Role of somatosensory and/or vestibular sensory information in subjective postural vertical in healthy adults

Abstract

The body's subjective postural vertical (SPV) has been thought to be affected by somatosensory information. How the SPV is perceived based on what types of somatosensory information has not been determined experimentally by manipulating somatosensory conditions. We investigated the effects of disturbing the somatosensory information from a seat pad and/or vestibular sensory information on the SPV in 15 healthy adults. Their SPV values were measured under four conditions (control, somatosensory, vestibular, and somatosensory + vestibular) in random order. The average and absolute SPV values were measured. In the somatosensory condition, a foam rubber pad was placed on the seating surface and the subject's SPV was measured. In the vestibular condition, the SPV was measured during galvanic vestibular stimulation (GVS). The somatosensory + vestibular condition was used to measure the SPV during combined somatosensory and vestibular stimulation. The mean SPV value was significantly increased in the somatosensory + vestibular condition compared to the other three conditions. The absolute value of SPV was significantly increased in the somatosensory and somatosensory + vestibular conditions compared to the control and vestibular conditions. There was no significant difference in the average or absolute SPV values in the vestibular condition compared to the other conditions. There was no significant difference between SPV errors when somatosensory information was disturbed or when somatosensory + vestibular information was disturbed. When the somatosensory information from the seat was disturbed, the SPV error increased, and it also shifted under the influence of the vestibular sensory information modulation. These results indicate that somatosensory information from the seat plays an important role in SPV in healthy adults.