The lost ability to find the way: Topographical disorientation after a left brain lesion

摘要

Objective: We report the case of a patient (M.S.) who, after a left brain damage in posteromedial areas, showed a deficit in determining the direction of any destination with respect to his current position or to external frames (heading disorientation). Given that spatial cognition includes a wide range of cooperating abilities, we deemed that M.S.'s spatial disorientation could be ascribed to specific alterations within this multicomponent system where landmarks and spatial frames of reference contribute to organize information for different purposes. Method: M.S. and 12 healthy elderly people (NCs) were submitted to an extensive neuropsychological assessment and to 2 ad hoc spatial tasks: (a) Object-Location Memory Task (what, where, and their binding); and (b) spatial memory task combining categorical (nonmetric)/coordinate (metric) relations with egocentric/allocentric frames of reference (in verbal and visuomotor conditions). Results: M.S.'s performance was compared with that of NCs by means of a modified t test to small control sample size. M.S. met difficulty in positional processing and binding but not in object recognition. M.S. showed a selective deficit in the coordinate component in verbal (combined with both egocentric and allocentric frames) and visuomotor (only with the egocentric frame) spatial judgment tasks. In contrast, the categorical component looked always preserved in both frames of reference. Conclusions: The left posteromedial brain areas contribute in combining and translating metric relations according to frames of reference and in using these representations to guide actions according to an egocentric perspective.