Velocity storage in the human vertical rotational vestibulo-ocular reflex

• Published in: Experimental brain research Vol. 209; no. 1; pp. 51 - 63
• Main Authors: Bertolini, G., Ramat, S.
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer-Verlag 01.03.2011; Springer; Springer Nature B.V
• Subjects: Adult; Asymmetry; Biological and medical sciences; Biomedical and Life Sciences; Biomedicine; Brain - physiology; Ear and associated structures. Auditory pathways and centers. Hearing. Vocal organ. Phonation. Sound production. Echolocation; Female; Fixation, Ocular - physiology; Fundamental and applied biological sciences. Psychology; Gravity Sensing - physiology; Head Movements - physiology; Human subjects; Humans; Male; Middle Aged; Motion Perception - physiology; Motor control and motor pathways. Reflexes. Control centers of vegetative functions. Vestibular system and equilibration; Neurology; Neurosciences; Nystagmus, Optokinetic - physiology; Otolithic Membrane - physiology; Physiological aspects; Postural Balance - physiology; Psychological aspects; Reaction Time - physiology; Reflex, Vestibulo-Ocular - physiology; Research Article; Rheology - methods; Rotation - adverse effects; Saccule and Utricle - physiology; Semicircular Canals - physiology; Velocity; Vertebrates: nervous system and sense organs; Vestibulo-ocular reflex; Italy; Directional asymmetry; VSM; Pitch VOR; Vertical rVOR; Gravity; Human; Monkey; Rotation axis; Rotation; Inner ear; Organ of hearing; Vertebrata; Mammalia; Asymmetry; Semicircular canal; Otolith; Vestibuloocular reflex; Primates; Vestibular system; Time constant
• ISSN: 0014-4819; 1432-1106
• DOI: 10.1007/s00221-010-2518-6

Human horizontal rotational vestibulo-ocular reflex (rVOR) has been extensively investigated: the horizontal semicircular canals sense yaw rotations with high-pass filter dynamics and a time constant (TC) around 5 s, yet the rVOR response shows a longer TC due to a central processing stage, known as velocity storage mechanism (VSM). It is generally assumed that the vertical rVOR behaves similarly to the horizontal one; however, VSM processing of the human vertical rVOR is still to be proven. We investigated the vertical rVOR in eight healthy human subjects using three experimental paradigms: (1) per- and post-rotatory around an earth-vertical axis (ear down rotations, EDR), (2) post-rotatory around an earth-horizontal axis with different stopping positions (static otolith stimulation), (3) per-rotatory around an earth-horizontal axis (dynamic otolith stimulation). We found that the TC of vertical rVOR responses ranged 3–10 s, depending both on gravity and on the direction of rotation. The shortest TC were found in response to post-rotatory earth-horizontal stimulation averaging 3.6 s, while they were prolonged in EDR stimulation, i.e. when the head angular velocity vector is aligned with gravity, with a mean value of about 6.0 s. Overall, the longest TC were observed in per-rotatory earth-horizontal stimulation, averaging 7.8 s. The finding of longer TC in EDR than in post-rotatory earth-horizontal stimulation indicates a role for the VSM in the vertical rVOR, although its contribution appears to be weaker than on the horizontal rVOR and may be directionally asymmetric. The results from per-rotatory earth-horizontal stimulation, instead, imply a role for the otoliths in controlling the duration of the vertical rVOR response. We found no reorientation of the response toward earth horizontal, indicating a difference between human and monkey rVOR.