Components of vestibular cortical function.

It is known that the functional response (e.g., nystagmus) to caloric vestibular stimulation is delayed and prolonged compared with the stimulus-response timing of other sensory systems. Imaging studies have used different models to predict cortical responses and to determine the areas of the brain that are involved. These studies have revealed a widespread network of vestibular brain regions. However, there is some disagreement regarding the brain areas involved, which may partly be caused by differences in the models used. This disagreement indicates the possible existence of multiple cortical components with different temporal characteristics that underlie cortical vestibular processing. However, data-driven methods have yet to be used to analyze the underlying hemodynamic components during and after vestibular stimulation. We performed functional magnetic resonance imaging (fMRI) on 12 healthy subjects during caloric stimulation and analyzed these data using a model-free analysis method (ICA). We found seven independent stimulus-induced components that outline a robust pattern of cortical activation and deactivation. These independent components demonstrated significant differences in their time courses. No single-modeled response function was able to cover the entire range of these independent components. The response functions determined in the present study should improve model-based studies investigating vestibular cortical processing.