A comparison of visual responses in two pretectal nuclei and in the superior colliculus of the cat.

Single unit recordings from 220 units were obtained from the nuclei praetectalis anterior (NPA) and posterior (NPP) of 30 immobilized, anesthetized cats. Quantitative analysis of pretectal (PT) visual activity was mainly based on recordings from the NPP. For comparison, 160 collicular (CS) neurons were studied. A strong sensitivity for moving objects was evident in both samples. The following main types of PT activity were categorized: (A) slow movement, direction-selective units (21%); (B) slow movement, nondirection-selective units (19%); (C) units nonselective for stimulus velocity and direction (24%); (D) jerk movement selective, nondirection-selective units (36%). Latency measurements following single shocks to optic chiasm (OX) and tract (OT) showed mainly slow conducting fiber input to the PT and CS which can be divided into two different groups by conduction properties and synaptic delay: direct W-input and delayed W-input. Fast Y-fiber input of both types, direct and indirect, was recorded at both sites, PT and CS.