The localization of an imaginary target under the influence of caloric vestibular stimulation in healthy adults

It is well known that fixation of an imaginary target (IT) can influence th e vestibulo-ocular reflex, but reports on the effect of peripheral vestibul ar stimulation on the localization of an IT are still lacking. In a prospec tive study, errors in pointing towards an IT without and after cold caloric vestibular stimulation (VS) were investigated in 24 right-handed volunteer s with the head tilted backwards by 60 degrees. After the stationary target had been extinguished for 120 s each subject had to point towards the targ et position as remembered in darkness. The vestibular response was recorded by electronystagmography. Without VS 73% of the volunteers showed a system atic horizontal pointing error towards the right side. VS led to an increas ed horizontal pointing error in the direction of the slow phase of the indu ced nystagmus and the degree of deviation showed a significant (P = 0.001) positive correlation (r = 0.32) with the amplitude of the calorically induc ed nystagmus. In summary, an IT is not merely a useful visual stimulus for influencing the vestibulo-ocular reflex during linear and angular accelerat ion. A peripheral vestibular stimulation is itself able to change the posit ion of an IT significantly and the extent of deviation shows a significant correlation with the amplitude of the evoked nystagmus.