Effect of transdermally administered scopolamine on vestibular function tests in humans

The effects of transdermally administered scopolamine (Scopoderm TTS) on caloric, rotatory, optokinetic and optokinetic after nystagmus were evaluated in normal subjects. Two Scopoderm TTS or two placebo were applied retro-aurally 24 hours before each test. Three parameters (maximum slow phase velocity, number of nystagmus and duration of nystagmus) of air caloric test in 9 volunteers were used. Each ear was stimulated at 20°C or 50°C air temperature for 60 sec. Gain (= peak slow phase velocity/peak head velocity) of rotatory and optokinetic nystagmus of 12 subjects was examined during the sinusoidally induced rotatory and optokinetic stimulation (amplitude 120 deg; frequency 0.1 Hz). After 60°/s optokinetic stimulation for 30 sec, optokinetic after nystagmus of 9 people was measured in the dark. Initial slow phase velocity (=average of first three slow phase velocity), number of nystagmus and duration of nystagmus were calculated. During the experiment, subjects were required to do mental arithmetic while each nystagmus was being recorded. The drug reduced the maximum slow phase velocity of caloric nystagmus, compared with the placebo. There were no significant differences between treatments in both rotatory and optokinetic tests. Scopolamine had a suppressive effect on both initial slow phase velocity and duration of nystagmus of optokinetic after nystagmus. In a accordance with to Cohen's theory, this drug acts on a velocity storage integrator of the central nervous system.