Neural basis of mental scanning of a topographic representation built from a text.

Humans have the ability to build and to inspect an internal visual image of an environment built from a verbal description. We used positron emission tomography (PET) to investigate the brain areas engaged in the mental scanning of a map that subjects built from the reading of a descriptive text. This task engaged a parieto-frontal network known to deal with spatial representations. Additional activations were evidenced in the angular gyrus and in Broca's and Wernicke's areas. In order to examine the neural impact of the learning modality, these PET results were compared to those obtained in another group of six subjects who performed a similar mental scanning task on a topographic representation built from visual inspection of a map. Both scanning tasks engaged the parieto-frontal network. However, the bilateral activation of the angular gyrus as well as the involvement of language areas appeared specific to the mental scanning of the topographic representation built from textual information. On the other hand, the right medial temporal lobe was activated only when a map had been visually learned. These results suggest that although both tasks involved visuo-spatial internal representation, a trace of the learning modality remained present in the brain.