Lay summary
Patients with vestibular disorders frequently have disabling disturbances of perception. Large areas of the cerebral hemispheres and the cerebellum receive information from the vestibular, visual and somatosensory systems which is integrated within a vestibular cortical network into an accurate perception of spatial orientation. Interrupting the pathways that process information about the direction of gravity and angular velocity leads to impairment of the internal estimate of gravity and the perception of body motion. The strategy of this research is to use repetitive transcranial magnetic stimulation (rTMS) to produce transient focal lesions that allow study of acute loss of function within the central vestibular pathways at the very beginning of adaptation. Our underlying hypothesis was that the immediate effects of a lesion in the cerebellum will be to affect ocular motor control of vestibular reflexes and perception alike, but with a cortical lesion there will be dissociation between ocular motor control and perception. We combined vestibular stimulation (rotating turntable) and eye movement recordings (scleral search coils) with rTMS and psychophysical instruments assessing self-orientation in space. (1) We analyzed the internal estimate of gravity after applying rTMS to vestibular cortical structures and observed significant changes in the estimated direction of gravity depending on the site of rTMS in a majority of subjects. These deviations showed a delayed (up to 60min) peak before decaying again. (2) We explored rotatory perception and eye movements after applying rTMS to vestibular cortical structures. Inducing lesions within cortical areas resulted in significantly shortened perception of angular velocity and unchanged vestibulo-ocular responses. - This research underlines the key role of the temporo-peri-Sylvian vestibular cortex in the perception of vestibular information and offers a starting point for further exploration of how vestibular information is centrally processed and how adaptation to acute lesions within central vestibular pathways evolves. Eventually these results may provide helpful in making major inroads into the understanding and eventually treatment of the often incapacitating symptoms of patients with vestibular disease.