Complex sentence: There is evidence that training for the Knowledge can result in measurable physical changes in the hippocampus, the area of the brain used for spatial memory and navigation, in trainee cab drivers and the posterior hippocampus is larger in taxi drivers than in the general population.
Split into simpler sentences: There is evidence that training for the Knowledge can measurably alter the hippocampus of trainee cab drivers. The hippocampus is the area of the brain used for spatial memory and navigation, and is generally larger in taxi drivers than in the general population.