Path Integration Task Research Articles

Real-space path integration is impaired in Alzheimer’s disease and mild cognitive impairment

IntroductionPath integration (PI) is an important component of spatial navigation that integrates self-motion cues to allow the subject to return to a starting point. PI depends on the structures affected early in the course of Alzheimer’s disease (AD) such as the medial temporal lobe and the parietal cortex. ObjectivesTo assess whether PI is impaired in patients with mild AD and amnestic mild cognitive impairment (aMCI) and to investigate the role of the hippocampus, entorhinal and inferior parietal cortex in this association. Methods27 patients with aMCI, 14 with mild AD and 18 controls completed eight trials of Arena Path Integration Task. The task required subjects with a mask covering their eyes to follow an enclosed triangle pathway through two previously seen places: start–place1–place2–start. Brains were scanned at 1.5T MRI and respective volumes and thicknesses were derived using FreeSurfer algorithm. ResultsControlling for age, education, gender and Mini-Mental State Examination score the aMCI and AD subjects were impaired in PI accuracy on the pathway endpoint (p=0.042 and p=0.013) compared to controls. Hippocampal volume and thickness of entorhinal and parietal cortices explained separately 36–45% of the differences in PI accuracy between controls and aMCI and 28–31% of the differences between controls and AD subjects. ConclusionsPI is affected in aMCI and AD, possibly as a function of neurodegeneration in the medial temporal lobe structures and the parietal cortex. PI assessment (as a part of spatial navigation testing) may be useful for identification of patients with incipient AD.

EEG correlates of spatial orientation in the human retrosplenial complex

Studies on spatial navigation reliably demonstrate that the retrosplenial complex (RSC) plays a pivotal role for allocentric spatial information processing by transforming egocentric and allocentric spatial information into the respective other spatial reference frame (SRF). While more and more imaging studies investigate the role of the RSC in spatial tasks, high temporal resolution measures such as electroencephalography (EEG) are missing. To investigate the function of the RSC in spatial navigation with high temporal resolution we used EEG to analyze spectral perturbations during navigation based on allocentric and egocentric SRF. Participants performed a path integration task in a clearly structured virtual environment providing allothetic information. Continuous EEG recordings were decomposed by independent component analysis (ICA) with subsequent source reconstruction of independent time source series using equivalent dipole modeling. Time–frequency transformation was used to investigate reference frame-specific orientation processes during navigation as compared to a control condition with identical visual input but no orientation task. Our results demonstrate that navigation based on an egocentric reference frame recruited a network including the parietal, motor, and occipital cortices with dominant perturbations in the alpha band and theta modulation in frontal cortex. Allocentric navigation was accompanied by performance-related desynchronization of the 8–13Hz frequency band and synchronization in the 12–14Hz band in the RSC. The results support the claim that the retrosplenial complex is central to translating egocentric spatial information into allocentric reference frames. Modulations in different frequencies with different time courses in the RSC further provide first evidence of two distinct neural processes reflecting translation of spatial information based on distinct reference frames and the computation of heading changes.

The retrosplenial cortex is necessary for path integration in the dark

An increasing amount of data indicates that the retrosplenial cortex (RSC) plays a role in navigation and spatial memory. Moreover, it has been suggested that the RSC integrates mnemonic spatial features of the environment with self-motion information therefore enabling accurate path integration in darkness. This hypothesis rests on data obtained from animals trained in spatial memory tasks involving the conjoint use of allothetic and idiothetic information [8]. We examined the contribution of the RSC when animals are submitted to a path integration task with minimal memory requirement in light and dark. We found that RSC-lesioned rats exhibited a path integration deficit in the dark but not in the light. This suggests that the RSC is important for path integration and incorporates visuospatial information to maintain path integration accuracy.

Real world navigation independence in the early blind correlates with differential brain activity associated with virtual navigation

Navigating is a complex cognitive task that places high demands on spatial abilities, particularly in the absence of sight. Significant advances have been made in identifying the neural correlates associated with various aspects of this skill; however, how the brain is able to navigate in the absence of visual experience remains poorly understood. Furthermore, how neural network activity relates to the wide variability in navigational independence and skill in the blind population is also unknown. Using functional magnetic resonance imaging, we investigated the neural correlates of audio-based navigation within a large scale, indoor virtual environment in early profoundly blind participants with differing levels of spatial navigation independence (assessed by the Santa Barbara Sense of Direction scale). Performing path integration tasks in the virtual environment was associated with activation within areas of a core network implicated in navigation. Furthermore, we found a positive relationship between Santa Barbara Sense of Direction scores and activation within right temporal parietal junction during the planning and execution phases of the task. These findings suggest that differential navigational ability in the blind may be related to the utilization of different brain network structures. Further characterization of the factors that influence network activity may have important implications regarding how this skill is taught in the blind community.

