Assessment of Topographical Disorientation: First Application of New Tests and Case Report.

A right posterior cerebral lesion can lead to an inability to orient and can consequently interfere with daily-life autonomy. Despite the wide literature about navigation abilities, it is still difficult to assess topographical disorientation (TD) because of the interindividual specificity of spatial knowledge and the diversity of symptoms. We describe here a set of new tests evaluating spatial cognition in a patient with TD presenting difficulties in navigating inside the hospital and in his hometown more than 3 years after his diffuse ischemic right Sylvian stroke. These tests assess mental imagery (global and specifically spatial imagery), perspective change, and the ability to recall spatial relations in familiar environments. The evaluation revealed difficulties with all the tests (but not in global mental imagery) in this patient when compared with matched controls. Hence, these new tests seem specific and affected by a right hemispheric lesion. The observed deficits can explain, at least partially, the spatial orientation difficulties experienced by this patient in the hospital and familiar environments. In conclusion, these tests could be appropriate tools for the assessment of visuospatial and spatial processes.

Segregated processing of auditory motion and auditory location: an ERP mapping study.

Recent studies have revealed a distinct cortical network activated during the analysis of sounds' spatial properties. Whether common brain regions in this auditory where pathway are involved in both auditory motion and location processing is unresolved. We investigated this question with multichannel auditory evoked potentials (AEPs) in 11 subjects. Stimuli were binaural 500-ms white noise bursts. Interaural time differences (ITD) created the sensation of moving or stationary sounds within each auditory hemifield, and subjects discriminated either their position or direction of motion in a blocked design. Scalp potential distributions (AEP maps) differentiated electric field configurations across stimulus classes. The initial approximately 250-ms poststimulus yielded common topographies for both stimulus classes and hemifields. After approximately 250-ms, moving and stationary sounds engaged distinct cortical networks at two time periods, again with no differences observed between hemifields. The first ( approximately 250- to 350-ms poststimulus onset) was during stimulus presentation, and the second ( approximately 550- to 900-ms poststimulus onset) occurred after stimulus offset. Distributed linear inverse solutions of the maps over the 250- to 350-ms time period revealed not only bilateral inferior frontal activation for both types of auditory spatial processing, but also strong right inferior parietal activation in the case of auditory motion discrimination. During the later 550-to 900-ms time period, right inferior parietal and bilateral inferior frontal activity was again observed for moving sounds, whereas strong bilateral superior frontal activity was seen in the case of stationary sounds. Collectively, the evidence supports the existence of partly segregated networks within the auditory where pathway for auditory location and auditory motion processing.