Explanations of Results: Maguire et al. argue that this study demonstrates the plasticity of the hippocampus in response to environmental demands. They argue that the posterior hippocampus stores a spatial representation of the environment and that in the London taxi drivers the volume of the posterior hippocampus expanded because of their dependence on navigation skills. The authors believe that this study suggest that the changes in hippocampal gray matter—at least on the right—are acquired. This finding indicates the possibility of local plasticity in the structure of the healthy adult human brain as a function of increasing exposure to an environmental stimulus. Maguire et al. argue that the anterior and posterior hippocampus have different roles. The posterior hippocampus is involved when previously learned spatial information is used, whereas the anterior hippocampal region may be more involved (in combination with the posterior hippocampus) during the encoding of new environmental layouts. They also suggest that the left and right sides of hippocampus have different functions. They speculate that the right holds mental maps whereas the left hippocampus complements its partner by storing memories of people and events. The authors note that this study has implications for the rehabilitation of those who have suffered brain injury or disease. If similar environment related plasticity is possible in other regions of the human brain outside of the hippocampus then such people may be helped in the future.