CVS technique
Caloric vestibular stimulation (CVS) is a routine diagnostic technique in the neurological assessment of vestibular function and brain death.
The CVS technique involves cold-water irrigation of the external ear canal (the right ear depicted above), which activates, through the semicircular canals and vestibular nuclei, brain regions in the contralateral
hemisphere. Such regions include anterior cingulate cortex (ACC) and temporoparietal areas (TPA). Contralateral activation of other areas such as the putamen (in basal ganglia) and insular cortex are not depicted.
In our use of the technique, subjects are otoscopically examined by a medical officer for any signs of ear disease or cerumen impaction prior to CVS. Participants are reminded of the CVS procedure and instructed
to report the onset of the anticipated signs of the stimulation (see below). With the subject maintaining a vertical mid-sagittal plane, head orientation is kept at 30° from the horizontal plane, thereby placing the lateral (horizontal) semicircular canal into the vertical plane for maximal stimulation. Cold (iced) water is similarly used to provide maximal stimulation and is slowly irrigated into the external auditory canal using
a 50-ml plastic syringe with a short piece of soft silastic tubing attached and positioned near the tympanum. Irrigation usually stops after 20–30 ml when the subject reports vertigo and the experimenter observes nystagmus (slow-phase direction ipsilateral to the ear stimulated). The refluent water from the external auditory canal is recovered in a plastic container rested on the subject’s shoulder underneath the irrigated ear. Any signs of ongoing nystagmus and subject’s reported vertigo usually cease 2–3 min following their onset.
For a review of the technique, its applications and a discussion of methodological issues, see Miller SM, Ngo TT (2007). Studies of caloric vestibular stimulation: Implications for the cognitive neurosciences, the clinical neurosciences and neurophilosophy. Acta Neuropsychiatrica, 19 (3): 183–203.[PDF]