Multisensory cortical signal increases and decreases during vestibular galvanic stimulation (fMRI)

Functional magnetic resonance imaging blood-oxygenation-level-dependent (BO LD) signal increases (activations) and BOLD signal decreases ("deactivation s") were compared in six healthy volunteers during galvanic vestibular (mas toid) and galvanic cutaneous (neck) stimulation in order to differentiate v estibular from ocular motor and nociceptive functions. By calculating the c ontrast for vestibular activation minus cutaneous activation for the group, we found activations in the anterior parts of the insula, the paramedian a nd dorsolateral thalamus, the putamen, the inferior parietal lobule [Brodma nn area (BA) 40], the precentral gyrus (frontal eye field, BA 6), the middl e frontal gyrus (prefrontal cortex, BA 46/9), the middle temporal gyrus (BA 37), the superior temporal gyrus (BA 22), and the anterior cingulate gyrus (BA 32) as well as in both cerebellar hemispheres. These activations can b e attributed to multisensory vestibular and ocular motor functions. Single- subject analysis in addition showed distinctly nonoverlapping activations i n the posterior insula, which corresponds to the parieto-insular vestibular cortex in the monkey. During vestibular stimulation, there was also a sign ificant signal decrease in the visual cortex (BA 18, 19), which spared BA 1 7. A different "deactivation" was found during cutaneous stimulation; it in cluded upper parieto-occipital areas in the middle temporal and occipital g yri (BA 19/39/18). Under both stimulation conditions, there were signal dec reases in the somatosensory cortex (BA 2/3/4). Stimulus-dependent, inhibito ry vestibular-visual, and nociceptive-somatosensory interactions may be fun ctionally significant for processing perception and sensorimotor control.