Heading disorientation: a new test and a possible underlying mechanism.

BACKGROUND/AIMS: Heading disorientation (HD) is a type of pure topographical disorientation. Reported cases showing HD have been very few so far, and its underlying mechanism remains unclear. The aim of this study is to find the anatomic substrates of HD and to demonstrate a possible underlying mechanism for the symptom.

METHODS

We investigated 3 patients with HD by a new test, the card-placing test (CPT). Part A of the test assesses the ability of a subject to retain information on spatial locations of cards placed on the floor around the subject. Part B examines the subject's ability to integrate information on the spatial locations of similarly arranged cards and that on changes of the body directions.

RESULTS

The patients had a lesion that commonly involved the right retrosplenial cortex and showed good record results for part A but very poor ones for part B.

CONCLUSIONS

The results of the CPT suggest that HD patients cannot integrate information on the spatial locations of objects derived from an egocentric reference frame with that on changes of the body directions. The retrosplenial cortex may be the place where these different types of information necessary for navigation converge.