A new study published today in the journal Nature Communications reveals some of the drawbacks of using satellite navigation (SatNav) technology. After scanning the brains of 24 volunteers as they explored a simulation through the streets of London's Soho district, researchers from the University of London found that listening to a satellite navigation's instructions "switches off" activity in parts of the brain used for navigation. Scientific American reports: The researchers found that a brain structure called the hippocampus, which is involved in both memory and spatial navigation, appears to encode two different maps of the environment: One tracks the distance to the final destination as the crow flies and is encoded by the frontal region of the hippocampus, the other tracks the "true path" to the goal and is encoded by its rear region. During the navigation tasks, the hippocampus acts like a flexible guidance system, flipping between these two maps according to changing demands. Activity in the hippocampal rear region acts like a homing signal, increasing as the goal gets closer. Analysis of the brain-scanning data revealed activity in the rear right of the hippocampus increased whenever the participants entered a new street while navigating. It also varied with the number of new path options available. The more alternatives there were, the greater the brain activity. The researchers also found that activity in the front of the hippocampus was associated with a property called centrality, defined by the proximity of each new street to the center of the network. Further, they observed activity in the participants' prefrontal cortices when they were forced to make a detour and had to replan their route -- and this, too, increased in relation to the number of options available. Intriguingly, when participants followed SatNav instructions, however, brain activity in these regions "switched off." Together, the new findings suggest the rear portion of the hippocampus reactivates spatial memories of possible navigation paths, with more available paths evoking more activity, and that the prefrontal cortex may contribute to path-planning by searching though different route options and selecting the best one.