Two pathways from the facial skin to the superior colliculus in the rat.

In response to single shock stimulation of the facial skin, the field potential of two negative waves (N1 and N2) appear in the intermediate layers of the rat superior colliculus (SC). From the experiments of functional ablations of the cortical facial area, the N1 wave was ascribed to the post-synaptic activity mediated by the direct trigemino-tectal pathway whereas the N2 wave to that mediated by the trigemino-cortico-tectal pathway. Single unit recordings also confirmed the existence of two pathways from the facial skin to the intermediate layers of SC.