Eye movements evoked by microstimulations in the brainstem of the alert cat.
This study maps the eye movements evoked by microstimulations in the medulla of 9 alert cats. Trains of square waves (20 microA amplitude, 0.2 msec duration, 200 Hz) were delivered through glass-covered tungsten microelectrodes (0.5-1 M omega). Movements of both eyes were recorded by the magnetic field/eye coil technique. Stimulation of the prepositus hypoglossi nucleus (PH) evoked nystagmus with ipsilaterally-directed slow phases followed by after-nystagmus with contralaterally-directed slow phases. Stimulation of the medial vestibular nucleus (MVN) induced nystagmus whose slow phases were more often ipsilaterally-directed but at time contralaterally-directed. At nearly all sites where we stimulated the reticular formation underlying prepositus and vestibular nuclei (from P4.5 to P12), we recorded versional conjugate movements. They were most often ipsilaterally-directed. Some microstimulations in the region of the medial longitudinal fasciculus evoked recentering eye movements: regardless of the initial position of the gaze (to the left as well as to the right), microstimulations given at the same place induced a movement of both eyes toward their neutral position. The amplitude of this movement was proportional to the eccentricity of the pre-stimulation position of the gaze.
Godaux
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E
Neurophysiologie, Faculté de Médecine, Université de Mons-Hainaut, Belgium.
Cheron
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G
Gravis
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F
D000818:Animals; D001933:Brain Stem / Q000502:physiology*; D002415:Cats; D004558:Electric Stimulation; D005403:Fixation, Ocular; D007002:Hypoglossal Nerve / Q000502:physiology; D009760:Nystagmus, Physiologic; D014726:Vestibular Nuclei / Q000502:physiology