Neurophysiological Organization of the Superior Colliculus Pathways Related to Gaze Control

Abstract

To elucidate the role of the superior colliculus in gaze control, intracellular responses in superior colliculus neurons (tectospinal, TS and tectoreticular, TR) to electrical stimulation of the vestibular nerve, the optic disk and contralateral superior colliculus were studied in chloralose-anesthetized cats.
1) Stimulation of the contralateral optic disk typically produced EPSPs in TS and TR neurons with disynaptic and polysynaptic latencies. Ipsilateral optic disk stimulation induced only polysynaptic EPSPs. Trisynaptic EPSPs were recorded following stimulation of the contralateral vestibular nerve. Polysynaptic EPSPs and EPSPIPSP sequences were evoked from the ipsilateral vestibular nerve. TS and TR neurons received excitatory inputs more consistently and strongly from the contralateral optic disk and vestibular nerve than from the ipsilateral ones.
2) Responses to sinusoidal oscillation indicate the presence of at least semicircular canal inputs to tectal neurons.
3) Vestibular afferent volleys converge on and facilitate interneurons which mediate trisynaptic retinotectal transmission. Visuovestibular interaction at the level of the interneurons may play an important role in visually triggered movement (gaze) accompanied by head movement.
4) Stimulation of the contralateral superior colliculus evoked monosynaptic IPSPs in both TS and TR neurons. It is very likely that these monosynaptic IPSPs partly participate in the production of tectotectal inhibition as was suggested from lesion experiments. Tectotectal projections which may mediate such inhibition were revealed by retrograde transport of HRP.