Reduced Vision Selectively Impairs Spatial Updating in Fall-prone Older Adults

The current study examined the role of vision in spatial updating and its potential contribution to an increased risk of falls in older adults. Spatial updating was assessed using a path integration task in fall-prone and healthy older adults. Specifically, participants conducted a triangle completion task in which they were guided along two sides of a triangular route and were then required to return, unguided, to the starting point. During the task, participants could either clearly view their surroundings (full vision) or visuo-spatial information was reduced by means of translucent goggles (reduced vision). Path integration performance was measured by calculating the distance and angular deviation from the participant's return point relative to the starting point. Gait parameters for the unguided walk were also recorded. We found equivalent performance across groups on all measures in the full vision condition. In contrast, in the reduced vision condition, where participants had to rely on interoceptive cues to spatially update their position, fall-prone older adults made significantly larger distance errors relative to healthy older adults. However, there were no other performance differences between fall-prone and healthy older adults. These findings suggest that fall-prone older adults, compared to healthy older adults, have greater difficulty in reweighting other sensory cues for spatial updating when visual information is unreliable.

Distinct Roles of Medial and Lateral Entorhinal Cortex in Spatial Cognition

It is known that the entorhinal cortex plays a crucial role in spatial cognition in rodents. Neuroanatomical and electrophysiological data suggest that there is a functional distinction between 2 subregions within the entorhinal cortex, the medial entorhinal cortex (MEC), and the lateral entorhinal cortex (LEC). Rats with MEC or LEC lesions were trained in 2 navigation tasks requiring allothetic (water maze task) or idiothetic (path integration) information processing and 2-object exploration tasks allowing testing of spatial and nonspatial processing of intramaze objects. MEC lesions mildly affected place navigation in the water maze and produced a path integration deficit. They also altered the processing of spatial information in both exploration tasks while sparing the processing of nonspatial information. LEC lesions did not affect navigation abilities in both the water maze and the path integration tasks. They altered spatial and nonspatial processing in the object exploration task but not in the one-trial recognition task. Overall, these results indicate that the MEC is important for spatial processing and path integration. The LEC has some influence on both spatial and nonspatial processes, suggesting that the 2 kinds of information interact at the level of the EC.

Linear Path Integration Deficits in Patients with Abnormal Vestibular Afference

Effective navigation requires the ability to keep track of one's location and maintain orientation during linear and angular displacements. Path integration is the process of updating the representation of body position by integrating internally-generated self-motion signals over time (e.g., walking in the dark). One major source of input to path integration is vestibular afference. We tested patients with reduced vestibular function (unilateral vestibular hypofunction, UVH), patients with aberrant vestibular function (benign paroxysmal positional vertigo, BPPV), and healthy participants (controls) on two linear path integration tasks: experimenter-guided walking and target-directed walking. The experimenter-guided walking task revealed a systematic underestimation of self-motion signals in UVH patients compared to the other groups. However, we did not find any difference in the distance walked between the UVH group and the control group for the target-directed walking task. Results from neuropsychological testing and clinical balance measures suggest that the errors in experimenter-guided walking were not attributable to cognitive and/or balance impairments. We conclude that impairment in linear path integration in UVH patients stem from deficits in self-motion perception. Importantly, our results also suggest that patients with a UVH deficit do not lose their ability to walk accurately without vision to a memorized target location.

Visual influence on path integration in darkness indicates a multimodal representation of large-scale space

Our ability to return to the start of a route recently performed in darkness is thought to reflect path integration of motion-related information. Here we provide evidence that motion-related interoceptive representations (proprioceptive, vestibular, and motor efference copy) combine with visual representations to form a single multimodal representation guiding navigation. We used immersive virtual reality to decouple visual input from motion-related interoception by manipulating the rotation or translation gain of the visual projection. First, participants walked an outbound path with both visual and interoceptive input, and returned to the start in darkness, demonstrating the influences of both visual and interoceptive information in a virtual reality environment. Next, participants adapted to visual rotation gains in the virtual environment, and then performed the path integration task entirely in darkness. Our findings were accurately predicted by a quantitative model in which visual and interoceptive inputs combine into a single multimodal representation guiding navigation, and are incompatible with a model of separate visual and interoceptive influences on action (in which path integration in darkness must rely solely on interoceptive representations). Overall, our findings suggest that a combined multimodal representation guides large-scale navigation, consistent with a role for visual imagery or a cognitive map.

