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.

Methods: To evaluate the efficiency of the test-battery, we tested 16 healthy subjects (20–65 years) using three simple tasks, which are considered to measure different aspects of PI and spatial memory: 1. Goal-directed walking task (GT), in which participants attempted to walk to a previously seen target. 2. Homing task (HT), in which subjects attempted to return to a starting point after being guided blindfolded a certain linear distance. 3. Homing-vector task (HVT), in which subjects were asked to complete the third side of a previously guided triangle. Subjects were blindfolded and wore earphones. Tasks were randomized and performed in a corridor of the University Hospital. To measure the subjects' three dimensional position, a Light Emitting Diode (LED)-camera tracking system was used. Raw data were analyzed by using Matlab® 7.0 software. Results focused on the correlation of required/walked distance for GT, HT, HVT and the correlation of required/walked angle (HVT).

Results: The analysis of data from healthy subjects showed that all tasks can be performed with high accuracy and reliability, the HVT being the most demanding test. Test results showed a low variability between runs (5 repetitions for each of 3 different distances in GT and HT).

Conclusion: Our data show, that this test-battery reveals results comparable to the PI performance found in previous studies. The new test-battery is a reliable diagnostic tool and can now be used for the systematic investigation of PI ability in patients with spatial memory deficits. PI so far was not tested routinely in patients and we expect new insights in the brain structures involved in human spatial orientation.