Fig. 9.

Electrically evoked ocular countertilt using different reference electrodes. Example ocular countertilt responses during constant-rate pulse train stimulation applied to difference combinations of electrodes. A–F: 3 different types of responses seen when delivering a step change in pulse rate of 200 pps to a semicircular canal electrode with common crus reference. Although each example is recorded from a different chinchilla, all examples are representative of responses seen in each animals. The 1st example (A and B, Ch133) shows immediate onset of quick phases that begin to adapt out throughout the 40 seconds of stimulation, with an increase of frequency after stimulation stops. The 2nd example (C and D, Ch132) appears to follow the trend of an ocular countertilt, suggesting likely current spread to the otolith end organs (31/74 trials). The 3rd example (E and F, Ch128) shows a brief change in eye movement at the beginning of stimulation that quickly adapts out. The final examples compare the canal response to otolith and show representative examples of a pulse train (300 pps) delivered to the utricle and saccule stimulation with distant (G and H, Ch128), common crus (I and J, Ch128), and near bipolar (K and L, Ch128; and M and N, Ch132) references. Stimulation using distant reference elicited immediate change in angular eye position, similar to that seen during normal whole body static tilt. The saccule with common crus example follows a similar trend with immediate change in eye position but a slower incline to the final angular eye position. Using a near bipolar reference elicited 2 different types of responses: 1) a slow gradual increase in angular eye position, following the low-pass filter behavior of the otolith end organs, and 2) a delayed sudden change in angular eye position after stimulation onset.