Walking speed and vestibular disorders in a path integration task

The goal of this study was to determine if parameters of gait are related to the path integration deficits in some people with vestibular disorders. We tested normals, and two groups of vestibularly impaired people, with unilateral benign paroxysmal positional vertigo and with unilateral weakness. Each group had 20 subjects. They walked straight ahead for 7.62m, with eyes open or closed, to the beat of a metronome at 60 beats/min, 120 beats/min and 176 beats/min. When adjusted for age and sex, normals veered significantly less and walked significantly further before veering than the unilateral weakness group; all groups veered significantly less at 120 beats/min than the slower or faster cadences. Older patients walked slightly but significantly slower than younger patients at the faster speeds. Step length did not differ among diagnostic groups. These data confirm the involvement of vestibular function in path integration, suggest a differentiation by type of vestibular impairment, and suggest some differences by cadence.

Bigger is better: Large visual displays improve spatial knowledge of a virtual environment

This study examined the effect of physical display size on spatial knowledge of a virtual environment (VE). Previous research by Tan (2004) found that performance for a path integration task in a VE was superior on a large display compared to a small one, even with visual angle held constant. This may be because large displays evoke a more egocentric frame of reference than small displays. To test whether the advantages of large displays extended to a navigation transfer task, the present studies examined the effect of display size on transferring knowledge about the spatial layout of a desktop VE to virtual reality (VR). Participants used a joystick to control their movement through a virtual city environment, finding and learning the locations of five targets separated by buildings. After 20 minutes of learning, participants’ spatial knowledge was tested in a fully immersive environment by using virtual reality. Participants stood at each target location and pointed to each of the other, unseen targets. In the first study participants learned the VE on either an 18” LCD display or a 112” projected display. Visual angle was not equated. In the second study participants learned the VE on either a 25” or 72” projected display and visual angle was held constant. In both studies we found the average angular pointing error was significantly lower on the large display. Our results suggest that the advantage of a large desktop display for a virtual environment transfers to VR and is not dependent on visual angle. Bigger is Better: Large Visual Displays Improve Spatial Knowledge of a Virtual Environment

Perceptual Encoding of Self‐Motion Duration in Human Posterior Parietal Cortex

It has been demonstrated previously that repetitive transcranial magnetic stimulation (rTMS) to right or left posterior parietal cortex (PPC) disrupts perceptual encoding of whole-body displacement during an angular path integration task using only vestibular cues for its completion. The effects of rTMS applied to right PPC (and left motor cortex as a control) during a vestibular-cued motion-reproduction task (i.e., not requiring path integration) were investigated in 5 subjects. Specifically, subjects were rotated in the dark on a motorized Bárány chair with raised cosine velocities of durations 1, 2, and 3 s and peak 30 degrees, 60 degrees, 90 degrees, and 120 degrees/s. Subjects were required to actively reproduce the motion profile after every rotation with a chair-bound joystick. It was found that rTMS applied to the right PPC during the passive (encoding) stimulus phase had no effect on angular velocity reproduction when compared to control (motor-cortex rTMS). In contrast, motion-duration reproduction was significantly worse with right PPC (versus control motor cortex) rTMS. The results imply that vestibular-derived cues of motion duration, but not velocity, are encoded in human PPC. It was inferred from these and previous data that human PPC is involved in human path integration and motion-duration perception, but not angular velocity self-motion perception.

The Effect of Dual Tasks in Locomotor Path Integration

Without landmarks, navigation is based on information about self-velocity, which is transformed to position or orientation by a process called path integration. Simple path integration tasks, such as reaching a previously seen goal by blindfolded locomotion, were often considered to be automatic and not influenced by unrelated cognitive activity. However, we recently showed that reproduction of self-motion without landmark cues exhibits systematic dual-task interference. Since these experiments did not exclude that the dual task only interferes with memory for self-motion, we performed two additional experiments testing generic path integration. We show that locomotor homing and reaching predefined goals by active self-motion are affected systematically by a concurrent mental task. The similarity of the effects we found to those reported for duration estimation led us to the hypothesis that subjective time may be used as a temporal basis of path integration. Alternatively, path integration and duration estimation may be based on similar underlying neuronal mechanisms, for example, coincidence detection in neural oscillators.

