[Neural basis of spatial orientation and memory of routes: topokinetic memory or topokinesthesic memory]

The neural basis of spatial orientation and the memory of routes have been explored by brain imaging (PET SCAN and fMRI) in human. Several cognitive strategies and several types of reference frames can be used by the brain to establish relations between our body and the environment. Four categories of brain areas have been considered: the areas involved in egocentric and allocentric coding on one hand and on the other hand the areas involved in the "route" like and the "survey or map" like strategies used during tasks in which subjects had to mentally remember a path by mental navigation or mental scanning of a map. The results have confirmed that parietal and frontal structures involved in "spatial neglect" are also found to be involved in the egocentric orientation tasks of subjective midline detection. More generally we have been able to identify parieto-frontal areas involved in visuo-spatial memory. In addition we have identified the areas involved in the cortical processing of vestibular information and lastly we have shown that in addition to the parieto-frontal areas a parieto temporal lobe network is involved in allocentric tasks and also during mental navigation by route or survey strategies. These results contribute to the identification of the neural basis of topographic memory but they also suggest that we have to define a particular type of spatial memory which is involved in the memory of routes and movements which we suggest to call "topo-kinetic" or "topo-kinesthetic" memory.