Somatotopic representation of eye muscle proprioception within the superior colliculus of the lamb

Abstract

A somatotopic organization of the extraocular muscle proprioceptive afferent projection was observed in the superior colliculus of the lamb. Units responding to the stretching of each extraocular muscle were recorded along the dorsoventral axis in the superficial layers of the superior colliculus as follows: the inferior rectus and the inferior oblique were represented in the most dorsal layer of the superior colliculus, the superior rectus, and the superior oblique muscles in the intermediate layers, and the lateral and the medial recti in the deepest layers. The superior collicular sites influenced by stretching the extrinsic eye muscles could be activated by single-shock electrical stimulation of the cellular pool of the dorsal part of the semilunar ganglion and by stimulation of both the nucleus principalis and the pars oralis of the trigeminal nuclear complex ipsilaterally, where the eye muscle proprioception is represented. Our findings indicate for the first time that in the superior colliculus a somatotopic map of extraocular afferent input is present; the significance of this projection is discussed in relation to the control of head movements and extraocular proprioception.