Somatotopic organization of second order neurons of the eye muscle proprioception.

Unit activity was recorded extracellularly from lamb's nucleus principalis and pars oralis of trigeminal nuclear complex following moderate manual stretching of individual extraocular muscles. The oral portion of the spinal trigeminal nucleus and the main sensory nucleus have been investigated by systematic exploration of the second-order neurons of the eye muscle proprioception. Such responses were somatotopically organized. In particular, each single extraocular muscle was represented along the main dorso-ventral axis in this manner: superior oblique and superior rectus in a dorsal layer; inferior rectus and inferior oblique in an intermediate layer, while the medial rectus and the lateral rectus were represented more ventrally. In a few experiments this representation was not observed, due to intermingling of the units. The topographic organization of eye muscle proprioception in the trigeminal nuclear complex described above closely corresponds to that reported by previous authors in the Gasser ganglion.