Dogfish horizontal canal system: Responses of primary afferent, vestibular and cerebellar neurons to rotational stimulation

Abstract The activities of horizontal canal primary afferents, vestibular neurons and neurons in the auricular lobe of the cerebellum were sampled during horizontal head rotation in the dogfish Scyliorhinus canicula . Sinusoidal head rotation produces a smooth sinusoidal modulation of discharge frequency in primary vestibular afferents. The information content of this afferent signal is rather faithfully represented by the output of both the vestibular nuclei and the vestibulocerebellum. A degree of information processing does take place in that: 1. The spontaneous activity of central neurons is generally lower than that of primary afferents, with the result that many are silenced during the inhibitory portion of their response. 2. Some vestibular and cerebellar neurons responded maximally 180° out-of-phase with the ipsilateral primary afferents (type II response). 3. Information from opposite canals is integrated to produce an increased rotation sensitivity in some vestibular neurons and a bidirectional increase in firing (type III response) in other neurons. 4. At stimulus frequencies below 0.16 Hz Purkinje cells showed a steeper reduction of phase lag than granular layer units or primary afferents whereas vestibular neurons did not show a clear tendency towards reduced phase lag at lower frequencies.