Vestibular contribution to three-dimensional dynamic (allocentric) and two-dimensional static (egocentric) spatial memory

Vestibular contribution to spatial orientation and navigation

PURPOSE OF REVIEW

The vestibular system provides three-dimensional idiothetic cues for updating of one's position in space during head and body movement. Ascending vestibular signals reach entorhinal and hippocampal networks via head-direction pathways, where they converge with multisensory information to tune the place and grid cell code.

RECENT FINDINGS

Animal models have provided insight to neurobiological consequences of vestibular lesions for cerebral networks controlling spatial cognition. Multimodal cerebral imaging combined with behavioural testing of spatial orientation and navigation performance as well as strategy in the last years helped to decipher vestibular-cognitive interactions also in humans.

SUMMARY

This review will update the current knowledge on the anatomical and cellular basis of vestibular contributions to spatial orientation and navigation from a translational perspective (animal and human studies), delineate the behavioural and functional consequences of different vestibular pathologies on these cognitive domains, and will lastly speculate on a potential role of vestibular dysfunction for cognitive aging and impeding cognitive impairment in analogy to the well known effects of hearing loss.

The overarching effects of vestibular deficit: Imbalance, anxiety, and spatial disorientation

BACKGROUND

Comorbid Balance, Anxiety, and Spatial symptoms are observed in neurodevelopmental disorders and aging. Each of these symptoms was studied separately in association with vestibular hypofunction. We aimed to investigate whether such a diffuse range of symptoms has common vestibular pathophysiology. Specifically, we tested whether this Triad of dysfunctions is associated with central or peripheral vestibular hypofunction. We also assessed the possible contribution of semicircular canals (SCCs) vs. saccular function.

METHODS

We tested patients with Peripheral bilateral and unilateral Vestibular Hypofunction (PVH), Machado Joseph Disease (MJD) with cerebellar and central bilateral vestibular hypofunction, and healthy controls. SCCs and sacculi functioning were evaluated by the video Head Impulse Test (vHIT) and cervical Vestibular Evoked Myogenic Potentials (cVEMP), respectively. Balance was assessed by the Activities-specific Balance Confidence scale (ABC), anxiety by the Hamilton Anxiety Rating Scale (HAM-A), and spatial orientation by the Object Perspective Taking test (OPT-t).

RESULTS

PVH patients with vestibular SCCs and saccular hypofunction presented the Triad of symptoms, imbalance, anxiety, and spatial disorientation. MJD patients with SCCs-related vestibular hypofunction but preserved saccular-related vestibular function presented with a partial profile of imbalance and spatial disorientation.

CONCLUSIONS

The present study provides evidence that peripheral vestibular hypofunction is associated with the Triad of dysfunctions, i.e., imbalance, anxiety, and spatial disorientation. The combination of SCCs and saccular hypofunction seems to contribute to the emergence of the Triad of symptoms.

Reliability of the triangle completion test in the real-world and in virtual reality

Background

The triangle completion test has been used to assess egocentric wayfinding for decades, yet there is little information on its reliability. We developed a virtual reality (VR) based test and investigated whether either test of spatial navigation was reliable.

Objective

To examine test-retest reliability of the real-world and VR triangle completion tests. A secondary objective was to examine the usability of the VR based test.

Materials and methods

Thirty healthy adults aged 18–45 years were recruited to this block randomized study. Participants completed two sessions of triangle completion tests in the real-world and VR on the same day with a break between sessions.

Results

In both test versions distance from the endpoint and angle of deviation showed poor test-retest reliability (r < 0.5). Distance traveled had moderate reliability in both the real-world and VR tests (r = 0.55 95% CI [0.23, 0.76]; r = 0.66 95% CI [0.4, 0.83, respectively]). The VR triangle test showed poor correlation with the real-world test.

Conclusion

The triangle completion test has poor test-retest reliability and demonstrates poor concurrent validity between the real-world and VR. Nevertheless, it was feasible to translate a real-world test of spatial navigation into VR. VR provides opportunities for development of clinically relevant spatial navigation tests in the future.

Performance in Real World- and Virtual Reality-Based Spatial Navigation Tasks in Patients With Vestibular Dysfunction

OBJECTIVE

This study evaluated whether vestibular dysfunction is associated with reduced spatial navigation performance.

STUDY DESIGN

Cross-sectional study.

SETTING

Otolaryngology Clinic in the Johns Hopkins Outpatient Center and an analogous virtual reality (VR) environment.

PATIENTS

Eligible patients had diagnosis of unilateral or bilateral vestibular loss. Matched healthy controls were recruited at 1:1 ratio.

INTERVENTIONS

The navigation task involved a route-based or place-based strategy in both real world and VR environments.

MAIN OUTCOME MEASURES

Navigation performance was measured by distance travelled relative to optimal distance (i.e., path ratio) and the Judgments of Relative Direction (JRD) task, whereby participants had to recall relative angular distances between landmarks.

