The effects of state of alertness on the vestibulo-ocular reflex in normal subjects using the vestibular rotational chair.

Twenty-four subjects with normal vestibular function underwent horizontal sinusoidal harmonic acceleration (SHA) and step-velocity rotational chair assessment twice, first in a heightened state-of-alertness, and second, in a low state-of-alertness. The effects of alertness on vestibulo-ocular reflex gain and time-constant (Tc) were then examined. Although the negative effect on SHA gain had previously been widely reported, the effect on the Tc had not been studied. It was found that SHA gain and step-velocity Tc were significantly and artificially reduced with decreased alertness. On average, SHA gain was reduced by 0.1 at each test frequency and the Tc was reduced from 15.8 seconds to 10.5 seconds. Whilst on average, step-velocity initial gain was only a little affected reducing from 0.53 to 0.49. This very small difference of 0.04 was significant, however, it suggested that this measurement is less affected by patient alertness than SHA gain and Tc.