Distribution of synaptic terminals from prepositus neurones on the collicular maps

The distribution of synaptic terminals was quantified in the superior colliculus (SC) following injections of Phaseolus vulgaris-Leucoagglutinin in the ventral prepositus hypoglossi nucleus (PH) and adjacent reticular formation. Labelled axons distribute terminals within the intermediate and the deep layers on both sides. Within the former, their distribution reproduces the representation of the visual hemifield on the same side as the injected PH. Additionally the density of boutons gradually increases in the contralateral SC, from the projection of the area centralis towards the periphery, i.e. towards regions coding for larger saccades. Such a differential synaptic input may provide the neuronal basis for a temporal to spatial transformation of the feedback signal controlling gaze shifts. A theoretical model is proposed.