title: Velocity storage in the human vertical rotational vestibulo-ocular reflex.
abstract: 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.
authors.affiliation: Department of Computer and Systems Science, University of Pavia, Pavia, Italy.
authors.forename: G
authors.initials: G
authors.lastname: Bertolini
authors.forename: S
authors.initials: S
authors.lastname: Ramat
mesh_terms: D000328:Adult; D001921:Brain / Q000502:physiology; D005260:Female; D005403:Fixation, Ocular / Q000502:physiology; D018466:Gravity Sensing / Q000502:physiology*; D019416:Head Movements / Q000502:physiology; D006801:Humans; D008297:Male; D008875:Middle Aged; D009039:Motion Perception / Q000502:physiology*; D017120:Nystagmus, Optokinetic / Q000502:physiology; D010037:Otolithic Membrane / Q000502:physiology; D004856:Postural Balance / Q000502:physiology*; D011930:Reaction Time / Q000502:physiology; D012027:Reflex, Vestibulo-Ocular / Q000502:physiology*; D012212:Rheology / Q000379:methods; D012399:Rotation / Q000009:adverse effects; D012444:Saccule and Utricle / Q000502:physiology*; D012665:Semicircular Canals / Q000502:physiology*