Adaptation of VOR to Coriolis Stimulation

• Published in: Annals of the New York Academy of Sciences 2005-04, Vol.1039 (1), p.88-96
• Main Authors: ADENOT, SOPHIE, JARCHOW, THOMAS, YOUNG, LAURENCE R.
• Format: Article
• Language: English
• Subjects: Acclimatization; Adaptation; Adolescent; Adult; Amplitudes; Angular velocity; Coriolis cross-coupling stimulus; Decay; Eye Protective Devices; Female; Head movement; Head Movements - physiology; Humans; Male; Matlab; nystagmus; Nystagmus, Physiologic; Photic Stimulation; Reflex, Vestibulo-Ocular - physiology; Rotation; Software; Supine Position; Time constant; Transient responses; vestibulo-ocular reflex
• ISSN: 0077-8923; 1749-6632
• DOI: 10.1196/annals.1325.009

: The vestibulo‐ocular reflex (VOR) is normally characterized by the gain and phase of slow‐phase velocity (SPV) relative to the stimulus velocity. Although this is perfectly satisfactory for steady‐state sinusoidal oscillations about a single axis, it is less useful when applied to transient responses. The well‐known decay of nystagmus following a step change of head velocity approximately follows a double exponential, with an initial amplitude (A), a long time constant (τ), and an adaptation time constant (τa). We have developed a means of representing the transient response for a complex head velocity stimulus as experienced during high‐speed artificial gravity (AG) experiments. When a subject, lying supine on a rotating horizontal platform, makes a yaw head movement of amplitude θ, the vertical semicircular canals experience a step in angular velocity. The pitch stimulus is equal to the change in the component of the centrifuge angular velocity (ωc) aligned with the interaural axis, and gives rise to a vertical VOR. The magnitude of the step change is ωc sin θ. The SPV is approximated by an exponential decay of amplitude A and single time constant τ, and then normalized relative to this stimulus step. MATLAB scripts filter the raw eye position data to remove noise, blinks, and saccades, differentiate the signal, and remove fast phases to obtain SPV. The amplitude of the fitted SPV exponential is divided by ωc sin θ to obtain the normalized SPV. A and τ are shown to behave differently as subjects adapt to repeated head movements of different amplitudes.