Visual-vestibular interaction--an evoked potential study in normal human subjects.

Positron emission tomography (PET) was used to demonstrate temporary down-regulation of visual cortex activities associated with eye movements. The aim of the present study was to test this paradigm with visual evoked potentials (VEPs) in the visual cortex of 7 healthy human subjects during caloric nystagmus. Caloric stimulation was performed by irrigating the right or left external ear canals with 100 ml of warm water at 44 degrees C for 50 s with a head position of 60 degrees tilted backward in order to stimulate the horizontal semicircular canal. The subjects kept their eyes closed during and after caloric stimulation. For recording the VEPs, the flashlight was used for activating the visual cortex with the subject's eyes closed. In the 7 subjects, no significant difference was detected between the VEPs induced with and without caloric stimulation.