Interhemispheric projections of the optic tectum in pigeon.

The anatomical patterns of intertectal pathways in pigeon (Columba livia) were studied with modifications of the Nauta-Gygax silver technique following discrete unilateral tectal lesions. No homotopic connections between the two optic tecta were found. The data do not support an anatomical basis for the behavioral observation of interhemispheric reversal of left-right mirror-image patterns in monocularly trained pigeons. Degenerated fibers of passage were identified in the tectal commissure, the posterior commissure, the ventral tegmental decussation and the supraoptic decussations. Preterminal fields were identified in the contralateral substantia grisea perinventricularis of the tectum, lateral mesencephalic reticularnuclei, area pretectalis, nucleus linearis caudalis, nuclues posteroventrialis, and lateral geniculate nucleus, pars ventralis. The possible significance of these findings is discussed with reference to behavioral, electrophysiologic and neuroanatomic studies.