Columnar organization of the optic tectum in the frog.

Cobaltous lysine complex was used to label tectal cells. Cobalt soaked into a piece of filter paper and placed onto the surface of the tectum labelled neurons in the whole thickness of the tectum below the filter paper. The labelled area was sharply demarcated from the unlabelled tectal tissue. Focal cobalt injections into different tectal layers labelled small groups of cells and the cobalt-filled structures were perpendicularly oriented to the surface of the tectum. Efferent axons could be followed into layer 7, but other lateral connections were very sparse. These results support the hypothesis that the tectum has columnar organization similar to that of the mammalian neocortex.