An iconic fixture in any London street scene for decades, the black taxi cab and their extraordinary cabbies are the focal point of a new expedition into Alzheimer's research.

Cabbies have an incredible knowledge of London streets that seems to confer some protection against Alzheimer's Disease-this could be be clinically relevant to struggling patients, or those seeking to mitigate their risks.

For those on the outside, it may seem that behind the wheel of the black cabs are just regular people who help move us along to our destinations bit by bit. But hidden within their brilliant brains is a map of London's streets that for decades has put GPS technology to shame.

"The Knowledge," as it's called in the cabbie exam, was established for horse and buggy cabbies in 1865.

It stands among the hardest mental examinations one could ever undergo, as it involves the repeat retrieval from memory of minute details from between 25,000 and 56,000 London streets, depending on who's reporting, from Trafalgar Square to the tiniest residential lanes.

University College London and Alzheimer's Research UK are coming together to study the brains of these cabbies, as it's found that the hippocampus, master of the brain's short-term memory and spatial memory systems, is enlarged in the brains of cabbies.

For Alzheimer's disease, the hippocampus is the first and principal victim of its effects. Furthermore, cabbies' hippocampi continue to enlarge the more years they put into the job, presenting the hypothesis that perhaps there's something we can do to replicate the effect in the general population.

"Maybe there's something very protective about working out your spatial knowledge on a daily basis, like these guys do," said Research lead, Prof. Hugo Spiers according to Euro Weekly News.

"It may not necessarily be spatial, but just using your brain rather than Google Maps might actually help-in the same way that physical fitness is important."

At UCL's department of experimental psychology, Spiers was part of the team which 20 years ago found that, like birds and squirrels, cabbies' hippocampi gradually got bigger.

Indeed research has found for years that any animal that requires a detailed spatial knowledge of their territory experiences growth in the hippocampus, from voles to pigeons.

Alzheimer's Disease results from Tau proteins, in particular amyloid-beta, building up around the neurons in the hippocampus. Over time and in layman's terms, a brain drain occurs as the proteins interfere with the firing of neurons, leading to loss of brain tissue, and a breakdown in the critical functions of the hippocampus.

Spiers and his team hope to study the "brain gain" which occurs from putting one's powers of memory through the rigors of The Knowledge.

To glean more information on the mechanisms that cause these gains, Spiers has recruited thirty of London's cabbies to drive around on their routes hooking up to MRI machine that will allow the researchers to gather real-time observations of the workings within the hippocampus.

"It's been a joy to help [the research team] with this work and feel that I'm able to use my brain to help scientists combat dementia," said Robert Lordan, taxi driver, and author of the book The Knowledge: How to Train Your Brain like a London Cabbie. 

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