Elementary Cone Photoreceptor Signals In V1 Neurons

Authors

• Cyril Nyankerh, University of Alabama at Birmingham

Advisor(s)

Lawrence Sincich

Committee Member(s)

Paul Gamlin
Scott Cruikshank
Tamara Oechslin
Timothy Gawne
Timothy Kraft

School

School of Optometry

Document Type

Dissertation

Department (new version)

Vision Science

Date of Award

9-9-2024

Abstract

Daylight vision is initiated by the activation of cone photoreceptors in the retina in response to light, thereby generating spatial and temporal patterns of photoreceptor signals. Subsequent to this, the signals are combined and processed in downstream neural circuits, ultimately contributing to the formation of receptive fields of neurons in primary visual cortex (V1). Recent advances in adaptive optics (AO) have enabled imaging of the retina with near diffraction limited resolution, allowing for the probing of the visual system's processing at the resolution of individual cones. The central theme of this dissertation characterizes quantitively and qualitatively the physiological responses of macaque V1 neurons using AO microstimulation. To do this, we used an AO scanning laser ophthalmoscope with stimulation capabilities to map the receptive fields of V1 neurons at a retinal eccentricity of 2.2° using white noise and naturalistic 1/f noise movies while recording from V1 cells. Spike triggered averaging was used to map the receptive fields. The median receptive field sizes we measured for center-surround cells was 3.8 arcmin, whereas that of simple cells measured 9.84 arcmin. These field sizes were consistently smaller than those reported previously. In response to a single pixel embedded in the ongoing movies, we found substantial spike probability changes for light increments and decrements, as well as for temporal contrast conditions which lead to greater probability changes than for single pixel conditions. This pixel-targeted approach showed that cone-scale changes in stimulus conditions—representing only a small fraction of the receptive field—can be registered by V1 neurons. We also examined how signals originating from cone photoreceptors are processed in V1 by targeting cone-sized stimuli to individual cones and cone pairs, quantified with intensity response functions. We found both linear and non-linear responses to paired cone stimulation that are influenced by stimulus intensity and where the cones are located relative to the receptive field. Contrary to the idea of neurons simply weighing and summing incoming signals for spiking responses, these findings challenge the concept of a purely linear, stimulus-invariant receptive field, underscoring the need for more detailed models of V1 neurons characterized at a cone-resolved level.

ProQuest ID

https://proquest.com/docview/3101937422