Tectopontine pathway in the cat: laminar distribution of cells of origin and visual properties of target cells in dorsolateral pontine nucleus

1. The superior colliculus projects to the dorsolateral nucleus of the pons. Retrograde transport of horseradish peroxidase (HRP) revealed that cells in the superior colliculus, which send their axons to the pons, lie in both superficial (III) and deep (IV--VII) layers. Superficial cells outnumbered deep cells. The inferior colliculus also projects heavily to the dorsolateral pontine nucleus. 2. Dorsolateral pontine visual cells were activated only by visual stimulation. Cells responsive to somatic or auditory stimulation were also found in the dorsolateral nucleus, and they too responded to only one sense modality. 3. Of the dorsolateral pontine visual cells, 69% were directionally selective. 4. Dorsolateral pontine visual cells were responsive to moving targets over a wide range of stimulus velocities. Velocities between 25 and 100 degrees/s were the most effective. No cells responded to a stationary stimulus. 5. Single-spot targets were the most effective stimuli. Stimulus size was a more important parameter than stimulus configuration. Many cells had inhibitory regions outside of their excitatory fields. 6. The excitatory receptive fields of dorsolateral pontine cells were very large (median, 1,100 deg2). 7. Nearly all receptive fields were centered in the contralateral visual hemifield, and 91% of the dorsolateral visual cells were activated from either eye. 8. We conclude that the visual cells in the dorsolateral nucleus have receptive-field properties that are similar to those of cells in the superior colliculus. The preference of dorsolateral cells for single-spot targets contrasts strongly with the multiple-spot preference of medial pontine cells, which receive their input from visual cortex.