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

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.

Functional Dizziness as a Spatial Cognitive Dysfunction

(1) Background: Persistent postural-perceptual dizziness (PPPD) is a common chronic dizziness disorder with an unclear pathophysiology. It is hypothesized that PPPD may involve disrupted spatial cognition processes as a core feature. (2) Methods: A cohort of 19 PPPD patients underwent psycho-cognitive testing, including assessments for anxiety, depression, memory, attention, planning, and executive functions, with an emphasis on spatial navigation via a virtual Morris water maze. These patients were compared with 12 healthy controls and 20 individuals with other vestibular disorders but without PPPD. Vestibular function was evaluated using video head impulse testing and vestibular evoked myogenic potentials, while brain magnetic resonance imaging was used to exclude confounding pathology. (3) Results: PPPD patients demonstrated unique impairments in allocentric spatial navigation (as evidenced by the virtual Morris water maze) and in other high-demand visuospatial cognitive tasks that involve executive functions and planning, such as the Towers of London and Trail Making B tests. A factor analysis highlighted spatial navigation and advanced visuospatial functions as being central to PPPD, with a strong correlation to symptom severity. (4) Conclusions: PPPD may broadly impair higher cognitive functions, especially in spatial cognition. We discuss a disruption in the creation of enriched cognitive spatial maps as a possible pathophysiology for PPPD.

[Clinical examination of spatial neglect and other disorders of spatial cognition]

Neglect occurring after stroke, neoplasms or degenerative processes can lead to considerable disability in everyday life as can other disorders of spatial orientation. Therefore, a dedicated examination and early diagnostic classification are obligatory. Behavioral tests are helpful in this respect, enabling the clinician to obtain an initial overview of the existing deficits even at the patient's bedside. The clinical (bedside) examination of spatial neglect as well as the corresponding differential diagnostic procedure for the clarification of (possibly additionally or exclusively existing) hemianopia and extinction, as well as the examination of disorders of visuospatial perception, visuoconstructive disorders, topographic disorders, Bálint's syndrome, simultanagnosia, and optic ataxia are presented. The presentation is based on the newly revised (year 2023) guidelines of the Association of the Scientific Medical Societies in Germany (AWMF) on this subject area.

Different approaches to test orientation of self in space: comparison of a 2D pen-and-paper test and a 3D real-world pointing task

Spatial orientation is based on a complex cortical network with input from multiple sensory systems. It is affected by training, sex and age as well as cultural and psychological factors, resulting in different individual skill levels in healthy subjects. Various neurological disorders can lead to different patterns or specific deficits of spatial orientation and navigation. Accordingly, numerous tests have been proposed to assess these abilities. Here, we compare the results of (1) a validated questionnaire-based self-estimate of orientation/navigation ability (Santa Barbara Sense of Direction Scale, SBSODS) and (2) a validated pen-and-paper two-dimensional perspective test (Perspective Taking Spatial Orientation Test, SOT) with (3) a newly developed test of finger-arm pointing performance in a 3D real-world (3D-RWPT) paradigm using a recently established pointing device. A heterogeneous group of 121 participants (mean age 56.5 ± 17.7 years, 52 females), including 16 healthy volunteers and 105 patients with different vestibular, ocular motor and degenerative brain disorders, was included in this study. A high correlation was found between 2D perspective task and 3D pointing along the horizontal (azimuth) but not along the vertical (polar) plane. Self-estimated navigation ability (SBSODS) could not reliably predict actual performance in either 2D- or 3D-tests. Clinical assessment of spatial orientation and memory should therefore include measurements of actual performance, based on a 2D pen-and-paper test or a 3D pointing task, rather than memory-based questionnaires, since solely relying on the patient's history of self-estimated navigation ability results in misjudgments. The 3D finger-arm pointing test (3D-RWPT) reveals additional information on vertical (polar) spatial performance which goes undetected in conventional 2D pen-and-paper tests. Diseases or age-specific changes of spatial orientation in the vertical plane should not be clinically neglected. The major aim of this pilot study was to compare the practicability and capability of the three tests but not yet to prove their use for differential diagnosis. The next step will be to establish a suitable clinical bedside test for spatial memory and orientation.

