Effects of the BalanCI on Working Memory and Balance in Children and Young Adults With Cochleovestibular Dysfunction.

OBJECTIVES: This study aimed to: (1) determine the interaction between cognitive load and balance in children and young adults with bilateral cochleovestibular dysfunction who use bilateral cochlear implants (CIs) and (2) determine the effect of an auditory balance prosthesis (the BalanCI) on this interaction. Many (20 to 70%) children with sensorineural hearing loss experience some degree of vestibular loss, leading to poorer balance. Poor balance could have effects on cognitive resource allocation which might be alleviated by the BalanCI as it translates head-referenced cues into electrical pulses delivered through the CI. It is hypothesized that children and young adults with cochleovestibular dysfunction will demonstrate greater dual-task costs than typically-developing children during dual balance-cognition tasks, and that BalanCI use will improve performance on these tasks. DESIGN: Study participants were 15 typically-developing children (control group: mean age ± SD = 13.6 ± 2.75 years, 6 females) and 10 children and young adults who use bilateral CIs and have vestibular dysfunction (CI-V group: mean age ± SD=20.6 ± 5.36 years, 7 females). Participants completed two working memory tasks (backward auditory verbal digit span task and backward visuospatial dot matrix task) during three balance conditions: seated, standing in tandem stance with the BalanCI off, and standing in tandem stance with the BalanCI on. Working memory performance was quantified as total number of correct trials achieved. Postural stability was quantified as translational and rotational path length of motion capture markers worn on the head, upper body, pelvis, and feet, normalized by trial time. RESULTS: Relative to the control group, children and young adults in the CI-V group exhibited poorer overall working memory across all balance conditions ( p = 0.03), poorer translational postural stability (larger translational path length) during both verbal and visuospatial working memory tasks ( p < 0.001), and poorer rotational stability (larger rotational path length) during the verbal working memory task ( p = 0.026). The CI-V group also exhibited poorer translational ( p = 0.004) and rotational ( p < 0.001) postural stability during the backward verbal digit span task than backward visuospatial dot matrix task; BalanCI use reduced this stability difference between verbal and visuospatial working memory tasks for translational stability overall ( p > 0.9), as well as for rotational stability during the maximum working memory span (highest load) participants achieved in each task ( p = 0.91). CONCLUSIONS: Balance and working memory were impaired in the CI-V group compared with the control group. The BalanCI offered subtle improvements in stability in the CI-V group during a backward verbal working memory task, without producing a negative effect on working memory outcomes. This study supports the feasibility of the BalanCI as a balance prosthesis for individuals with cochleovestibular impairments.

Evaluating the use of a balance prosthesis during balance perturbations in children and young adults with cochleovestibular dysfunction.

Study objectives were to: (1) quantify stability in children and young adults using cochlear implants with concurrent cochleovestibular dysfunction (CI-V) during balance perturbations and (2) to assess effects of an auditory head-referencing device (BalanCI) on their stability. The BalanCI provides auditory feedback via cochlear implants to cue posture and potentially avoid falling in children with CI-V. It was hypothesized that children and young adults with CI-V respond with larger movements to floor perturbations than typically-developing peers (controls) and that BalanCI use decreases these movements. Motion in response to treadmill perturbations was captured by markers on the head, torso, and feet in eight CI-V and 15 control participants. Stability (area under the curve of motion displacement) and peak displacement latencies were measured. The CI-V group demonstrated less stability and slower responses than the control group during medium and large backwards perturbations (p's < 0.01). In the CI-V group, BalanCI use improved stability during large backwards perturbations (p < 0.001), but worsened stability during large sideways perturbations (p's < 0.001). Children and young adults with CI-V move more to remain upright during perturbations than typically-developing peers. The BalanCI has potential to aid physical/vestibular therapy in children with CIs who have poor balance.

Effects of earth-fixed vs head-fixed targets on static ocular counterroll.

OBJECTIVE: To investigate whether static ocular counterroll (OCR) gain is reduced during viewing of an earth-fixed vs a head-fixed target. METHODS: Twelve healthy individuals were recruited. The target consisted of a red fixation cross against a grid pattern at a viewing distance of 33 cm. The target was mounted on a wall (earth fixed) or was coupled to the head (head fixed). Changes in mean torsional eye position were plotted as a function of head position steps (0 degrees +/- 25 degrees in 5 degrees steps), and sigmoidal fits were performed. Mean static OCR gain was calculated by taking the derivative of the fitted functions. RESULTS: Mean static OCR gain was 40% lower with a head-fixed target (-0.084) than with an earth-fixed target (-0.141) (P < .001). CONCLUSION: The reduction in static OCR gain during viewing of a head-fixed target indicates that static OCR is partially negated when a target moves with the head.

The linear vestibulo-ocular reflex in patients with skew deviation.

PURPOSE: The linear vestibulo-ocular reflex (LVOR) is mediated primarily by the otolith organs in the inner ear. Skew deviation is a vertical strabismus believed to be caused by imbalance of otolithic projections to ocular motor neurons (disynaptically through the medial longitudinal fasciculus in the brain stem or polysynaptically through the cerebellum). The authors postulated that if skew deviation is indeed caused by damage to these projections, patients with skew deviation would show abnormal LVOR responses. METHODS: Six patients with skew deviation caused by brain stem or cerebellar lesions and 10 healthy subjects were recruited. All subjects underwent brief, sudden, interaural translations of the head (head heaves) using a head-sled device at an average peak acceleration of 0.42g (range, 0.1-1.1g) while continuously viewing an earth-fixed target monocularly at 15 and 20 cm. LVOR sensitivity (peak rotational eye velocity to peak linear head velocity) and velocity gain (peak actual-to-ideal rotational eye velocities) were calculated for the responses within the first 100 ms after onset of head movements. RESULTS: LVOR sensitivities and velocity gains in patients were decreased by 56% to 62% in both eyes compared with healthy subjects. This binocular reduction in LVOR responses was asymmetric--the magnitude of reduction differed between eyes by 37% to 143% for sensitivities and by 36% to 94% for velocity gains. There were no differences in response between right and left heaves. CONCLUSIONS: The binocular, asymmetric reduction in LVOR sensitivity and velocity gain provides support that imbalance in the otolith-ocular pathway is a mechanism of skew deviation.

Effects of age, viewing distance and target complexity on static ocular counterroll.

The ocular counterroll (OCR) reflex generates partially compensatory torsional eye movements during static head roll tilt. We assessed the influence of age, viewing distance and target complexity on the OCR across the age span (13-63 years; n=47), by recording eye movements during head-on-body roll tilt (0+/-40 degrees in 5 degrees steps) while subjects viewed simple vs. complex targets at 0.33 and 1m. We found that subjects > or = 31 years had lower gains than those < or =30 years, but only for far targets. Consistent with prior reports, far targets elicited higher OCR gains than near targets, and target complexity had no effect on gains, suggesting that visual input is primarily used to maintain vergence during OCR.