Depth-marking the proximal negative response in the pigeon retina.

The depth distribution of proximal negativity in the pigeon retina was investigated with a dye-marking technique. Proximal negativity is recorded in three stages as the retina is penetrated. At and near the surface (level 1) the response is small and phasic: next, during "level 2" the one response exceeds the off response in amplitude: then, at "level 3" the off response exceeds the on response in amplitude. The dye marks were located in thin light microscope sections; they were about 20 micrometer in diameter, and were associated with larger areas of tissue damage. Level 3 dye marks were centred at the middle of the inner plexiform layer, and level 2 dye-marks were distributed more proximally. The amplitude maxima of the PNR are close to the middle of the inner plexiform layer, and are separated by approximately 15 micrometer.