Different strategies in pointing tasks and their impact on clinical bedside tests of spatial orientation

Deficits in spatial memory, orientation, and navigation are often early or neglected signs of degenerative and vestibular neurological disorders. A simple and reliable bedside test of these functions would be extremely relevant for diagnostic routine. Pointing at targets in the 3D environment is a basic well-trained common sensorimotor ability that provides a suitable measure. We here describe a smartphone-based pointing device using the built-in inertial sensors for analysis of pointing performance in azimuth and polar spatial coordinates. Interpretation of the vectors measured in this way is not trivial, since the individuals tested may use at least two different strategies: first, they may perform the task in an egocentric eye-based reference system by aligning the fingertip with the target retinotopically or second, by aligning the stretched arm and the index finger with the visual line of sight in allocentric world-based coordinates similar to using a rifle. The two strategies result in considerable differences of target coordinates. A pilot test with a further developed design of the device and an app for a standardized bedside utilization in five healthy volunteers revealed an overall mean deviation of less than 5° between the measured and the true coordinates. Future investigations of neurological patients comparing their performance before and after changes in body position (chair rotation) may allow differentiation of distinct orientational deficits in peripheral (vestibulopathy) or central (hippocampal or cortical) disorders.

The Role of the Precuneus in Human Spatial Updating in a Real Environment Setting-A cTBS Study

As we move through an environment, we update positions of our body relative to other objects, even when some objects temporarily or permanently leave our field of view—this ability is termed egocentric spatial updating and plays an important role in everyday life. Still, our knowledge about its representation in the brain is still scarce, with previous studies using virtual movements in virtual environments or patients with brain lesions suggesting that the precuneus might play an important role. However, whether this assumption is also true when healthy humans move in real environments where full body-based cues are available in addition to the visual cues typically used in many VR studies is unclear. Therefore, in this study we investigated the role of the precuneus in egocentric spatial updating in a real environment setting in 20 healthy young participants who underwent two conditions in a cross-over design: (a) stimulation, achieved through applying continuous theta-burst stimulation (cTBS) to inhibit the precuneus and (b) sham condition (activated coil turned upside down). In both conditions, participants had to walk back with blindfolded eyes to objects they had previously memorized while walking with open eyes. Simplified trials (without spatial updating) were used as control condition, to make sure the participants were not affected by factors such as walking blindfolded, vestibular or working memory deficits. A significant interaction was found, with participants performing better in the sham condition compared to real stimulation, showing smaller errors both in distance and angle. The results of our study reveal evidence of an important role of the precuneus in a real-environment egocentric spatial updating; studies on larger samples are necessary to confirm and further investigate this finding.

[Autonomous Neurology within the University Hospital of LMU at 50 years]

Establishment of the Chair of Neurology at the University of Munich in 1971 as well as the opening of the Neurology Department at the newly built Großhadern campus (1974) provide an occasion to review the 50 years that have passed since. Further, the early history of Munich neurology is described, with its slow pace of separation (in comparison to e.g. Heidelberg, Frankfurt and Hamburg) from the parent disciplines, psychiatry and internal medicine. In Munich, they were long shaped by psychiatrists such as Bernhard von Gudden, Emil Kraepelin, Kurt Kolle and Hanns Hippius and by Friedrich von Müller and, in particular, by Gustav Bodechtel in internal medicine.Once independent, further development of neurology in Munich was characterized by fast-paced, almost revolutionary changes in neuroimaging, electrophysiology, sonography, and engineering as well as in basic neuroscience, neurogenetics included. The new department thrived under the leadership of Adolf Schrader (from 1971), Thomas Brandt (from 1984) and Marianne Dieterich (from 2008) who enjoyed the support of an ever-increasing specialised clinical-scientific staff.Evidence-based treatment of neurological disorders became the overarching and internationally visible focus of Munich neurology, with respect to both practical implementation and to research. The exemplary diseases and syndromes of multiple sclerosis, epilepsy, stroke, movement disorders, dizziness and disorders of balance and gait as well as diseases of the musculature and peripheral nerves are cared for not only within the inpatient and outpatient sections of the Neurology Department but also by units such as the Friedrich Baur Institute (FBI), the German Dizziness and Balance Centre (DSGZ), the Institutes for Stroke and Dementia Research (ISD) and for Clinical Neuroimmunology as well as in the interdisciplinary Department of Palliative Care.

