Static tilt may modify the value of nystagmus asymmetry

In awake pigeons (Columba livia) we investigated the horizontal cervical and ocular nystagmuses which were induced by monaural stimulation of the lateral semicircular canals by the parathreshold sinusoidal currents. The value of nystagmus asymmetry (by the average velocities of slow components) with a normal orientation of the bird's head was compared with that in static head tilts in the sagittal and frontal planes. In the normal head position depolarization of the lateral canals evoked a stronger response than hyperpolarization of an equal value indicating that Ewald's second law is justified for the weak suprathreshold stimuli. It was found that the static tilts modify the value of nystagmus asymmetry. These changes are connected with the asymmetric modifications of the otolithic activities in tilts. This feature of the canal-olithic interaction should be taken into consideration in estimation of the results of the caloric test one of the obligatory conditions of which is static tilt.