Electrophysiological methods were used to investigate the pretectal and telencephalic control of units within the nucleus of the basal optic root (nBOR) of the accessory optic system of pigeons. 2. Electrical stimulation of the pretectal lentiform nucleus mainly produced excitatory effects on nBOR units with temporal-to-nasal directional preference (among 109 cells, 51% were excited, 23% were inhibited and 23% were not affected) and inhibitory effects on units with nasal-to-temporal preferences (among 88 cells, 43% were inhibited, 38% were not affected, and 19% were excited). 3. Electrical stimulation of the visual Wulst (considered to be the equivalent of the visual cortex) produced mainly inhibitory effects on units with downward preferences (among 123 units, 47% were inhibited, 24% were excited and 29% were not affected), and mixed effects on units with upward preferences (among 70 cells, 30% were excited, 36% were inhibited and 34% were not affected). 4. Excitatory effects of LM stimulation had first-spike latencies ranging from 2-20 ms (mean +/- SEM, 5.5 +/- 0.7 ms), whereas latencies of W stimulation ranged from 6 to 30 ms (13.0 +/- 0.9 ms). 5. These results provide additional information about the neural substrates of the optokinetic nystagmus.