RESULTS

The study sample included 20 patients with vestibular loss (mean age: 61 yrs, SD: 10.2 yrs) and 20 matched controls (mean age: 60 yrs, SD: 10.4 yrs). Patients with vestibular loss travelled significantly greater distance using both route-based (path ratio 1.3 vs. 1.0, p = 0.02) and place-based (path ratio 2.6 vs. 2.0, p = 0.03) strategies in the real world. Overall, participants performed worse in virtual reality compared to real world in both path ratio (2.2 vs. 1.7; p = 0.04) and JRD error (78° vs. 67°; p < 0.01). Furthermore, while controls exhibited significant positive correlations between real world and VR performance in place-based (β = 0.75; p < 0.001) and JRD tasks (β = 0.70; p < 0.001), patients with vestibular loss exhibited no similar correlations.

CONCLUSIONS

The vestibular system appears to play a role in navigation ability during both actual and virtual navigation, suggesting a role for static vestibular signals in navigation performance.

Bilateral vestibulopathy causes selective deficits in recombining novel routes in real space

The differential impact of complete and incomplete bilateral vestibulopathy (BVP) on spatial orientation, visual exploration, and navigation-induced brain network activations is still under debate. In this study, 14 BVP patients (6 complete, 8 incomplete) and 14 age-matched healthy controls performed a navigation task requiring them to retrace familiar routes and recombine novel routes to find five items in real space. [¹⁸F]-fluorodeoxyglucose-PET was used to determine navigation-induced brain activations. Participants wore a gaze-controlled, head-fixed camera that recorded their visual exploration behaviour. Patients performed worse, when recombining novel routes (p < 0.001), whereas retracing of familiar routes was normal (p = 0.82). These deficits correlated with the severity of BVP. Patients exhibited higher gait fluctuations, spent less time at crossroads, and used a possible shortcut less often (p < 0.05). The right hippocampus and entorhinal cortex were less active and the bilateral parahippocampal place area more active during navigation in patients. Complete BVP showed reduced activations in the pontine brainstem, anterior thalamus, posterior insular, and retrosplenial cortex compared to incomplete BVP. The navigation-induced brain activation pattern in BVP is compatible with deficits in creating a mental representation of a novel environment. Residual vestibular function allows recruitment of brain areas involved in head direction signalling to support navigation.

Research on the Relationship Between Vestibular Migraine With/Without Cognitive Impairment and Brainstem Auditory Evoked Potential

Background: Vestibular migraine (VM) is the most common cause of spontaneous vertigo with no specific physical and laboratory examinations, and is an under-recognized entity with substantial burden for the individual and the society. In this study, by observing the brainstem auditory evoked potential (BAEP) and cognitive function of VM patients, the possible laboratory diagnostic indicators of VM and the influence of disease on cognitive function were discussed. Method: The study included 78 VM patients, 76 migraine patients, and 79 healthy individuals. The age, gender, and other clinical history of the three groups matched. All participants underwent BAEP examinations, in which patients in the migraine group and outpatients of the VM group were in the interictal period, and inpatients in the VM group were examined during episodes, while all patients tested for the Addenbrooke's cognitive examination-revised (ACE-R) scale were in the interictal period. The differences in BAEP and ACE-R scores between the three groups of members and their relationship with the clinical features of VM patients were analyzed. Result: The peak latency of I, III, and V wave in the BAEP of the VM group was longer than that of the migraine group and the control group (p < 0.05). The peak latency of V wave in the BAEP of the migraine group was longer than that of the control group (p < 0.05). The ACE-R of the VM group scored lower than the migraine group in terms of language fluency and language (p < 0.05), and lower than the control group in terms of total score, language fluency, language, and visuospatial (p < 0.05); and the ACE-R of the migraine group scored lower than the control group in the total score and visuospatial (p < 0.05). Conclusion: Migraine patients have brainstem dysfunction, and VM patients have more severe brainstem dysfunction than migraine patients, suggesting that VM patients have both central nervous system damage and peripheral nerve damage. Migraine patients have cognitive impairment, while cognitive impairment in VM patients is more severe than in migraine patients.

Testing Navigation in Real Space: Contributions to Understanding the Physiology and Pathology of Human Navigation Control

Successful navigation relies on the flexible and appropriate use of metric representations of space or topological knowledge of the environment. Spatial dimensions (2D vs. 3D), spatial scales (vista-scale vs. large-scale environments) and the abundance of visual landmarks critically affect navigation performance and behavior in healthy human subjects. Virtual reality (VR)-based navigation paradigms in stationary position have given insight into the major navigational strategies, namely egocentric (body-centered) and allocentric (world-centered), and the cerebral control of navigation. However, VR approaches are biased towards optic flow and visual landmark processing. This major limitation can be overcome to some extent by increasingly immersive and realistic VR set-ups (including large-screen projections, eye tracking and use of head-mounted camera systems). However, the highly immersive VR settings are difficult to apply particularly to older subjects and patients with neurological disorders because of cybersickness and difficulties with learning and conducting the tasks. Therefore, a need for the development of novel spatial tasks in real space exists, which allows a synchronous analysis of navigational behavior, strategy, visual explorations and navigation-induced brain activation patterns. This review summarizes recent findings from real space navigation studies in healthy subjects and patients with different cognitive and sensory neurological disorders. Advantages and limitations of real space navigation testing and different VR-based navigation paradigms are discussed in view of potential future applications in clinical neurology.

