Fast component threshold for vestibular nystagmus in the rabbit

Behavioural characteristics of the quick phase of vestibular nystagmus before and after unilateral labyrinthectomy in guinea pig

The aim of this paper was to characterise the conditions under which the quick phase of vestibular nystagmus is generated in response to sinusoidal horizontal angular accelerations in guinea pig and to determine whether the characteristics of the quick phase are altered following unilateral vestibular deafferentation (UVD). In experiment 1, the quick-phase response to 2-Hz sinusoidal stimuli with different peak head velocities was measured before and after UVD. In experiment 2, lower-frequency stimuli with a fixed amplitude (+/-20 degrees ) were used to measure the eye-movement response. In experiment 1, at 2 Hz, the most noticeable difference between UVD animals and normal animals was a reduction in the number of quick phases generated, particularly when rotating towards the lesioned side: the onset of the quick phase was delayed and occurred at a lower value of peak head velocity compared to normals. However, both these measures probably reflect the depressed slow-phase eye-velocity gain rather than a change in the quick-phase mechanism itself, because if a quick phase was generated there was no difference between UVDs and normals on a variety of measures (duration, position, peak eye velocity) for a 2-Hz stimulus. For both UVD and normal animals there did appear to be a position threshold for the onset of a quick-phase eye movement (approximately +/-7.5 degrees ), although it should be noted that the threshold is not an absolute value. In experiment 2, with lower-frequency stimuli, the characteristics of the quick phase itself were altered in UVD animals. At these lower accelerations, although the head velocity and average eye position for the onset of the quick phase did not differ between UVD and normal animals, there were significant differences between UVD and normal animals in the number of quick phases generated (fewer), the duration of the quick phase (longer) and the peak eye velocity of the quick phase (slower). For lower-frequency stimuli there was no evidence of a specific eye-position threshold for the generation of a quick phase, although the position at which a quick phase occurred rarely exceeded the +/-7.5 degrees value obtained in experiment 1. The behavioural data were used to produce a biologically based neural-network simulation of both the slow- and quick-phase components of the vestibulo-ocular reflex, the results of which are presented in a companion paper.

Contemporary vestibular function testing: accomplishments and future perspectives

The development of a standard test battery for the evaluation of vestibular function required a variety of preliminary investigations about the technical and physiologic foundations of the tests. The most important technologic development was the creation of computerized methods, including hardware and software capabilities. The designs of tests were based on physiologic and diagnostic considerations, as demonstrated in experiments on normal subjects and patients. Although time tested and sound, the available test battery satisfies only a limited number of requirements for comprehensive evaluation of vestibular function. This article describes the list of accomplishments, the state of the present limitations, and the needs for the future.

Maturation of the fast component of vestibular nystagmus during childhood and young adulthood

Primary nystagmus was evoked by constant angular acceleration at near-threshold levels (0.2, 0.4, and 0.6 degree/s2) in 34 normal human subjects (25 children aged 2-11 years and 9 young adults aged 17-21 years). Acceleration was carried out in complete darkness, and with subjects' eyes open. Analysis of response latencies showed that all subjects responded to acceleration magnitude as low as 0.2 degrees/s2. A decrease in response latency was associated with an increase in acceleration magnitude, and there was no significant effect of age on response latency or its relationship to acceleration. However, a relationship was found between age and the percentage of trials showing the presence of a set of three successive beats during acceleration: a significant increase in the frequency of such trials occurred with increasing age. The relationship of these findings to brainstem vestibular modulatory mechanisms is discussed.