Katherine Woollett

Who they are

Woollett's research concerns hippocampal structure and spatial navigation. She is best known as first author of Woollett and Maguire (2011), the paper that moved the taxi-driver question from comparison to follow-up. The earlier 2000 study could show that licensed drivers differed from other people. It could not show which came first, the job or the difference.

In this site's citations the first author is credited, which for the 2011 paper means Woollett. Two popular books in the vault cite the study in endnotes while naming no one in the text.

Key papers

Woollett, K., & Maguire, E. A. (2011). "Acquiring 'the Knowledge' of London's layout drives structural brain changes." Current Biology, 21(24), 2109 to 2114.

The study began with 79 trainee taxi drivers, all starting the training for the London licence, known as the Knowledge, and 31 control participants who were not training. Training typically takes three to four years. Participants were scanned at the start and again after the training period. Of the trainees, 39, or 51.9 per cent, qualified.

Those 39 had more grey matter in the posterior hippocampus afterwards than they had before training. Trainees who did not qualify showed no such change, and neither did the controls. No change appeared in the anterior hippocampus. Qualified drivers also performed worse than controls on other memory tasks, such as recalling complex visual information, and trainees who failed to qualify did not show that deficit.

The paper's abstract states why a longitudinal design was needed. Cross-sectional studies linking brain structure to skills are informative, it says, but cause and effect are impossible to establish without scanning the same individuals before and after an intervention. Earlier longitudinal studies, it adds, had often involved children or young adults, whose brains are also developing, had mostly been restricted to the motor domain, and had run for weeks or months. The taxi trainees were average-IQ adults learning a complex real-world task over about four years. The authors concluded that specific, enduring structural change can be induced in adult humans by behaviours that engage higher cognitive functions such as spatial memory.

Key ideas

Three comparisons in one study. The design carries three checks. Each qualified trainee is compared with their own earlier scan. Qualified trainees are compared with trainees who did not qualify. Both are compared with controls who did not train. A change that appears only in the qualified group, and is absent in the failed group and the controls, is hard to attribute to age, to being scanned twice or to the general fact of starting a demanding course.

Why the failed trainees matter. The group that did not qualify answers an objection the 2000 paper could not: that people with larger posterior hippocampi simply choose or survive the job. If that were the whole story, the larger hippocampi would have been present before training and would not have grown. The 2011 result is a change within the same people.

A slow, specific effect. The training took three to four years and the change sat in a named region. The result does not describe an effect of weeks, and it does not describe one in a general population. For anyone reading a product claim that cites plasticity, the useful comparison is the dose: years of effort on one demanding task.

The trade-off. The memory cost in qualified drivers is the least quoted part of the paper. It shows that what the training bought was specialised, and that specialisation was not free.

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