Vestibular contributions to high-level sensorimotor functions

Postural imbalance without visual input is associated with specific neuropsychological deficits in older adults - results from the LIFE-adult study

Introduction

Modifiable risk factors play an important role in preventing dementia and reducing its progression. Regular physical activity already in midlife, which relies on intact multisensory balance control, can help to decrease the risk of dementia. However, our understanding of the relationship between postural balance and cognitive functions remains limited. The objective of our study was to investigate the association of postural balance during different sensory conditions with specific cognitive domains in older adults.

Methods

Participants were from the population-based prospective "Leipzig Research Center for Civilization Diseases" (LIFE-Adult) cohort in Leipzig, Germany. Executive, memory and processing speed functions were tested by the Consortium to Establish a Registry for Alzheimer's disease (CERAD) plus battery. Assessment of visuospatial abilities was based on the short form of the Judgment of Line Orientation Test (JLO). Postural sway was recorded on a force plate with eyes open and closed. Romberg's ratios were calculated for sway path and sway area as a proxy for balance without visual control and tested in generalized linear regression models with the summary scores of executive function, memory, processing speed and visuospatial function as dependent variables. All models were adjusted for sex, age, ApoE status, socioeconomic status, anamnestic stroke, and diabetes.

Results

In total, we analyzed 460 participants with a mean age of 68.6 years, range 60 to 80, 47.6% female. A higher Romberg's ratio for sway area was a significant indicator for impaired visuospatial abilities as measured by the dichotomized JLO (Odds Ratio = 1.42, 95% confidence interval 1.07 to 1.88). Romberg's ratios were not significantly associated with executive functions, procedural speed or memory functions.

Discussion

It may be worthwhile to examine in the future whether inclusion of balance testing enhances the value of screening programs for cognitive impairment. Inversely, it may be appropriate to apply routine cognitive tests when balance problems are detected in older patients.

Visually-Induced Motor Imagery Effects on Motor Adaptation to Reverse Steering Cycling. A Randomized Controlled Trial

Purpose: First, testing an intervention of neuromodulation based on motor imagery and action observation as a promoter of motor adaptation of a complex motor task involving balance. Second, determining what prior balance factors can affect the motor adaptation task. Methods: A double-blind randomized controlled trial was performed. Forty-eight healthy subjects were recruited. The balance of all participants during gait and standing was assessed before adapting to the complex, multi-limb motor task of riding an inverse steering bicycle (ISB). Two interventions were carried out interleaved among trials of adaptation to the motor task: the experimental group (n = 24) was asked to perform neuromodulation (EN) by watching first-person ISB riding through immersive VR glasses and, simultaneously, mentally mimicking the movements. The control group (CG) was asked to watch a slideshow video of steady landscape images. Results: The results showed that the EN group did not improve the motor adaptation rate and induced higher adaptation times with respect to the CG. However, while the motor adaptation success showed a significant dependence on the prior proprioceptive participation in balance in the CG, the EN group did not present any relationship between the prior balance profile and motor adaptation outcome. Conclusions: Results point to a benefit of the visually guided neuromodulation for the motor adaptation of the subjects with low participation of proprioception in balance. Moreover, the results from the control group would allow to disclose prognostic factors about the success of the motor adaptation, and also prescription criteria for the proposed neuromodulation based on the balance profile.

Continuous peripersonal tracking accuracy is limited by the speed and phase of locomotion

Recent evidence suggests that perceptual and cognitive functions are codetermined by rhythmic bodily states. Prior investigations have focused on the cardiac and respiratory rhythms, both of which are also known to synchronise with locomotion-arguably our most common and natural of voluntary behaviours. Compared to the cardiorespiratory rhythms, walking is easier to voluntarily control, enabling a test of how natural and voluntary rhythmic action may affect sensory function. Here we show that the speed and phase of human locomotion constrains sensorimotor performance. We used a continuous visuo-motor tracking task in a wireless, body-tracking virtual environment, and found that the accuracy and reaction time of continuous reaching movements were decreased at slower walking speeds, and rhythmically modulated according to the phases of the step-cycle. Decreased accuracy when walking at slow speeds suggests an advantage for interlimb coordination at normal walking speeds, in contrast to previous research on dual-task walking and reach-to-grasp movements. Phasic modulations of reach precision within the step-cycle also suggest that the upper limbs are affected by the ballistic demands of motor-preparation during natural locomotion. Together these results show that the natural phases of human locomotion impose constraints on sensorimotor function and demonstrate the value of examining dynamic and natural behaviour in contrast to the traditional and static methods of psychological science.

