Search

Rapid head movement was combined with continuous caloric irrigation of the external ear to evaluate the time courses of the on-step (null-to-supine repositioning) and off-step (supine-to-null repositioning) vestibulo-ocular reflexes (VOR) responses in eight healthy subjects. During continuous air-caloric irrigation, each subject's head was positioned with his/her lateral semicircular canal alternately placed in the null (horizontal) and activating (vertical) planes, and the time course of the slow phase eye velocity was evaluated. The resulting responses were characterized by estimates of activation and adaptation components, and their amplitudes and time constants were calculated. Comparisons of the on-step and off-step responses revealed the activation and adaptation components of the VOR to have similar amplitudes. On the other hand, the time constant for the activation component was prolonged for the off-step response, while that for the adaptation component was shortened. Null-to-supine and reciprocal vestibular stimulation during continuous caloric irrigation of the external ear canal elicited asymmetric VOR responses that exhibited differing time courses. [ABSTRACT FROM AUTHOR]

In response to translations of the head, the linear vestibulo-ocular reflex (LVOR) produces compensatory eye movements that are high-pass in nature, with a declining response magnitude and an increasing phase lead with declining stimulus frequency. Perception of head translation, however, is reported to be robust at much lower frequency than predicted by the LVOR, causing speculation that the vestibular processing underlying reflex and perceptual responses are different. Direct comparison of these two responses across a large frequency range proves problematic, in part because of difficulties encountered in the assessment of perception at high frequency, and confounding variables at low frequency. We used innovative techniques to measure psychophysical responses to translation, and find strong similarity to the LVOR. These include experiments in which motion cues were limited to those of an inertial nature, and conclude that the vestibular system comprises only one input to perceptual mechanisms related to linear motion, and this is supplemented (particularly at low frequency) by somatic and cognitive cues. [ABSTRACT FROM AUTHOR]

Dizziness and vertigo are some of the more frequently encountered symptoms in neurology clinics. In turn, one of the most common causes of vertigo is benign paroxysmal positional vertigo (BPPV), accounting for a quarter of all patients with dizziness and vertigo. Reviewing the value of the positional manoeuvres available is relevant, particularly in the light of the efficient treatments available for BPPV. In this article I will deal with positional manoeuvres first, and then with how vestibulo-ocular reflexes (VOR) can be tested in the clinic. I will not discuss VOR suppression assessment. [ABSTRACT FROM AUTHOR]