Adaptation of Vestibular and Somatic Autonomic Systems

Abstract

Cutaneous temperature changes and subjective sensations concomitant with repeated caloric and metopic cooling stimuli were studied quantitatively in order to observe the adaptation of the vestibular autonomic reflex system and the somatic autonomic system response.
The subjects were 17 healthy adults. Stimuli were applied three times at intervals of 6 minutes. The caloric stimulus consisted of exposing the right ear at 50°C for 60 seconds, while the metopic cooling stimulus consisted of applying an ice pack to the metopic region for 30 seconds. Subjective sensation was quantified during caloric stimulation by scoring vertigo and nausea on a six-grade scale and emesis on a two-grade scale. These scores were then totaled. During metopic cooling, stimulation by scoring cold sensations in the metopic region was on a six-grade scale.
When caloric stimulation was applied, lowered sensory scores were associated with significantly decreased cutaneous temperature variation and slow-phase velocity. Conversely, no significant changes in either cutaneous temperature variations or sensory scores were recognized when metopic cooling stimulation was applied.
These results indicate that the loci of central adaptation mechanisms, including the vomiting centers, are largely involved as sites responsible for adaptation in the vestibular autonomic reflex system.