Reactive Agility and Pitching Performance Improvement in Visually Impaired Competitive Italian Baseball Players: An Innovative Training and Evaluation Proposal

Visual input significantly affects kinesthesis skills and, hence, visually impaired individuals show less developed sensorimotor control, especially in an unfamiliar outdoor environment. Regular blind baseball practice can counteract such a deficit but, given the complex kinetic chain model required, a targeted workout proposal is needed to improve the main athletic gesture performance. On these premises, we investigated, for the first time, the running and pitching performance of a competitive Italian blind baseball team through quantitative tools and parameters such as Libra Easytech sensorized proprioceptive board, goniometric active range of motion, chronometric speed, and pitching linear length. Moreover, the perceived physical exertion was assessed by the Borg CR10 scale. Consequently, an adapted athletic training protocol was designed and tested on the field during the competitive season, with the aim to strengthen sport specific-gesture coordination and efficacy as well as to prevent injuries. Quantitative assessments showed an improvement in ankle stability index, bilateral upper limb and hip mobility, reactive agility, running braking phase control during second base approaching, and auditory target-related pitching accuracy along with a decrease in perceived physical exertion. This protocol might therefore represent an effective and easily reproducible training and evaluation approach to tailor management of visually impaired baseball players, and safely improve their athletic performance under the supervision of an adapted exercise specialist.

Predictive steering: integration of artificial motor signals in self-motion estimation

The brain's computations for active and passive self-motion estimation can be unified with a single model that optimally combines vestibular and visual signals with sensory predictions based on efference copies. It is unknown whether this theoretical framework also applies to the integration of artificial motor signals, such as those that occur when driving a car, or whether self-motion estimation in this situation relies on sole feedback control. Here, we examined if training humans to control a self-motion platform leads to the construction of an accurate internal model of the mapping between the steering movement and the vestibular reafference. Participants (n = 15) sat on a linear motion platform and actively controlled the platform's velocity using a steering wheel to translate their body to a memorized visual target (motion condition). We compared their steering behavior to that of participants (n = 15) who remained stationary and instead aligned a nonvisible line with the target (stationary condition). To probe learning, the gain between the steering wheel angle and the platform or line velocity changed abruptly twice during the experiment. These gain changes were virtually undetectable in the displacement error in the motion condition, whereas clear deviations were observed in the stationary condition, showing that participants in the motion condition made within-trial changes to their steering behavior. We conclude that vestibular feedback allows not only the online control of steering but also a rapid adaptation to the gain changes to update the brain's internal model of the mapping between the steering movement and the vestibular reafference.NEW & NOTEWORTHY Perception of self-motion is known to depend on the integration of sensory signals and, when the motion is self-generated, the predicted sensory reafference based on motor efference copies. Here we show, using a closed-loop steering experiment with a direct coupling between the steering movement and the vestibular self-motion feedback, that humans are also able to integrate artificial motor signals, like the motor signals that occur when driving a car.

Visuospatial Cognitive Dysfunction in Patients with Vestibular Loss

OBJECTIVE

To characterize visuospatial and nonvisuospatial cognitive domains affected by vestibular loss and determine whether patient-reported outcomes measures (PROMs) correlate with performance on neuropsychological tests.

STUDY DESIGN

Cross-sectional study.

SETTING

University-based tertiary medical center.

PATIENTS

Sixty-nine age-matched subjects: 25 patients with bilateral vestibular loss (BVL), 14 patients with unilateral vestibular loss (UVL), and 30 normal controls (NC).

INTERVENTIONS

Neuropsychological tests used to assess visuospatial and auditory short-term and working memory, number magnitude representation, executive function, and attention. Validated PROMs used to evaluate quality of life and subjective cognitive impairment.

MAIN OUTCOME MEASURES

Performance on neuropsychological tests and scores on PROM surveys.

