[Single unit activity in the nucleus ectomamillaris (nem) during optokinetic nystagmus, in the pigeon]

Extra-cellular recordings of single units were obtained in the nucleus ectomamillaris (nEM) in waking Pigeons, during optokinetic nystagmus (OKN). OKN was obtained for 8 directions of stimulation (horizontal, vertical and oblique) in monocular and binocular vision. For half of the units the responses were synchronized, showing activation during the slow-phase and inhibition during the fast phase of the OKN. This response pattern was more common for the horizontal OKN, both in the Nasal to Temporal (N-T) and in the Temporal-to-Nasal (T-N) directions. With contralateral stimulations, most cells showed directional selective responses for upwards and backwards directions, the activity being inhibited for the other directions. Some units showed a less marked directional selectivity or were unaffected by the stimulations. Ipsilateral stimulations provoked no directional selectivity, but rather a reduction of the firing level. With binocular stimulation, responses were very close to those obtained with contralateral stimulation, with an increase of the directional selectivity. The nEM seems to be involved in the control of OKN, specially for the N-T and upwards directions, and less significantly for the T-N direction.