Comparison of Locomotion Interfaces for Immersive Training Systems

The ability to stay oriented in an environment is an important skill for urban combat. Warriors must systematically clear areas of responsibility while moving tactically, scanning for potential targets, and engaging threats. A locomotion interface for an immersive virtual environment urban combat training system should enable the development of navigational skills. One aspect of navigation is path integration, in which a person estimates current position and orientation along a pathway from velocity and acceleration. Path integration allows people to stay oriented in low visibility or the dark, which is important in many tactical situations. This study compared the performance of three locomotion interfaces on three path integration tasks. Analysis revealed that type of locomotion interface has a significant impact on performance.

Light compass in the provisioning navigation of the subsocial shield bug, Parastrachia japonensis (Heteroptera: Parastrachiidae)

The female of the subsocial shield bug, Parastrachia japonensis, provisions food to her nymphs using path integration, a type of navigational strategy that acquires information indicating the traveler's direction and distance. In this study we investigated whether and how P. japonensis females use a light compass involved in orientation at a constant angle with respect to a light source. First, we let the female run toward its burrow in an experimental room when a lamp set on the floor was turned on. Then, we changed the direction of the light source 180° horizontally by switching off the lamp and turning on another lamp on the opposite side. In response to this change, the homing bug turned back immediately. Next, we examined the effects of the light source from two different elevations. It accomplished its path integration task when the light was placed at an azimuth of 45°. When the light was at the zenith (90°), however, the bug lost the correct home direction. These results suggest that in their path integration system P. japonensis use light sources as compass references and, further, that they can estimate their direction from a point located at mid-sky but not the zenith.

Acquiring Spatial Knowledge While Traveling Simple and Complex Paths with Immersive and Nonimmersive Interfaces

Exploration of virtual environments may be accomplished with different interface metaphors. Previous research suggests that vestibular and proprioceptive information provided by immersive interfaces facilitates spatial orientation on simple path-integration tasks. We examine whether these interface variables impact performance across paths of variable complexity. Our immersive interface provided all users the ability to conduct the search component of our task more efficiently. Our results, however, show that the immersive interface was no more effective than our nonimmersive one for maintaining orientation. In fact, the immersive interface had a negative impact on performance (absolute error) for individuals who had extensive experience with playing video games. When measured in terms of consistency of response, our results suggest that having extensive game-play experience will negatively impact orientation performance with both interfaces. We speculate that this is due to the conflicting nature of the skills that avid game players acquire in game-play versus those required to perform in our task.

The acquisition of vector knowledge and its relation to self-rated direction sense.

Self-rated sense of direction is reliably related to people's accuracy when pointing in the direction of unseen landmarks from imagined or actual perspectives. It is proposed that the cognitive substrate of accurate pointing responses is a vector representation, which is defined as an integrated network of displacement vectors. Experiment 1 isolated the body senses and tested displacement vector formation in a path-integration task. Experiment 2 isolated the visual modality and tested displacement vector formation in a virtual-learning task. Both experiments tested whether people reporting a good sense of direction (GSOD) were more likely to compute displacement vectors than people reporting a poor sense of direction (PSOD). The results showed that both GSOD and PSOD people computed displacement vectors in the path-integration task, but not in the virtual-learning task. When interlandmark relations were visually specified, GSOD people made more accurate pointing responses than PSOD people, adding to a growing body of cognitive correlates of self-rated direction sense.

Improvements in path integration after vestibular rehabilitation

Fifty-three subjects with peripheral, chronic vestibulopathies, who were referred for vestibular rehabilitation, were tested on a path integration task before and after doing four weeks of five times daily habituation exercises for vertigo reduction. The task involved walking over a 7.62 m path with eyes closed. Dependent measures were velocity and angle of veering from the straight ahead. At the post-test and at succeeding follow-up tests for up to six months, subjects had significant increases in velocity and significant declines in angle of veering. Length of time subjects had vertigo prior to starting rehabilitation, and speed of head movement exercises were not associated with improvements. These data support the previous finding that patients with vestibular impairments have decreased performance on this task. The data also suggest that vestibular rehabilitation, given as a simple home program, is associated with improvements in this skill.

