Importance of the visual and vestibular cortex for self-motion perception in man (circularvection)

Circularvection (CV), the optokinetically induced perception of self-motion, is based neurophysiologically upon visual-vestibular convergence. It is yet not known which visual pathways--subcortical accessory optic tract and/or cortical striate projection--convey optokinetic information to the central vestibular system in order to make possible the convergence that has been found: the vestibular nuclei, the thalamus and the vestibular cortex. The functional significance of the visual cortex was demonstrated in 12 patients with homonymous hemianopia who neither perceived CV nor exhibited a postural destabilization when exposed to optokinetic pattern motion (yaw or roll) restricted to the scotoma. The functional significance of the vestibular cortex as well as ipsilateral visual-vestibular interaction was demonstrated in 4 (out of 20) patients with tumour lesions involving the vestibular cortex areas. They either failed to perceive CV or showed a significant increase of CV-latencies when monocular optokinetic stimulation was restricted to the ipsilateral visual cortex. Arguments for and against the following hypothesis are discussed: circularvection is induced by visual motion stimulation of the primary visual cortex which then activates vestibular nuclei neurons by descending pathways and which also informs the vestibular cortex that self-motion with a perceptual direction is involved. Determination of the velocity of CV is mediated by direct visual-vestibular cortex interaction, which most probably is also involved in the perceptual interpretation of motion perception: Self-motion versus object-motion.