Abstract
Abstract: :
Purpose: To describe the spatio–temporal organization of the retinal ganglion cell receptive field using multifocal stimulation. Methods: Responses of single ganglion cells in the isolated and perfused rabbit retina were obtained with tungsten microelectrodes. Multifocal stimulation and recording was made using VERIS proTM software combined with a custom video stimulator mounted on an Olympus microscope (Electro–Diagnostic Imaging Inc.; San Mateo, CA). The multifocal stimulus consisted of an array of hexagonal elements, each approximately 130 microns in size, which was imaged at the retinal surface. The luminance of each stimulus element was temporally modulated in a pseudo–random manner according to a binary m–sequence. Averaged responses were obtained from records of approximately seven minutes duration. These responses represent the average modulation in spike frequency (increase or decrease) during the response epoch. Ganglion cells were also characterized by their responses to diffuse stimuli delivered by an LED. Results: Analysis of the response kernels provides evidence for both excitatory (increased spike activity) and inhibitory (decreased spike activity) mechanisms which contribute to responses associated with stimulation of a single retinal location as well as modulatory effects on these responses which are associated with stimulation of neighboring regions. The temporal properties of these local and lateral interactions may also be described within limits imposed by the stimulus frame rate. Specific examples: 1. Pure ON–ganglion cell with a refractory period to full recovery of 240 ms and some degree of facilitory lateral interaction. 2. OFF–ganglion cell with a refractory period of 40 ms modulated by inhibitory lateral interactions with an approximate range of 250 microns. Conclusions: The multifocal nonlinear analysis of single unit receptive fields provides a powerful method for characterizing the temporal and spatial properties of synaptic mechanisms which shape visual signal transfer at the output of the retinal ganglion cell. The local and lateral response dynamics provide detailed tests for models of neural connectivity.
Keywords: ganglion cells • electrophysiology: non-clinical • retinal connections, networks, circuitry