Vestibulo-ocular reflexes in the adult sea lamprey

Vestibulo-ocular reflexes were elicited in isolated preparations of small adult sea lampreys (Petromyzon marinus). Mechanical stimulation of the labyrinths or electrical stimulation of the vestibular nerves produced stereotyped, conjugated eye movements (Table 1) and appropriate electrical activities in individual extraocular muscles (Fig. 1). No inhibition of discharges in motor nerves was observed during stimulation of opposing reflexes. Likewise, nystagmus was never seen during continued stimulation. The primitive eye reflexes of the lamprey probably correspond to the simple excitatory pathways from single ampullae to individual eye muscles of higher vertebrates.