[Horizontal optokinetic nystagmus in the pigeon: role of accessory optical system]

Some characteristics of the horizontal optokinetic nystagmus (OKN) have been studied in the pigeon using monocular and binocular stimulations. The OKN is asymmetrical, temporal to nasal stimulation eliciting a larger response than a nasal to temporal one. The role of the accessory optic system (AOS) was studied by means of unilateral or bilateral lesions of the primary relays, nuclei ectomamillaris (nEM) and superficialis synencephali (nSS). Results show the existence of a synergy between nEM and nSS on the same side and between nEM and nSS on opposite sides, whereas each nucleus has an inhibitory effect upon its contralateral homologue. Some evidence was obtained which suggests the existence of an ipsilateral retinal projection to the nEM.