Tactile neurons of the superior colliculus of the cat: input and physiological properties

Neurons in the strata intermediale and profundum of the cat superior colliculus (SC) previously have been shown to be organized somatotopically and to respond to tactile stimuli. The stimulus properties required for neuronal activation suggest that these neurons are excited by inputs from selected classes of high-velocity, sensitive cutaneous mechanoreceptors, and that stimulus-response relationships indicate only a narrow range of information concerning stimulus magnitude. The properties of these neurons have been interpreted as serving a role in stimulus detection that recovers slowly and may be best suited for directed attention and orientation behavior. The input to the SC was studied by injection of horseradish peroxidase (HRP) for retrograde labeling of neurons projecting to this region. The main inputs subserving the tactile pathway are the principal trigeminal nucleus and the rostral portion of the spinal V subnucleus oralis and the main cuneate nucleus. Sparser labeling was found in other somatic relays, including the gracile and lateral cervical nuclei and posterior portion of the spinal trigeminal complex. Several other projections relating to visual mechanisms are also described.