The projection of the superior colliculus onto the reticular formation of the brain stem an experimental anatomical study in the cat

SummaryFollowing altogether 18 stereotactically placed lesions of different location and size in the superior colliculus the efferent fibres to the RF and their distribution were traced in silver impregnated, approximately serial sections (Nauta and Fink and Heimer methods), cut in the transverse, horizontal or sagittal plane. The projection to the mesencephalic RF was found to be almost completely ipsilateral, that to the pontomedullary RF largely contralateral. In the mesencephalic RF the fibres end in its dorsal half approximately. In the pons and medulla they supply only the medial 2/3 of the main RF, with two distinct maxima within the total field of termination. One maximum covers the rostral part of the nucleus reticularis gigantocellularis and the adjoining part of the nucleus reticularis pontis caudalis, the other occupies the rostralmost part of the latter and the caudal part of the nucleus reticularis pontis oralis. Of the precerebellar reticular nuclei the contralateral nucleus reticularis tegmenti pontis receives a distinct component of tectal fibres in a small area dorsomedially. Some fibres end in a restricted part of the nucleus reticularis lateralis and in the paramedian reticular nucleus.The tectoreticular projection appears to be organized according to the same principles as other afferents to the RF. In the main RF the areas of termination of the tectoreticular fibres coincide more or less with the areas of termination of corticoreticular, fastigioreticular and vestibuloreticular fibres. These common terminal areas are those which give off the bulk of reticulospinal fibres. Some functional implications of the pattern of organization in the tectoreticular projection are discussed.