Vestibular reflexes in neck and forelimb muscles evoked by roll tilt.

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Abstract
Vestibular reflexes evoked in neck and forelimb extensors by roll tilt were studied in 2 populations of decerebrate cats: 1 with intact labyrinths and 1 with plugged semicircular canals but functioning otolith organs. In animals with intact labyrinths, the electromyogram (EMG) response in both neck and forelimb is compensatory, the side-down limb and side-up neck are activated, which would serve to right the body and to right the head on the neck. When tested with sinusoidal roll tilt of 0.01-2 Hz, the maximum response occurs at the extremes of tilt, with a slight phase lead (reposition) and gain increase developing at the higher frequencies. In canal-plugged cats, the pattern of the reflex at low frequencies is the same as in normal cats, but the dynamics differ at frequencies above 0.1 Hz. The reflex gain is lower across the frequency bandwidth and the phase of the response shows a progressive lag approaching 180.degree. as the frequency increases. The otolith organs are reponsible for the low-frequency response seen in neck and forelimbs. At higher frequencies, when this response develops a large phase lag, additional input from the semicircular canals serves to maintain a compensatory reflex.