Responses of single units in area 29 of cingulate cortex were examined in alert rabbits during vestibular and optokinetic nystagmus. Eye movements were measured by optically detecting the position of an infrared light-emitting diode attached to the cornea. 2. Fourteen percent of cingulate cells (68 of 477 isolated units) had responses that were correlated to the occurrence of quick phases. Latencies ranged from 60 ms before to 220 ms after the onset of the quick phase with a mean of 70 ms and standard deviation of 58 ms. Most units responded during or following quick phases, although four units had responses that preceded the quick-phase onset. 3. Unitary responses during quick phases were not due to visual field movement, since these responses occurred in the dark as well as the light. The responses were not dependent upon vestibular stimulation, since responses related to spontaneous saccadelike eye movements were observed in cingulate quick-phase neurons. 4. The majority (37 of 52) of the quick-phase neurons had a directional preference. Approximately equal numbers of directional units responded to quick phases directed ipsilaterally and contralaterally with respect to the recording site. 5. About one-fourth of the quick-phase units were bidirectional (15 of 52) with virtually equal responses to ipsilaterally and contralaterally directed quick phases. 6. Auditory and/or somatosensory responses were observed in only five of the quick-phase cells. All such multimodal units were bidirectional. 7. The quick-phase units were histologically confirmed to be primarily in area 29d of cingulate cortex. Although most cells were located in layer V, some were isolated in layer II-III. 8. Cingulate cortex has reciprocal connections with visual cortex and oculomotor-related thalamic nuclei and projects to the layers of the superior colliculus that are involved in oculomotor control. Responses to quick phases in cingulate neurons may synchronize cingulate cortex responsiveness with the arrival of new, and potentially significant, visual information.
