A new study found that at the beginning of a journey, one region of the brain calculates the straight line to the destination — the distance “as the crow flies” — but during travel a different area of the brain computes the precise distance along the path to get there.
The findings upend previous thinking, which was that the brain either calculates a route or calculates the straight line to a destination. By showing that the brain does both, the new study shows that not only are both ideas correct, but the two should be integrated.
For the study, published in Current Biology, Dr. Hugo Spiers and his research team at University College London used film footage to recreate the busy streets of Soho in London inside an MRI scanner. Volunteers were asked to navigate through the district, famous for its winding roads and complex junctions, while their brain activity was monitored.
The researchers then analyzed brain activity during the different stages of the journey: Setting course for the destination, keeping track of the destination while traveling, and decision-making at street junctions.
The researchers found that activity in the entorhinal cortex, a region essential for navigation and memory, was sensitive to the straight-line distance to the destination when first working out how to get there.
By contrast, during the rest of the journey, the posterior hippocampus, also famous for its role in navigation and memory, became active when keeping track of the path needed to reach the destination, the researchers reported.
The results also revealed what happens in the brain when we use satellite navigation (Sat Nav) or a handheld GPS to get to a destination. By recording brain activity when participants used Sat Nav-like instructions, the researchers found that neither of the brain regions tracked the distance to the destination and, in general, the brain was much less active.
“Our team developed a new strategy for testing navigation and found that the way our brain directs our navigation is more complex than we imagined, calculating two types of distance in separate areas of the brain,” Spiers said.
“These findings help us understand the mechanisms by which the hippocampus and entorhinal cortex guide navigation. The research is also a substantial step towards understanding how we use our brain in real world environments, of which we currently know very little.”
The results also might explain why London taxi drivers famously end up with an enlarged posterior hippocampus, he noted.
“Our results indicate that it is the daily demand on processing paths in their posterior hippocampus that leads to the impressive expansion in their grey matter,” he explained.
The findings also provide insight into the underlying biology of mental health conditions that affect memory, according to Dr. John Williams, head of clinical activities, neuroscience and mental health at the Wellcome Trust, which funded the study.
“The hippocampus and entorhinal cortex are among the first regions to be damaged in the dementia associated with Alzheimer’s disease and these results provide some explanation as to why such patients struggle to find their way and become lost,” he said. “Combining these findings with clinical work could enable medical benefits in the future.”
Source: Wellcome Trust