Called Path Integration Research Articles

A Neurocomputational Model of Goal-Directed Navigation in Insect-Inspired Artificial Agents.

Despite their small size, insect brains are able to produce robust and efficient navigation in complex environments. Specifically in social insects, such as ants and bees, these navigational capabilities are guided by orientation directing vectors generated by a process called path integration. During this process, they integrate compass and odometric cues to estimate their current location as a vector, called the home vector for guiding them back home on a straight path. They further acquire and retrieve path integration-based vector memories globally to the nest or based on visual landmarks. Although existing computational models reproduced similar behaviors, a neurocomputational model of vector navigation including the acquisition of vector representations has not been described before. Here we present a model of neural mechanisms in a modular closed-loop control—enabling vector navigation in artificial agents. The model consists of a path integration mechanism, reward-modulated global learning, random search, and action selection. The path integration mechanism integrates compass and odometric cues to compute a vectorial representation of the agent's current location as neural activity patterns in circular arrays. A reward-modulated learning rule enables the acquisition of vector memories by associating the local food reward with the path integration state. A motor output is computed based on the combination of vector memories and random exploration. In simulation, we show that the neural mechanisms enable robust homing and localization, even in the presence of external sensory noise. The proposed learning rules lead to goal-directed navigation and route formation performed under realistic conditions. Consequently, we provide a novel approach for vector learning and navigation in a simulated, situated agent linking behavioral observations to their possible underlying neural substrates.

Vestibular control of entorhinal cortex activity in spatial navigation.

Navigation in rodents depends on both self-motion (idiothetic) and external (allothetic) information. Idiothetic information has a predominant role when allothetic information is absent or irrelevant. The vestibular system is a major source of idiothetic information in mammals. By integrating the signals generated by angular and linear accelerations during exploration, a rat is able to generate and update a vector pointing to its starting place and to perform accurate return. This navigation strategy, called path integration, has been shown to involve a network of brain structures. Among these structures, the entorhinal cortex (EC) may play a pivotal role as suggested by lesion and electrophysiological data. In particular, it has been recently discovered that some neurons in the medial EC display multiple firing fields producing a regular grid-like pattern across the environment. Such regular activity may arise from the integration of idiothetic information. This hypothesis would be strongly strengthened if it was shown that manipulation of vestibular information interferes with grid cell activity. In the present paper we review neuroanatomical and functional evidence indicating that the vestibular system influences the activity of the brain network involved in spatial navigation. We also provide new data on the effects of reversible inactivation of the peripheral vestibular system on the EC theta rhythm. The main result is that tetrodotoxin (TTX) administration abolishes velocity-controlled theta oscillations in the EC, indicating that vestibular information is necessary for EC activity. Since recent data demonstrate that disruption of theta rhythm in the medial EC induces a disorganization of grid cell firing, our findings indicate that the integration of idiothetic information in the EC is essential to form a spatial representation of the environment.

Path integration ability in humans: establishing a new diagnostic tool

Objectives: Navigation strategies require different complex abilities. Without landmarks, navigation is based on information about self-velocity, which is transformed to position or orientation by a process called path integration (PI). Using PI, one can estimate the own position without visual or acoustic clues by integrating small increments of movement onto a continually updated representation of direction and distance from a starting point. Respective deficits can derive from damages of cerebral areas involved in spatial navigation, particularly structures of the temporal lobe, most notably the hippocampus, entorhinal cortex and parietal cortex. In this study, our aim was to establish a simple diagnostic tool to evaluate PI in patients with suspected deficits in spatial navigation.

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.

Posterior parietal rTMS disrupts human Path Integration during a vestibular navigation task

In contrast to vision, the neuro-anatomical substrates of vestibular perception are obscure. The vestibular apparati provide a head angular velocity signal allowing perception of self-motion velocity. Perceived change of angular position-in-space can also be obtained from the vestibular head velocity signal via a process called Path Integration (so-called since displacement is obtained by a mathematical temporal integration of the vestibular velocity signal). It is unknown however, if distinct cortical loci sub-serve vestibular perceptions of velocity versus displacement (i.e. Path Integration). Previous studies of human brain activity have not used head motion stimuli hence precluding localisation of vestibular cortical areas specialised for Path Integration distinct from velocity perception. We inferred vestibular cortical function by measuring the disrupting effect of repetitive transcranial magnetic stimulation on the performance of a displacement-dependent vestibular navigation task. Our data suggest that posterior parietal cortex is involved in encoding contralaterally directed vestibular-derived signals of perceived angular displacement and a similar effect was found for both hemispheres. We separately tested whether right posterior parietal cortex was involved in vestibular-sensed velocity perception but found no association. Overall, our data demonstrate that posterior parietal cortex is involved in human Path Integration but not velocity perception. We suggest that there are separate brain areas that process vestibular signals of head velocity versus those involved in Path Integration.