Navigation strategies in patients with vestibular loss tested in a virtual reality T-maze

During navigation, humans mainly rely on egocentric and allocentric spatial strategies, two different frames of reference working together to build a coherent representation of the environment. Spatial memory deficits during navigation have been repeatedly reported in patients with vestibular disorders. However, little is known about how vestibular disorders can change the use of spatial navigation strategies. Here, we used a new reverse T-maze paradigm in virtual reality to explore whether vestibular loss specifically modifies the use of egocentric or allocentric spatial strategies in patients with unilateral (n = 23) and bilateral (n = 23) vestibular loss compared to healthy volunteers (n = 23) matched for age, sex and education level. Results showed that the odds of selecting and using a specific strategy in the T-maze were significantly reduced in both unilateral and bilateral vestibular loss. An exploratory analysis suggests that only right vestibular loss decreased the odds of adopting a spatial strategy, indicating an asymmetry of vestibular functions. When considering patients who used strategies to navigate, we observed that a bilateral vestibular loss reduced the odds to use an allocentric strategy, whereas a unilateral vestibular loss decreased the odds to use an egocentric strategy. Age was significantly associated with an overall lower chance to adopt a navigation strategy and, more specifically, with a decrease in the odds of using an allocentric strategy. We did not observe any sex difference in the ability to select and use a specific navigation strategy. Findings are discussed in light of previous studies on visuo-spatial abilities and studies of vestibulo-hippocampal interactions in peripheral vestibular disorders. We discuss the potential impact of the history of the disease (chronic stage in patients with a bilateral vestibulopathy vs. subacute stage in patients with a unilateral vestibular loss), of hearing impairment and non-specific attentional deficits in patients with vestibular disorders.

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.

Have I Been Here? Sense of Location in People With Alzheimer's Disease

Background: When navigating in a particular space, a sense of being at a current location is of great help for the navigators in reaching their destination or getting back to the start. To accomplish this work, interwoven neural structures and neurons are called into play. This system is called the heading direction cell-place cell-grid cell circuit. Evidence from various neuroscience studies has revealed that the regions responsible for this circuit are damaged in the early stages of Alzheimer's disease (AD). This may explain why wayfinding difficulty is one of the most frequent symptoms in persons with AD. The aim of this study was to examine the sense of location (SoL) in persons with mild AD, persons with prodromal AD (prAD), and those who were cognitively unimpaired (CU). Methods: We invited people with mild AD, prAD, and CU to participate in this study. The venue of the core experiment to assess SoL was a 660-m path located on the university campus. The participants were instructed to take a walk on the path and press a device to indicate their arrival at each of the five carefully chosen targets. The linear deviations from the target site were compared among the groups. Results: A total of 20 AD, 28 prAD, and 29 CU persons completed the study. Their Mini-Mental State Examination scores were on average 20 (SD 3), 24 (SD 3), and 28 (SD 2). The groups were well differentiated regarding several measurements for cognitive ability and spatial navigation. As for the SoL, the hit rates of exact location with linear deviation of 16 m or less were 0.05, 0.54, and 0.86 for AD, prAD, and CU persons, respectively. The hit rates were well correlated with the presence of getting lost. Also, SoL differentiated well among CU, PrAD, and AD in terms of average linear deviation. Conclusions: Our employing linear deviation by utilizing a grid-cell function device as an assessment for SoL showed distinct features among the three groups. This model can be used to develop more delicate devices or instruments to detect, monitor, and aid spatial navigation in persons with prAD and AD.

Spontaneous visual exploration during locomotion in patients with phobic postural vertigo

Background

Earlier studies on stance and gait with posturographic and EMG-recordings and automatic gait analysis in patients with phobic postural vertigo (PPV) or visual height intolerance (vHI) revealed similar patterns of body stiffening with muscle co-contraction and a slow, cautious gait. Visual exploration in vHI patients was characterized by a freezing of gaze-in-space when standing and reduced horizontal eye and head movements during locomotion.

Objective

Based on the findings in vHI patients, the current study was performed with a focus on visual control of locomotion in patients with PPV while walking along a crowded hospital hallway.

