Classification of turtle retinal ganglion cells

Abstract

1. Receptive fields of 78 retinal ganglion cells were analyzed for their responses to moving and stationary lights that were presented under a variety of stimulus conditions. All cells were sensitive to moving stimuli, and their receptive fields often comprised excitatory and inhibitory sub-regions. 2. Properties used in the classification included responses to stationary flashed stimuli, receptive-field organization, changes in stimulus wavelength and adaptation, movement velocity, and direction of stimulus movement. Eight functional cell classes were derived: simple, ON-sustained, annular, wavelength-sensitive, directionally selective, bar-shaped, large-field, and velocity. 3. Simple cells, representing 21% of the sample, had circular or oval receptive fields of 3-22 degrees that gave transient responses to stationary, flashed lights. Many of these cells, but not all, showed antagonistic center-surround organizations. ON-sustained cells responded for the duration of the stimulus flash or for the duration of a light flash moving through the receptive field. These units comprised 8% of the sample; they had small, circular, non-directional receptive fields and they were most sensitive to red light. Their field sizes did not vary with changes in adaptation level. 4. Annular cells (4% of the sample) gave no responses to any stimulation in the field center, but they responded strongly to stimulation in the surround area, especially to stimuli that moved very slowly through the region. Annular cells were nondirectional, with circular centers of 5-6 degrees diam and annular surround widths of 2-4 degrees. They responded best in light adaptation. 5. Wavelength-sensitive cells, similar to most of the cells sampled, were sensitive to red light when light-adapted. Some cells in addition showed input from rods under dark adaptation. Intensity-response curves for these latter cells showed clear changes from one input to the other as the cells' functional ranges were explored. Some cells responded best to short- or middle-wavelength light, but these were more rarely met. Where multiple receptor inputs could be identified, long-wavelength stimuli evoked transient responses, whereas short-wavelength stimuli favored more sustained spike trains. Wavelength-sensitive cells in this category comprised 5% of the sample.