The supposed link is that being a successful cab driver requires you to memorize a lot of street names and layouts, and if you do that for long enough it makes your hippocampus huge and beefy:

> According to a small brain-imaging study published in 2000, London cab drivers had unusually large hippocampi. This part of the brain also happens to degrade in people with Alzheimer’s disease.

[...]

> Interestingly, taxi drivers are not known for stellar health outcomes, Jena says. They typically have higher mortality rates compared with people in other occupations, making their very low Alzheimer’s rates especially remarkable. The researchers wondered if taxi drivers experience other factors that protect them against dementia more generally. In that case, the researchers would expect cab and ambulance drivers to be similarly protected from other types of dementia as well. But their analysis showed these drivers had ordinary rates of vascular dementia, which does not involve the hippocampus.

> And the very low incidence of Alzheimer’s disease did not manifest among drivers of other modes of transportation, which involve “fewer navigational demands.” Another brain-imaging study of long-time London bus drivers found that they do not have enlarged hippocampi. Scientists suspect that this is because “bus drivers are driving predetermined routes,” says Jena. “It’s not this on-the-fly navigational memory that taxi drivers are required to possess.” He and his colleagues found that pilots and ship captains also exhibited typical rates of Alzheimer’s mortality.

https://www.harvardmagazine.com/2025/05/harvard-taxi-drivers...