Modulation of conscious experience by peripheral sensory stimuli.

Lack of awareness of touch associated with brain damage may transiently recover after stimulation of the vestibular system. We used positron emission tomographic regional cerebral blood flow measurements to study the neurophysiological effect of vestibular stimulation on touch imperception in a subject with a right brain lesion. We tested the hypothesis that the vestibular system aids conscious tactile perception by introducing a bias in the neural system subserving body representation. We show that in normal subjects touch and vestibular signals share projections to the putamen, insula, somatosensory area II, premotor cortex and supramarginal gyrus. In our patient a subset of these regions (right putamen and insula) was spared by the lesion and was maximally active when touch and vestibular stimulations were combined. These results support the suggestion that our phenomenological consciousness is associated with activation in circumscribed brain areas specific to the particular sensation of which we are aware.