Noncommutative Updating of Perceived Self-Orientation in Three Dimensions

After whole body rotations around an earth-vertical axis in darkness, subjects can indicate their orientation in space with respect to their initial orientation reasonably well. This is possible because the brain is able to mathematically integrate self-velocity information provided by the vestibular system to obtain self-orientation, a process called path integration. For rotations around multiple axes, however, computations are more demanding to accurately update self-orientation with respect to space. In such a case, simple integration is no longer sufficient because of the noncommutativity of rotations. We investigated whether such updating is possible after three-dimensional whole body rotations and whether the noncommutativity of three-dimensional rotations is taken into account. The ability of ten subjects to indicate their spatial orientation in the earth-horizontal plane was tested after different rotational paths from upright to supine positions. Initial and final orientations of the subjects were the same in all cases, but the paths taken were different, and so were the angular velocities sensed by the vestibular system. The results show that seven of the ten subjects could consistently indicate their final orientation within the earth-horizontal plane. Thus perceived final orientation was independent of the path taken, i.e., the noncommutativity of rotations was taken into account.

THE WALK OF THE NAVIGATOR

Imagine you're an ant. You've run a virtual marathon from your nest in search of food and now you have to find your way home. Oh yes, and you're in a featureless desert. So, how do you do it? The answer is far from simple.Desert ants are old favourites in studies of navigation because they can navigate with amazing precision over long distances in virtually landmark-free habitats. To a large extent the ants rely on a form of navigation called path integration (PI) to find their way around when there are no landmarks to refer to. Basically, the ant keeps a running tally of all the twists and turns it makes whilst searching for food and it quickly tots up a homeward vector when it's time to return to the nest. Ants also use remembered landmarks to guide them along familiar routes. Landmark navigation tends to be more precise than path integration, so ants often use it in preference to PI when available.Matthew and Tom Collett, Stephane Chameron and Rüdiger Wehner wanted to know whether path integration and landmark-based information might interact(p. 877). Specifically they were interested in whether familiar landmarks, seen in unfamiliar positions,might reset the path integrator. This would allow the ant to recall previous PI information associated with a particular arrangement of landmarks and use it to recalibrate its path-finding system. As a result, the ant could correct any errors in its path rather like a human navigator looking at a map. Collett and his co-workers already knew that landmarks did not reset the integrator as the ant scurries home, but it might still be affected by landmarks seen as the ant searches for tasty titbits. Testing this required a bit of experimental`trickery'.Studying the ants in their natural habitat meant a trip to Tunisia, where Rüdiger Wehner and his collaborators have studied these masters of navigation for several decades. First, they trained the ants by enticing them along an L-shaped route, sunk into channels, with pieces of ripe melon. The ants couldn't see any landmarks from the first leg of the L-shaped path, but they were helped to become familiar with the second part of the route by several plastic bucket landmarks placed around the channel. Once the ants were familiar with the training route, the team altered the length of the featureless leg of the path and allowed the ants to perform a test run to the feeder.After the test run, the ants were captured when they arrived at the melon and, taken in darkness, to a bare sand test area where they were released to see which way they chose to run. If the ants were resetting their path integrator using the familiar landmarks surrounding their feeder, they would follow their usual direction to the nest. But if they calculated their homeward direction solely on the basis of the trip they had just made, using path integration alone, their heading would lead them home from the altered route.The ant's bearing matched the one required to get home from their altered test route so their path integrator was unaffected, despite the scientists attempts to deceive them with the familiar outward landmarks. The researchers concluded that the ants are blessed with two largely separate navigational systems to guide them... and by using global PI the ant can always find its way home, no matter where its search for food takes it.

Cooperation Between Dead Reckoning (Path Integration) and External Position Cues

Dead reckoning (also called path integration) is the process by which a navigating organism derives its current position relative to an Earthbound reference point from its own locomotion. Dead reckoning requires the continuous estimation of changes in direction and location through self-generated signals and the computation of position on the basis of these signals.(i) Hymenopterous insects measure rotations and translations mainly with the help of optical references such as the Sun and translational visual flow. By contrast, mammals are able to estimate their position on the basis of purely ‘internal’ information; that is, signals generated in the vestibular system by inertial forces, somatosensory feedback, and efference copies (copies of central commands that control the performance of rotations and translations). Obviously, the assessment of the angular and linear components of locomotion is much more precise if it is assisted by external references than if this is not the case.(ii) Only man-made dead reckoning systems yield precise position information through the twofold integration over time of inertial signals deriving from angular and linear acceleration. On the biological level, all species tested so far seem to rely on a simplified form of path ‘integration’: in certain test situations, arthropods and mammals (including humans) commit similar systematic errors. This suggests that species from unrelated taxa update position according to a similar algorithm.