Cerebral activation was investigated with functional magnetic resonance imaging (fMRI) during galvanic stimulation of the mastoid in 6 normal volunteers. Cutaneous stimulation at the neck C4-5 level served as a control. During mastoid stimulation, bilateral vestibular activation occurred in the posterior insula (parietoinsular vestibular cortex, PIVC), the transverse temporal (Heschl's) gyrus, and thalamic pulvinar. The cutaneous pain elicited by galvanic stimulation caused bilateral activity of the medial part of the insula and the anterior median thalamus. Thus, galvanic stimulation at the mastoid level activates cortical areas of three different sensory systems in the insulathalamic region, the vestibular, the auditory, and the nociceptive systems.
