Polarization sensitivity in the crayfish optic lobe: peripheral contributions to opponency and directionally...

1. Polarization sensitivity (PS) was examined in nonspiking interneurons, tangential cells, of the crayfish optic lobe. Stationary PS profiles were measured with pulses of illumination at fixed intensity and varied evector orientation (theta). Dynamic polarization responsiveness was examined with a rotating polarizer. The dynamic response was assessed with variations in rotation velocity and direction and for variations in intensity. 2. Eighty percent of the cells tested were polarization sensitive. These were divided into two types. Type I cells exhibited PS magnitudes comparable with those of photoreceptors and lamina monopolar cells in the same species. Most type I cells exhibited a directionally selective response to a rotating polarizer. 3. Type II cells exhibited PS magnitudes substantially higher than those observed in lamina neurons. These cells also revealed evidence for a polarization opponency mechanism. 4. The results are interpreted in terms of a general hypothesis for polarization feature detection, on the basis of four principles. 1) Most or all tangential cells are subject to inhibition. 2) The inhibitory pathway is polarization sensitive. 3) If the theta producing the maximum response at fixed stimulus intensity (theta max) of the inhibitory input is similar to theta max - 90 degrees of the excitatory input, then the inhibition forms the basis of a polarization opponency mechanism. 4) If theta max of the inhibitory input is similar but not identical to theta max of the excitatory input, then the inhibitory input provides a basis for directionally selective polarization vision.