Researchers scanned the brains of trainees before they began studying London maps and locations, a process that generally takes three to four years. "The drivers who went on to pass the exam spent twice as many hours per week training as those who failed. And when everyone turned up for the same battery of memory tests a few years later, significant differences emerged. Qualified drivers were much better than participants from the control group at judging the spatial relations between different London landmarks. But they were significantly worse at recalling the design of a complex figure drawing, suggesting that as they honed new memory skills, less useful ones deteriorated."
The researchers then returned their subjects to the MRI scanners and found that drivers who qualified exhibited increased grey matter at the back of their brains, in the hippocampus that's integral to our memory and spatial navigation skills. The finding could have greater implications beyond driving taxis, in fields like neuro-rehabilitation and adult education.