RESULTS

BVL and UVL patients performed significantly worse than NC subjects on tasks requiring visuospatial representation compared with NC subjects ( p < 0.01). BVL patients demonstrated decreased performance on spatial representation tasks compared with UVL and NC subjects ( p < 0.05 and p < 0.05, respectively). All subject groups performed similarly on tasks assessing nonvisuospatial cognitive domains, such as auditory short-term and working memory, executive function, and attention. PROMs did not seem to correlate with performance on neuropsychological tasks.

CONCLUSION

Patients with vestibular loss exhibit impairments in tasks requiring visuospatial representation but perform similarly to NC subjects in tasks of auditory working memory, executive function, or attention. Currently available questionnaires may be insufficient to screen patients for cognitive deficits.

On the Dynamics of Spatial Updating

Most of our knowledge on the human neural bases of spatial updating comes from functional magnetic resonance imaging (fMRI) studies in which recumbent participants moved in virtual environments. As a result, little is known about the dynamic of spatial updating during real body motion. Here, we exploited the high temporal resolution of electroencephalography (EEG) to investigate the dynamics of cortical activation in a spatial updating task where participants had to remember their initial orientation while they were passively rotated about their vertical axis in the dark. After the rotations, the participants pointed toward their initial orientation. We contrasted the EEG signals with those recorded in a control condition in which participants had no cognitive task to perform during body rotations. We found that the amplitude of the P₁N₁ complex of the rotation-evoked potential (RotEPs) (recorded over the vertex) was significantly greater in the Updating task. The analyses of the cortical current in the source space revealed that the main significant task-related cortical activities started during the N₁P₂ interval (136–303 ms after rotation onset). They were essentially localized in the temporal and frontal (supplementary motor complex, dorsolateral prefrontal cortex, anterior prefrontal cortex) regions. During this time-window, the right superior posterior parietal cortex (PPC) also showed significant task-related activities. The increased activation of the PPC became bilateral over the P₂N₂ component (303–470 ms after rotation onset). In this late interval, the cuneus and precuneus started to show significant task-related activities. Together, the present results are consistent with the general scheme that the first task-related cortical activities during spatial updating are related to the encoding of spatial goals and to the storing of spatial information in working memory. These activities would precede those involved in higher order processes also relevant for updating body orientation during rotations linked to the egocentric and visual representations of the environment.

Watching the Effects of Gravity. Vestibular Cortex and the Neural Representation of "Visual" Gravity

Gravity is a physical constraint all terrestrial species have adapted to through evolution. Indeed, gravity effects are taken into account in many forms of interaction with the environment, from the seemingly simple task of maintaining balance to the complex motor skills performed by athletes and dancers. Graviceptors, primarily located in the vestibular otolith organs, feed the Central Nervous System with information related to the gravity acceleration vector. This information is integrated with signals from semicircular canals, vision, and proprioception in an ensemble of interconnected brain areas, including the vestibular nuclei, cerebellum, thalamus, insula, retroinsula, parietal operculum, and temporo-parietal junction, in the so-called vestibular network. Classical views consider this stage of multisensory integration as instrumental to sort out conflicting and/or ambiguous information from the incoming sensory signals. However, there is compelling evidence that it also contributes to an internal representation of gravity effects based on prior experience with the environment. This a priori knowledge could be engaged by various types of information, including sensory signals like the visual ones, which lack a direct correspondence with physical gravity. Indeed, the retinal accelerations elicited by gravitational motion in a visual scene are not invariant, but scale with viewing distance. Moreover, the "visual" gravity vector may not be aligned with physical gravity, as when we watch a scene on a tilted monitor or in weightlessness. This review will discuss experimental evidence from behavioral, neuroimaging (connectomics, fMRI, TMS), and patients' studies, supporting the idea that the internal model estimating the effects of gravity on visual objects is constructed by transforming the vestibular estimates of physical gravity, which are computed in the brainstem and cerebellum, into internalized estimates of virtual gravity, stored in the vestibular cortex. The integration of the internal model of gravity with visual and non-visual signals would take place at multiple levels in the cortex and might involve recurrent connections between early visual areas engaged in the analysis of spatio-temporal features of the visual stimuli and higher visual areas in temporo-parietal-insular regions.

Vestibular status: A missing factor in our understanding of brain reorganization in deaf individuals

The brain of deaf people is definitely not just deaf, and we have to reconsider what we know about the impact of hearing loss on brain development in light of comorbid vestibular impairments.

