "opponent wavelengths" were used for background and light stimulation. Changes in the voltage range of operation (response compression or augmentation) and synaptic mechanisms are suggested to contribute to these phenomena.

Spatial-chromatic interaction: The receptive field size was found to be intensity- and wavelength-dependent. These differences arise from the intrinsic properties of the horizontal cells' syncytia and indicate that color information processing depends upon wavelength, intensity and spatial pattern.

Wavelength discrimination: The spectral properties of Red/Green and Yellow/Blue C-type horizontal cells were studied using action spectra and large amplitude photoresponses. Variability was found between retinas but not within a retina. The line element analysis was used to compare electrophysiological prediction of wavelength discrimination to behavioral measurements. My analysis supports the notion that these two opponent channels, Red/Green and Yellow/Blue may account for the results obtained by behavioral tests.