Visual responses of neurons in the avian nucleus isthmi

Electrophysiological responses of neurons to visual and auditory stimulation are extracellularly recorded from the pigeon isthmic area. Cobalt sulfide markings show that only visual units are localized within the nucleus isthmi pars parvocellularis (Ipc) and pars magnocellularis (Imc), while visual-auditory bimodal units are localized outside. Visual units respond to black or white targets moving through their receptive fields (RFs). The RF centers are mainly distributed in the contralaterally lower visual field. The rostral Ipc and Imc receive information from the nasal visual field, and the caudal part of the Ipc and Imc corresponds to the temporal field. Therefore, both Ipc and Imc are visual centers instead of auditory centers as described before.