Journal of Vestibular Research

Vestibulo-ocular and second-order neurons in medial and superior vestibular nuclei of alert cats were identified by antidromic and orthodromic electrical stimulation, and their responses to whole body rotations were recorded in the dark. Neurons that had spatial sensitivity most closely aligned with the anterior canal (anterior canal neurons) were compared with neurons that had spatial sensitivity most closely aligned with the posterior canal (posterior canal neurons). Responses were recorded during low frequency earth-horizontal axis pitch rotations in the normal upright posture, and during earth-vertical axis pitch with the head and body lying on the left side. During upright pitch, response phases of anterior canal neurons slightly lagged those of posterior canal neurons or primary vestibular afferents, as previously reported. During on-side pitch, anterior canal neurons showed far greater phase leads with respect to head velocity than posterior canal neurons, primary vestibular afferents, or previously reported vestibulo-ocular reflex eye movements. These results provide challenges for vestibulo-ocular reflex models to incorporate central mechanisms for phase leads among the inputs to anterior canal neurons and to explain how the anterior canal neuron signals reported here combine with other signals to produce observed vestibulo-ocular reflex behavior.

This study compares the children and adult response to a novel postural challenge. One group of children (n=13, age 7–9) and one adult reference group (n=12 age 15–32) were subjected to vibration induced body sway and posturography with both open and closed eyes for 5 consecutive days. There was a gradual decrease of induced body sway over time in both groups (p< 0.001) between the subsequent trials, but only in the adult group was there a reduction of induced body sway over time within each trial (p< 0.05). The children had on a considerably less level of induced body sway when they started the second trial than they finished the first (p< 0.01). There appears to be a different approach of adaptation to a new postural challenge between children and adults.

The effects of stimulus eccentricity, visual angle, and fixation on linear vection (sensation of self-translation induced by large moving scenes) were examined in healthy young people. Three aspects of vection were measured: latency, total vection time, and strength. The results showed that when peripheral and central stimuli are equal in area, they induce similar vection, but only when they are presented with a fixation cross. When presented without a fixation cross, peripheral stimuli are more effective in inducing vection than central stimuli. In addition, central stimuli with a fixation cross elicited more vection than central stimuli without a fixation cross. Fixation had no influence on the vection induced by peripheral stimuli. These findings indicate that statements about the role of central and peripheral stimuli of equal area in inducing vection should be made only in conjunction with reports about whether these stimuli are presented with or without fixation.

Numerous attempts have been made to find physiological parameters that might predict susceptibility to seasickness. However, to date, no physiological index has been found that can serve as a diagnostic tool for individual susceptibility to motion sickness at the personnel selection stage. A number of studies have demonstrated that linear acceleration in the vertical plane is the most provocative stimulus of motion sickness. The main physiological sensory modality responsible for monitoring vertical acceleration is the saccule. Over the last decade, vestibular evoked myogenic potentials (VEMP) have come to be recognized as a reliable procedure for the evaluation of saccular function. We used the VEMP test to assess otolith responses in 15 seasickness-susceptible (SS) and 15 non-seasickness-susceptible (NSS) healthy male crew members. The SS group exhibited a significantly higher VEMP threshold and a significantly lower peak-to-peak p13-n23 amplitude interval compared with the NSS group. Further analysis by logistic regression found threshold to be the dominant factor associated with seasickness susceptibility. The study demonstrated differences in the VEMP reflex of the SS and NSS groups. The threshold difference may represent an intrinsic mechanistic difference between the vestibular systems of the two groups. Theoretically, increased susceptibility to seasickness may be due to a discrepancy between the various neural systems as a result of reduced otolith responses.

Patients with unilateral vestibular deficit (UVD) report difficulties with maintaining balance while executing fast head turns. Our aim was to determine whether head, trunk, and pelvis angular displacements were symmetrical in patients with UVD as they executed voluntary yaw rotation of the head towards or away from the side of the vestibular lesion, during standing and walking. Eight patients who underwent surgical resection of an acoustic neuroma stood with feet together or walked at comfortable pace across a 10-meter walkway. They turned the head as quickly and as fast as possible in the direction indicated by an illuminating arrow (left, right or none). The head angular displacement was similar towards the affected and intact sides. Acceleration tended to be larger during head rotations towards the affected versus the intact side by 13% at the head, 42% at the trunk and 37% at the pelvis (p> 0.05, NS). The pelvis rotated opposite to the head in 65% of trials towards the affected side and 56% of the trials towards the intact side during standing and 81% and 69%, respectively during walking. Overall, the UVD had only a minor influence on the symmetry of head, trunk and pelvis kinematics during fast yaw rotation of the head executed during standing and walking.

The recruitment of extra-vestibular mechanisms to assist a deficient angular vestibulo-ocular reflex (aVOR) during ipsilesional head rotations is well established and includes saccades of reduced latency that occur in the direction of the lesioned aVOR, termed compensatory saccades (CS). Less well known is the functional relevance of these unique saccades. Here we report a 42 y.o. male diagnosed with right unilateral vestibular hypofunction due to vestibular neuronitis who underwent a vestibular rehabilitation program including gaze stabilization exercises. After three weeks, he had a significant improvement in his ability to see clearly during head rotation. Our data show a reduction in the recruitment and magnitude of CS as well as improved peripheral aVOR gain (eye velocity/head velocity) and retinal eye velocity. Our data suggest an inverse, dynamic relationship between the recruitment of CS and the gain of the aVOR.