Cervico-ocular reflex enhancement in labyrinthine-defective and normal subjects.

The cervico-ocular reflex (COR) was elicited in 12 normal and 30 labyrinthine-defective (LD) subjects, lacking a vestibulo-ocular reflex (VOR) in the usual laboratory tests, by sinusoidal horizontal rotation of the body at 30 degrees amplitude and frequencies of 0.1, 0.2 and 0.4 Hz. The head was fixed in space and the eyes were open in total darkness. The gain of the COR was measured by relating the maximum slow phase velocity (MSPV) of the eyes to the maximum input velocity (19, 38 or 75 degrees/s) and by relating the cumulative eye displacement per hemicycle to the peak-to-peak amplitude of 60 degrees. The COR gain was below 0.25 in the normal subjects. In the LD subjects, a clear COR was observed with a gain of about 0.7 (SD 0.3) at 0.1 Hz, decreasing to about 0.4 (SD 0.2) at 0.4 Hz. There was no appreciable phase lag in 11 of the LD subjects. In 17 other LD subjects, the phase lag was close to 0 degrees at 0.1 Hz and increased to about 20-30 degrees at 0.4 Hz. Testing 4 additional normal subjects with the special instruction to attempt fixation of the knee during trunk rotation in the dark, resulted in an enhanced COR showing many "catch-up" saccades with a gain close to unity; the smooth component was also enhanced. The pattern with catch-up saccades was different from the pattern observed in most LD subjects, which closely resembled the normal VOR elicited by sinusoidal rotation. The special instruction to attempt fixation of the knee was also given to one LD subject during stimulation at 0.2 Hz.(ABSTRACT TRUNCATED AT 250 WORDS)