Rats can track odors, other rats, and themselves: implications for the study of spatial behavior

In order to demonstrate that rats solve dead reckoning (path integration) tasks in which they return to a starting location using self-movement (idiothetic) cues, it is necessary to remove external (allothetic) cues. Odor cues, especially those generated by a rat on a single passage, are difficult to control and they can potentially serve as a cue to guide a homeward trip. Because it is presently unknown whether rats can track the cues that they themselves leave, as opposed to the odor trails left by other rats, we investigated this question in the present study. A tracking task was used in which rats: (1) followed a scented string from a refuge to obtain a food pellet located on a large circular table; (2) followed odors left on the table; (3) followed odors left by the passage of another rat; or (4) followed odors left by themselves. Groups of rats were presented with strings scented with either the rat's own odor (Group Own), a conspecific's odor (Group Other), or another scent, vanilla (Group Vanilla). After training, a series of discrimination tests were given to determine the nature of the stimulus that controls scent tracking. The results indicated that Own, Other, and Vanilla groups were equally proficient in discriminating and following their respective odors. The rats were also able to follow odor trails on the table surface as well as a trail left by the single passage of another rat or their own passage. This is the first study to demonstrate that rats can discriminate between conspecific odors and their own odor left during a single passage. The results are discussed in relation to their implications for experimental methodology and olfactory contributions to spatial navigation in general and dead reckoning in particular.

Rat spatial memory tasks adapted for humans: characterization in subjects with intact brain and subjects with selective medial temporal lobe thermal lesions.

In the present paper we describe five tests, 3 of which were designed to be similar to tasks used with rodents. Results obtained from control subjects, patients with selective thermo-coagulation lesions to the medial temporal lobe and results from non-human primates and rodents are discussed. The tests involve memory for spatial locations acquired by moving around in a room, memory for objects subjects interacted with, or memory for objects and their locations. Two of the spatial memory tasks were designed specifically as analogs of the Morris water task and the 8-arm radial-maze tasks used with rats. The Morris water task was modeled by hiding a sensor under the carpet of a room (Invisible Sensor Task). Subjects had to learn its location by using an array of visual cues available in the room. A path integration task was developed in order to study the non-visual acquisition of a cognitive representation of the spatial location of objects. In the non-visual spatial memory task, we blindfolded subjects and led them to a room where they had to find 3 objects and remember their locations. We designed an object location task by placing 4 objects in a room that subjects observed for later recall of their locations. A recognition task, and a novelty detection task were given subsequent to the recall task. An 8-arm radial-maze was recreated by placing stands at equal distance from each other around the room, and asking subjects to visit each stand once, from a central point. A non-spatial working memory task was designed to be the non-spatial equivalent of the radial maze. Search paths recorded on the first trial of the Invisible Sensor Task, when subjects search for the target by trial and error are reported. An analysis of the search paths revealed that patients with lesions to the right or left hippocampus or parahippocampal cortex employed the same type of search strategies as normal controls did, showing similarities and differences to the search behavior recorded in rats. Interestingly, patients with lesions that included the right parahippocampal cortex were impaired relative to patients with lesions to the right hippocampus that spared the parahippocampal cortex, when recall of the sensor was tested after a 30 min delay (Bohbot et al. 1998). No differences were obtained between control subjects and patients with selective thermal lesions to the medial temporal lobe, when tested on the radial-maze, the non-spatial analogue to the radial-maze and the path integration tasks. Differences in methodological procedures, learning strategies and lesion location could account for some of the discrepant results between humans and non-human species. Patients with lesions to the right hippocampus, irrespective of whether the right parahippocampal cortex was spared or damaged, had difficulties remembering the particular configuration and identity of objects in the novelty detection of the object location task. This supports the role of the human right hippocampus for spatial memory, in this case, involving memory for the location of elements in the room; learning known to require the hippocampus in the rat.

Ant odometry in the third dimension.

Desert ants (Cataglyphis) are renowned for their ability to perform large-scale foraging excursions and then return to the nest by path integration. They do so by integrating courses steered and the distances travelled into a continually updated home vector. Whereas the angular orientation is based on skylight cues, how the ants gauge the distances travelled has remained largely unclear. Furthermore, almost all studies on path integration in Cataglyphis, as well as in spiders, rodents, and humans, have aimed at understanding how the animals compute homebound courses in the horizontal plane. Here, we investigate for the first time how an animal's odometer operates when a path integration task has to be accomplished that includes a vertical component. We trained Cataglyphis ants within arrays of uphill and downhill channels, and later tested them on flat terrain, or vice versa. In all these cases, the ants indicated homing distances that corresponded not to the distances actually travelled but to the ground distances; that is, to the sum of the horizontal projections of the uphill and downhill segments of the ants' paths.