Methods

Twelve patients with PPV and eleven controls were recruited. Participants wore a mobile infrared video eye-tracking system that continuously measured eye-in-head movements in the horizontal and vertical planes and head orientation and motion in the yaw, pitch, and roll planes. Visual exploration behavior of participants was recorded at the individually preferred speed for a total walking distance of 200 m. Gaze-in-space directions were determined by combining eye-in-head and head-in-space orientation. Walking speeds were calculated based on the trial duration and the total distance traversed. Participants were asked to rate their feelings of discomfort during the walk on a 4-point numeric rating scale. The examiners rated the crowdedness of the hospital hallway on a 4-point numeric rating scale.

Results

The major results of visual exploration behavior in patients with PPV in comparison to healthy controls were: eye and head positions were directed more downward in the vertical plane towards the ground ahead with increased frequency of large amplitude vertical orientation movements towards the destination, the end of the ground straight ahead. The self-adjusted speed of locomotion was significantly lower in PPV. Particularly those patients that reported high levels of discomfort exhibited a specific visual exploration of their horizontal surroundings. The durations of fixating targets in the visual surroundings were significantly shorter as compared to controls.

Conclusion

Gaze control of locomotion in patients with PPV is characterized by a preferred deviation of gaze more downward and by horizontal explorations for suitable auxiliary means for potential postural support in order to prevent impending falls. These eye movements have shorter durations of fixation as compared to healthy controls and patients with vHI. Finally, the pathological alterations in eye–head coordination during locomotion correlate with a higher level of discomfort and anxiety about falling.

Reframing spatial frames of reference: What can aging tell us about egocentric and allocentric navigation?

Representations of space in mind are crucial for navigation, facilitating processes such as remembering landmark locations, understanding spatial relationships between objects, and integrating routes. A significant problem, however, is the lack of consensus on how these representations are encoded and stored in memory. Specifically, the nature of egocentric and allocentric frames of reference in human memory is widely debated. Yet, in recent investigations of the spatial domain across the lifespan, these distinctions in mnemonic spatial frames of reference have identified age-related impairments. In this review, we survey the ways in which different terms related to spatial representations in memory have been operationalized in past aging research and suggest a taxonomy to provide a common language for future investigations and theoretical discussion. This article is categorized under: Psychology > Memory Neuroscience > Cognition Psychology > Development and Aging.

Postural Control While Walking Interferes With Spatial Learning in Older Adults Navigating in a Real Environment

Cognitive demands for postural control increase with aging and cognitive-motor interference (CMI) exists for a number of walking situations, especially with visuo-spatial cognitive tasks. Such interference also influences spatial learning abilities among older adults; however, this is rarely considered in research on aging in spatial navigation. We posited that visually and physically exploring an unknown environment may be subject to CMI for older adults. We investigated potential indicators of postural control interfering with spatial learning. Given known associations between age-related alterations in gait and brain structure, we also examined potential neuroanatomical correlates of this interference. Fourteen young and 14 older adults had to find an invisible goal in an unfamiliar, real, ecological environment. We measured walking speed, trajectory efficiency (direct route over taken route) and goal fixations (proportion of visual fixations toward the goal area). We calculated the change in walking speed between the first and last trials and adaptation indices for all three variables to quantify their modulation across learning trials. All participants were screened with a battery of visuo-cognitive tests. Eighteen of our participants (10 young, 8 older) also underwent a magnetic resonance imaging (MRI) examination. Older adults reduced their walking speed considerably on the first, compared to the last trial. The adaptation index of walking speed correlated positively with those of trajectory efficiency and goal fixations, indicating a reduction in resource sharing between walking and encoding the environment. The change in walking speed correlated negatively with gray matter volume in superior parietal and occipital regions and the precuneus. We interpret older adults’ change in walking speed as indicative of CMI, similar to dual task costs. This is supported by the correlations between the adaptation indices and between the change in walking speed and gray matter volume in brain regions that are important for navigation, given that they are involved in visual attention, sensory integration and encoding of space. These findings under ecological conditions in a natural spatial learning task question what constitutes dual tasking in older adults and they can lead future research to reconsider the actual cognitive burden of postural control in aging navigation research.