RECALLING ROUTES AROUND LONDON - ACTIVATION OF THE RIGHT HIPPOCAMPUS IN TAXI DRIVERS

Functional imaging to date has examined the neural basis of knowledge of spatial layouts of large-scale environments typically in the contex t of episodic memory with specific spatiotemporal references. Much hum an behavior, however, takes place in very familiar environments in whi ch knowledge of spatial layouts has entered the domain of general fact s often referred to as semantic memory. In this study, positron emissi on tomography (PET) was used to examine the neural substrates of topog raphical memory retrieval in licensed London taxi drivers of many year s experience while they recalled complex routes around the city. Compa red with baseline and other nontopographical memory tasks, this result ed in activation of a network of brain regions, including the right hi ppocampus. Recall of famous landmarks for which subjects had no knowle dge of their location within a spatial framework activated similar reg ions, except for the right hippocampus. This suggests that the hippoca mpus is involved in the processing of spatial layouts established over long time courses. The involvement of similar brain areas in routes a nd landmarks memory indicates that the topographical memory system may be primed to respond to any relevant topographical stimulation; howev er, the right hippocampus is recruited specifically for navigation in large-scale spatial environments, In contrast, nontopographical semant ic memory retrieval involved the left inferior frontal gyrus, with no change in activity in medial temporal regions.