Balance, gait, and navigation performance are related to physical exercise in blind and visually impaired children and adolescents

Self-motion perception used for locomotion and navigation requires the integration of visual, vestibular, and proprioceptive input. In the absence of vision, postural stability and locomotor tasks become more difficult. Previous research has suggested that in visually deprived children, postural stability and levels of physical activity are overall lower than in sighted controls. Here we hypothesized that visually impaired and blind children and adolescents differ from sighted controls in postural stability and gait parameters, and that physically active individuals outperform sedentary peers in postural stability and gait parameters as well as in navigation performance. Fourteen blind and visually impaired children and adolescents (8-18 years of age) and 14 matched sighted individuals took part. Assessments included postural sway, single-leg stance time, parameters of gait variability and stability, self-reported physical activity, and navigation performance. Postural sway was larger and single-leg stance time was lower in blind and visually impaired participants than in blindfolded sighted individuals. Physical activity was higher in the sighted group. No differences between the group of blind and visually impaired and blindfolded sighted participants were observed for gait parameters and navigation performance. Higher levels of physical activity were related to lower postural sway, longer single-leg stance time, higher gait stability, and superior navigation performance in blind and visually impaired participants. The present data suggest that physical activity may enhance postural stability and gait parameters, and thereby promote navigation performance in blind and visually impaired children and adolescents.

Improved balance performance accompanied by structural plasticity in blind adults after training

Postural control requires the sensory integration of visual, vestibular, and proprioceptive signals. In the absence of vision, either by blindfolding or in blind individuals, balance performance is typically poorer than with sight. Previous research has suggested that despite showing compensatory vestibular and proprioceptive processing during upright standing, balance performance in blind individuals is overall lower than in sighted controls with eyes open. The present study tested whether balance training, which places demands on vestibular and proprioceptive self-motion perception, improves balance performance in blind adults, and whether we find similar structural correlates in cortical and subcortical brain areas as have been reported in sighted individuals. Fourteen congenitally or late blind adults were randomly assigned to either a balance or a relaxation group and exercised twice a week for 12 weeks. Assessments prior to and after training included balance tests and the acquisition of T1-weighted MRI images. The blind balance group significantly improved in dynamic, static, and functional balance performance compared to the blind relaxation group. The balance performance improvement did not differ from that of age- and gender matched sighted adults after balance training. Cortical thickness increased in the left parahippocampus and decreased in the inferior insula bilaterally in the blind balance group compared to the blind relaxation group. Thickness decreases in the insula were related to improved static and functional balance. Gray matter volume was reduced in the left hippocampus proper and increased in the right subiculum in the blind balance group. The present data suggest that impaired balance performance in blind adults can be significantly improved by a training inducing plasticity in brain regions associated with vestibular and proprioceptive self-motion processing.

Relationships Between Accuracy in Predicting Direction of Gravitational Vertical and Academic Performance and Physical Fitness in Schoolchildren

Enhanced levels of cardio-respiratory fitness (CRF) and physical activity (PA) are both positively associated with health and academic outcomes, but less is known about the spatial processing and perceptual components of PA. Perception of vertical (PV) is a spatial orientation ability that is important for PA, and is usually measured as relative accuracy in aligning an object to gravitational vertical against a tilted background. However, evidence is inconclusive regarding the relationship of PV to educational outcomes – most importantly, numeracy. Students were recruited from primary schools in the Australian Capital Territory. A group of 341 (females n = 162, mean age 11.3 years) children performed all the tests required for this study. A computerised rod and frame test of PV employing a small (20°) visual angle was administered, and socio-economic status (SES), national education test results (NAPLAN, 2010), and CRF and PA data were collected. Correlation and hierarchical regression analysis were used to examine the inter-relationships between PV and CRF, PA, SES and NAPLAN results. The two extreme quartile score groups from the measures of PV, PA and CRF were examined in relation to NAPLAN scores. PV scores arising from testing with a small visual angle and SES were found to be significantly associated with overall academic scores, and with the Numeracy, Reading, and Writing components of academic performance. Female gender was significantly associated with Writing score, and male with Numeracy score. Being less influenced by the background tilted frame, and therefore having visual field independence (FI), was associated with significantly higher academic scores, with the largest effect in Numeracy scores (effect size, d = 0.82) and also associated with higher CRF and PA levels. FI was positively associated with all the academic modules examined, and most strongly with Numeracy test results, suggesting that FI provides an indicator of STEM ability. These findings suggest that further longitudinal research into strategies designed to enhance visual FI deserve consideration, with a focus on specialized PA programs for pre-pubescent children. It is possible that small visual angle spatial tasks during PA may stimulate neural networks involved in numerical cognition.

