title: Illusory self-motion perception evoked by caloric vestibular stimulation in sitting versus supine body positions.
abstract: The purpose of this study was to determine (i) if a change in the body position that alters the somatosensory afferentation and thus the signal integrated by sensory interaction influences the illusory self-motion perception evoked by cold calorics. If yes, (ii) is the direction of the provoked nystagmus also changed? The vestibular system in 47 healthy subjects was stimulated calorically with 20°C water while in supine and sitting positions but with the head fixed. After each procedure the subjects were asked to describe their self-motion experience, and the provoked nystagmus was analyzed. In 45.7% of these subjects a sensation of yaw rotation was reported while in the sitting position, whereas only 9.6% had this sensation while in the supine position. However, when in the supine position the experience of roll rotation dominated, i.e., 52.1% compared to 5.3% while in the sitting position. Pitch rotation was felt only in the sitting position by 4.3%. There was no such sensation in the supine position. The perception of a full-cycle rotation dominates in the sitting position. In the sitting position 20% of the subjects reported eccentrical head rotation along the circumference of a cone-the top of the cone was located in the neck region. Linear self-motion sensations did not differ in the two positions. The evoked nystagmus in both positions was only horizontal. In conclusion, a change in body position with respect to the gravity vector, while head position is fixed, causes a change in the somatosensory afferentation and modifies the integrated sensory signal by sensory interaction. In turn it influences the self-motion perception evoked by calorics. A change in body position does not affect the direction of nystagmus.
authors.affiliation: University Hospital of Neurology and Psychiatry, 4-th km, Tzarigradsko Shosse Boulevard, 1113 Sofia, Bulgaria. Electronic address: kolev_ogi@yahoo.com.
authors.forename: Ognyan I
authors.initials: OI
authors.lastname: Kolev
authors.affiliation: University Hospital of Neurology and Psychiatry, 4-th km, Tzarigradsko Shosse Boulevard, 1113 Sofia, Bulgaria. Electronic address: spacegeorgieva@abv.bg.
authors.forename: Spaska
authors.initials: S
authors.lastname: Georgieva-Zhostova
mesh_terms: D000328:Adult; D005260:Female; D006801:Humans; D007088:Illusions / Q000502:physiology*; D008297:Male; D008875:Middle Aged; D009039:Motion Perception / Q000502:physiology*; D009760:Nystagmus, Physiologic / Q000502:physiology*; D010812:Physical Stimulation / Q000379:methods; D011187:Posture / Q000502:physiology*; D011601:Psychophysics; D012399:Rotation; D012649:Self Concept
keywords: Caloric; Illusion; Perception; Self-motion; Somatosensory; Vestibular