Temporal tuning and nonlinearity of intraretinal pathways in turtle: effects of temperature, stimulus intensity, and size.

Abstract

Flash responses, amplitude and phase transfer functions, and nonlinearities were measured in turtle retina for pathways with photoreceptor inputs and outputs from horizontal (HC), hyperpolarizing bipolar (HBC), sustained amacrine (AC), and on-off ganglion (GC) cells. Flash responses slowed and attenuated in all cells as temperature decreased. White-noise transfer properties of sustained-type cells (HC, HBC, AC) were of low- or bandpass type; high-frequency cut-off (fc) and phase crossover frequency decreased with temperature. fc increased as spot diameter was increased. Nonlinearity of these sustained-response pathways (distortion product frequencies in response to a sum-of-sinusoids input probe) increases with intensity and may depend on amplitude saturation limiting. On/off GC synaptic and spike activity increased as spot diameter decreased and intensity increased. Amplitude transfer functions had a low-frequency peak (PSP activity) and monotonically decreasing amplitude vs. frequency shape (spikes and transient PSP activity). Nonlinearity increased with stimulus intensity; it was maximal with 1 mm spot size, less with smaller (500 micron) and larger (5 mm) spots. It may depend on the functional equivalent of full-wave rectification (on-off response).