Generalization of vestibular learning to earth-fixed targets is possible but limited when the polarity of afferent vestibular information is changed

Vestibular perceptual testing from lab to clinic: a review

Not all dizziness presents as vertigo, suggesting other perceptual symptoms for individuals with vestibular disease. These non-specific perceptual complaints of dizziness have led to a recent resurgence in literature examining vestibular perceptual testing with the aim to enhance clinical diagnostics and therapeutics. Recent evidence supports incorporating rehabilitation methods to retrain vestibular perception. This review describes the current field of vestibular perceptual testing from scientific laboratory techniques that may not be clinic friendly to some low-tech options that may be more clinic friendly. Limitations are highlighted suggesting directions for additional research.

Association between vestibular function and rotational spatial orientation perception in older adults

BACKGROUND

Spatial orientation is a complex process involving vestibular sensory input and possibly cognitive ability. Previous research demonstrated that rotational spatial orientation was worse for individuals with profound bilateral vestibular dysfunction.

OBJECTIVE

Determine whether rotational and linear vestibular function were independently associated with large amplitude rotational spatial orientation perception in healthy aging.

METHODS

Tests of rotational spatial orientation accuracy and vestibular function [vestibulo-ocular reflex (VOR), ocular and cervical vestibular evoked myogenic potentials (VEMP)] were administered to 272 healthy community-dwelling adults participating in the Baltimore Longitudinal Study of Aging. Using a mixed model multiple linear regression we regressed spatial orientation errors on lateral semicircular canal function, utricular function (ocular VEMP), and saccular function (cervical VEMP) in a single model controlling for rotation size, age, and sex.

RESULTS

After adjusting for age, and sex, individuals with bilaterally low VOR gain (β= 20.9, p = 0.014) and those with bilaterally absent utricular function (β= 9.32, p = 0.017) made significantly larger spatial orientation errors relative to individuals with normal vestibular function.

CONCLUSIONS

The current results demonstrate for the first time that either bilateral lateral semicircular canal dysfunction or bilateral utricular dysfunction are associated with worse rotational spatial orientation. We also demonstrated in a healthy aging cohort that increased age also contributes to spatial orientation ability.

Two Neural Circuits to Point Towards Home Position After Passive Body Displacements

A challenge in motor control research is to understand the mechanisms underlying the transformation of sensory information into arm motor commands. Here, we investigated these transformation mechanisms for movements whose targets were defined by information issued from body rotations in the dark (i.e., idiothetic information). Immediately after being rotated, participants reproduced the amplitude of their perceived rotation using their arm (Experiment 1). The cortical activation during movement planning was analyzed using electroencephalography and source analyses. Task-related activities were found in regions of interest (ROIs) located in the prefrontal cortex (PFC), dorsal premotor cortex, dorsal region of the anterior cingulate cortex (ACC) and the sensorimotor cortex. Importantly, critical regions for the cognitive encoding of space did not show significant task-related activities. These results suggest that arm movements were planned using a sensorimotor-type of spatial representation. However, when a 8 s delay was introduced between body rotation and the arm movement (Experiment 2), we found that areas involved in the cognitive encoding of space [e.g., ventral premotor cortex (vPM), rostral ACC, inferior and superior posterior parietal cortex (PPC)] showed task-related activities. Overall, our results suggest that the use of a cognitive-type of representation for planning arm movement after body motion is necessary when relevant spatial information must be stored before triggering the movement.

Learning to use vestibular sense for spatial updating is context dependent

As we move, perceptual stability is crucial to successfully interact with our environment. Notably, the brain must update the locations of objects in space using extra-retinal signals. The vestibular system is a strong candidate as a source of information for spatial updating as it senses head motion. The ability to use this cue is not innate but must be learned. To date, the mechanisms of vestibular spatial updating generalization are unknown or at least controversial. In this paper we examine generalization patterns within and between different conditions of vestibular spatial updating. Participants were asked to update the position of a remembered target following (offline) or during (online) passive body rotation. After being trained on a single spatial target position within a given task, we tested generalization of performance for different spatial targets and an unpracticed spatial updating task. The results demonstrated different patterns of generalization across the workspace depending on the task. Further, no transfer was observed from the practiced to the unpracticed task. We found that the type of mechanism involved during learning governs generalization. These findings provide new knowledge about how the brain uses vestibular information to preserve its spatial updating ability.

Improving spatial updating accuracy in absence of external feedback

Updating the position of an earth-fixed target during whole-body rotation seems to rely on cognitive processes such as the utilization of external feedback. According to perceptual learning models, improvement in performance can also occur without external feedback. The aim of this study was to assess spatial updating improvement in the absence and in the presence of external feedback. While being rotated counterclockwise (CCW), participants had to predict when their body midline had crossed the position of a memorized target. Four experimental conditions were tested: (1) Pre-test: the target was presented 30° in the CCW direction from participant's midline. (2) Practice: the target was located 45° in the CCW direction from participant's midline. One group received external feedback about their spatial accuracy (Mackrous and Simoneau, 2014) while the other group did not. (3) Transfer T(30)CCW: the target was presented 30° in the CCW direction to evaluate whether improvement in performance, during practice, generalized to other target eccentricity. (4) Transfer T(30)CW: the target was presented 30° in the clockwise (CW) direction and participants were rotated CW. This transfer condition evaluated whether improvement in performance generalized to the untrained rotation direction. With practice, performance improved in the absence of external feedback (p=0.004). Nonetheless, larger improvement occurred when external feedback was provided (ps=0.002). During T(30)CCW, performance remained better for the feedback than the no-feedback group (p=0.005). However, no group difference was observed for the untrained direction (p=0.22). We demonstrated that spatial updating improved without external feedback but less than when external feedback was given. These observations are explained by a mixture of calibration processes and supervised vestibular learning.