THE VISUAL RESPONSE PROPERTIES OF NEURONS IN THE NUCLEUS OF THE BASALOPTIC ROOT OF THE NORTHERN SAW-WHET OWL (AEGOLIUS-ACADICUS)

The nucleus of the basal optic root (nBOR) in birds is a component of the accessory optic system (AOS) which is involved in the analysis of visual flowfields normally resulting from self-motion. Using standard extracellular techniques, we recorded from 81 single-unit and multi-un it clusters in the nBOR of the northern saw-whet owl, Aegolius acadicu s, an avian species that has a visual system with frontal emphasis. Th ese cells responded best to large patterns of random dots moving eithe r upward (52%), downward (31%) or nasal to temporal (N-T; contralatera l Visual field; 15%). Only 2 units (2%) preferred temporal to nasal mo tion. 'Up' units were found in the dorsal portion of the nucleus where as 'Down' units were located more ventrally. The N-T units were found in both the lateral margin of the nucleus and ventral to the Down unit s in the lateral half of the nucleus. About half of the units tested ( 10/19) responded to stimulation of the ipsilateral as well as the cont ralateral eye. For all but one cell, the direction preference of both eyes was the same in visual space. When compared with previous studies of pigeons (Columba livia) and chickens (Gallus domesticus), these fi ndings reveal that the nBOR in ah three avian species have important s imilarities with respect to direction preference and functional compar tmentalization. Furthermore, the high proportion of binocular neurons found in the nBOR of the saw-whet owl is similar to the condition gene rally reported in frontal eyed mammals and hence may reflect adaptatio n.