The parieto-insular vestibular cortex in humans: more than a single area?

Here, we review the structure and function of a core region in the vestibular cortex of humans that is located in the midposterior Sylvian fissure and referred to as the parieto-insular vestibular cortex (PIVC). Previous studies have investigated PIVC by using vestibular or visual motion stimuli and have observed activations that were distributed across multiple anatomical structures, including the temporo-parietal junction, retroinsula, parietal operculum, and posterior insula. However, it has remained unclear whether all of these anatomical areas correspond to PIVC and whether PIVC responds to both vestibular and visual stimuli. Recent results suggest that the region that has been referred to as PIVC in previous studies consists of multiple areas with different anatomical correlates and different functional specializations. Specifically, a vestibular but not visual area is located in the parietal operculum, close to the posterior insula, and likely corresponds to the nonhuman primate PIVC, while a visual-vestibular area is located in the retroinsular cortex and is referred to, for historical reasons, as the posterior insular cortex area (PIC). In this article, we review the anatomy, connectivity, and function of PIVC and PIC and propose that the core of the human vestibular cortex consists of at least two separate areas, which we refer to together as PIVC+. We also review the organization in the nonhuman primate brain and show that there are parallels to the proposed organization in humans.

State Estimation for Early Feedback Responses in Reaching: Intramodal or Multimodal?

Humans are highly skilled in controlling their reaching movements, making fast and task-dependent movement corrections to unforeseen perturbations. To guide these corrections, the neural control system requires a continuous, instantaneous estimate of the current state of the arm and body in the world. According to Optimal Feedback Control theory, this estimate is multimodal and constructed based on the integration of forward motor predictions and sensory feedback, such as proprioceptive, visual and vestibular information, modulated by context, and shaped by past experience. But how can a multimodal estimate drive fast movement corrections, given that the involved sensory modalities have different processing delays, different coordinate representations, and different noise levels? We develop the hypothesis that the earliest online movement corrections are based on multiple single modality state estimates rather than one combined multimodal estimate. We review studies that have investigated online multimodal integration for reach control and offer suggestions for experiments to test for the existence of intramodal state estimates. If proven true, the framework of Optimal Feedback Control needs to be extended with a stage of intramodal state estimation, serving to drive short-latency movement corrections.

Task-dependent vestibular feedback responses in reaching

When reaching for an earth-fixed object during self-rotation, the motor system should appropriately integrate vestibular signals and sensory predictions to compensate for the intervening motion and its induced inertial forces. While it is well established that this integration occurs rapidly, it is unknown whether vestibular feedback is specifically processed dependent on the behavioral goal. Here, we studied whether vestibular signals evoke fixed responses with the aim to preserve the hand trajectory in space or are processed more flexibly, correcting trajectories only in task-relevant spatial dimensions. We used galvanic vestibular stimulation to perturb reaching movements toward a narrow or a wide target. Results show that the same vestibular stimulation led to smaller trajectory corrections to the wide than the narrow target. We interpret this reduced compensation as a task-dependent modulation of vestibular feedback responses, tuned to minimally intervene with the task-irrelevant dimension of the reach. These task-dependent vestibular feedback corrections are in accordance with a central prediction of optimal feedback control theory and mirror the sophistication seen in feedback responses to mechanical and visual perturbations of the upper limb.NEW & NOTEWORTHY Correcting limb movements for external perturbations is a hallmark of flexible sensorimotor behavior. While visual and mechanical perturbations are corrected in a task-dependent manner, it is unclear whether a vestibular perturbation, naturally arising when the body moves, is selectively processed in reach control. We show, using galvanic vestibular stimulation, that reach corrections to vestibular perturbations are task dependent, consistent with a prediction of optimal feedback control theory.