Motion Illusion—Evidence towards Human Vestibulo-Thalamic Projections

Contemporary studies speculated that cerebellar network responsible for motion perception projects to the cerebral cortex via vestibulo-thalamus. Here, we sought for the physiological properties of vestibulo-thalamic pathway responsible for the motion perception. Healthy subjects and the patient with focal vestibulo-thalamic lacunar stroke spun a hand-held rheostat to approximate the value of perceived angular velocity during whole-body passive earth-vertical axis rotations in yaw plane. Vestibulo-ocular reflex was simultaneously measured with high-resolution search coils (paradigm 1). In primates, the vestibulo-thalamic projections remain medial and then dorsomedial to the subthalamus. Therefore, the paradigm 2 assessed the effects of high-frequency subthalamic nucleus electrical stimulation through the medial and caudal deep brain stimulation electrode in five subjects with Parkinson’s disease. Paradigm 1 discovered directional mismatch of perceived rotation in a patient with vestibulo-thalamic lacune. There was no such mismatch in vestibulo-ocular reflex. Healthy subjects did not have such directional discrepancy of perceived motion. The results confirmed that perceived angular motion is relayed through the thalamus. Stimulation through medial and caudal-most electrode of subthalamic deep brain stimulator in paradigm 2 resulted in perception of rotational motion in the horizontal semicircular canal plane. One patient perceived riding a swing, a complex motion, possibly the combination of vertical canal and otolith-derived signals representing pitch and fore-aft motion, respectively. The results examined physiological properties of the vestibulo-thalamic pathway that passes in proximity to the subthalamic nucleus conducting pure semicircular canal signals and convergent signals from the semicircular canals and the otoliths.