Visual responses of morphologically identified tectal cells in the goldfish.

Intrinsic cells from the optic tectum of the goldfish were recorded intracellularly while undergoing photic stimulation, injected iontophoretically with horseradish peroxidase (HRP), and subsequently recovered in sectioned material. Unequivocal identifications were possible for 72 cells. The majority of these belonged to type I or type XIV, but types II, III, VI, IX and XIII were also observed. Type I cells exhibited a characteristic response to light flash with a strong initial hyperpolarization, and often had well defined receptive fields. Responses of type XIV vary, but often show very delayed responses, and spike potentials that do not affect the spike generating mechanism of the cell. Type XIII cells, which have bulbar axons, exhibit strong photic responses and long duration action potentials. Over 90% of cells recorded exhibited photic responses.