Perception of Verticality and Vestibular Disorders of Balance and Falls

Objective: To review current knowledge of the perception of verticality, its normal function and disorders. This is based on an integrative graviceptive input from the vertical semicircular canals and the otolith organs.

Methods: The special focus is on human psychophysics, neurophysiological and imaging data on the adjustments of subjective visual vertical (SVV) and the subjective postural vertical. Furthermore, examples of mathematical modeling of specific vestibular cell functions for orientation in space in rodents and in patients are briefly presented.

Results: Pathological tilts of the SVV in the roll plane are most sensitive and frequent clinical vestibular signs of unilateral lesions extending from the labyrinths via the brainstem and thalamus to the parieto-insular vestibular cortex. Due to crossings of ascending graviceptive fibers, peripheral vestibular and pontomedullary lesions cause ipsilateral tilts of the SVV; ponto-mesencephalic lesions cause contralateral tilts. In contrast, SVV tilts, which are measured in unilateral vestibular lesions at thalamic and cortical levels, have two different characteristic features: (i) they may be ipsi- or contralateral, and (ii) they are smaller than those found in lower brainstem or peripheral lesions. Motor signs such as head tilt and body lateropulsion, components of ocular tilt reaction, are typical for vestibular lesions of the peripheral vestibular organ and the pontomedullary brainstem (vestibular nucleus). They are less frequent in midbrain lesions (interstitial nucleus of Cajal) and rare in cortical lesions. Isolated body lateropulsion is chiefly found in caudal lateral medullary brainstem lesions. Vestibular function in the roll plane and its disorders can be mathematically modeled by an attractor model of angular head velocity cell and head direction cell function. Disorders manifesting with misperception of the body vertical are the pusher syndrome, the progressive supranuclear palsy, or the normal pressure hydrocephalus; they may affect roll and/or pitch plane.

Conclusion: Clinical determinations of the SVV are easy and reliable. They indicate acute unilateral vestibular dysfunctions, the causative lesion of which extends from labyrinth to cortex. They allow precise topographical diagnosis of side and level in unilateral brainstem or peripheral vestibular disorders. SVV tilts may coincide with or differ from the perception of body vertical, e.g., in isolated body lateropulsion.

3-D spatial memory and navigation: functions and disorders

PURPOSE OF REVIEW

The aim of this review is to report on the specialized neuronal systems mediating spatial orientation and navigation discovered in animal experiments. These findings have important implications for the clinical management of patients with vestibular disorders or dementia and for translational research in these fields.

RECENT FINDINGS

The following anatomically and functionally separate, but nevertheless cooperative cell types have been characterized: angular head velocity cells and head direction cells, which depend on vestibular input and interact with place cells and grid cells, which represent position and distance. The entire system is thought to encode internal cognitive maps whose spatial data can be utilized for navigation and orientation. Flying and swimming species use spatial orientation and navigation isotropically, i.e., in the earth-horizontal and vertical directions, whereas ground-based species, including humans, perform better in the earth-horizontal plane (anisotropically). Examples of clinical disorders with deficits of spatial orientation and navigation are bilateral peripheral vestibulopathy, mild cognitive impairment, and dementia.

SUMMARY

Testing spatial orientation and navigation should become an integral part of routine neurological examinations, especially in the elderly. Also desirable are the further development and standardization of simple and reliable smart phone-based bedside tests to measure these functions in patients.

The parietal lobe and the vestibular system

The vestibular cortex differs in various ways from other sensory cortices. It consists of a network of several distinct and separate temporoparietal areas. Its core region, the parietoinsular vestibular cortex (PIVC), is located in the posterior insula and retroinsular region and includes the parietal operculum. The entire network is multisensory (in particular, vestibular, visual, and somatosensory). The peripheral and central vestibular systems are bilaterally organized; there are various pontomesencephalic brainstem crossings and at least two transcallosal connections of both hemispheres, between the PIVC and the motion-sensitive visual cortex areas, which also mediate vestibular input. Structural and functional vestibular dominance characterizes the right hemisphere in right-handers and the left hemisphere in left-handers. This explains why right-hemispheric lesions in right-handers more often generally cause hemispatial neglect and the pusher syndrome, both of which involve vestibular function. Vestibular input also contributes to cognition and may determine individual lateralization of brain functions such as handedness. Bilateral organization is a major key to understanding cortical functions and disorders, for example, the visual-vestibular interaction that occurs in spatial orientation. Although the vestibular cortex is represented in both hemispheres, there is only one global percept of body position and motion. The chiefly vestibular aspects of the multiple functions and disorders of the parietal lobe dealt with in this chapter cannot be strictly separated from various multisensory vestibular functions within the entire brain.