EXPERIhIENTAL R’EUROLOGY 60, 337-346 (1978) Optic Nystagmus and Vestibular Nuclei: Unitary Activity of Vestibular Neurons during Nystagmus LAURA PETROSIKI -END DIAKA TROIANI l Imtitutc of H~rrtrrr Physiology, UgtiTlcrsit& Cattolica drl S. Cllovc, Rorrkc 00168, Italy Rcccivcd Ocfobrv 23, 19iT; rcvisioll rcc&rd Fchtary 2, 1978 The behavior of 102 vestibular neurons during optic nystagmus was investigated in 25 guinea pigs with extracellular microelectrodes. The recorded vestibular neurons were electrophysiologically identified by their orthodromic response to ipsilateral labyrinthine stimulation and by anti- dromic activation from the medial longitudinal fascicle. Of the 102 recorded units, 92 were modulated by the electrical stimulation of at least one optic nerve. The presence of vestibular neurons sensitive to the direction of nystagmus induced by labyrinthine or optic stimulation was also analyzed. INTROI>UCTIOi% In the preceding paper (18) we demonstrated that acute total destruc- tion of the vestibular nuclei abolishes optic nystagmus elicited by electrical stimulation of the optic nerves. Analyzing the interactions between labyrin- thine and optic nystagrnus, an enhancement of nystagmus frequency for ipsiversive nystagmi and a mutual extinction for contraversive nystagmi were observed. In addition, ocular movements of visual origin have been widely reported to be related to vestibular neuronal activity (1, 2, 4-7, 9, 11, 19). On this basis, the aims of the present research were (i) to examine the responses of electropl~ysiologically identified vestibular neurons to stimulation of single optic nerves, and (ii) to compare vestibular neuronal behavior during optic and labyrinthine eye nystagmus. 1 This research was supported by a grant from the CNR. We gratefully acknowl- edge the histological and technical assistance of Miss B. Zannoni. We are also indebted to Dr. V. E. Pettorossi for his helpful criticism and to Mr. R. Mancinelli for technical aid. 337 0014-4886/78/0602-0337$02.00/O Copyright 0 1978 by Academic Press, Inc. All rights of reproduction in any farm reserved.