[chris (OP)]

Margaret has asked:

I understand that people who suffer recurrent severe depression have smaller hippocampuses (hippocampi ?) and that London cabbies, who have to learn and navigate streets of London, have larger ones. 

My question is "Do London cabbies suffer from depression ?"

[chris (OP)]

I'm not aware of any data suggesting that cab driving is protective against depression. However, what is interesting is the reference you make to the size of the hippocampus. As Eleanor Maguire famously showed in 2000, London taxi drivers have a larger hippocampus by volume compared with the population average (http://www.pnas.org/content/97/8/4398.short).

For a while no one was sure whether this was cause, or effect. However, a subsequent follow-up study in 2011 showed that the process of learning the streets of London did indeed seem to lead to the increase in hippocampal size (http://www.cell.com/current-biology/fulltext/S0960-9822(11)01267-X?_returnURL=http%3A%2F%2Flinkinghub.elsevier.com%2Fretrieve%2Fpii%2FS096098221101267X%3Fshowall%3Dtrue), suggesting that this appears to be a reactive change.

This is achieved, we think, through the birth of new neurones in the brain substance close to the hippocampus. These neurones can be integrated into the hippocampal circuitry, although the numbers that survive long-term does vary. Now we know that depression reduces the likelihood of the persistence of these newborn cells while exercise, antidepressants and sex increases the chance.

Taxi drivers are probably more likely to be successful in passing the knowledge and gaining their taxi-license if they have the capacity to grow their hippocampus in the first place - by not being depressed. Thus I think it's more likely that taxi drivers will not be depressed, but not because they have a bigger hippocampus: instead, they have the capacity to develop a bigger hippocampus because they are not depressed!

[Colin2B]

......while exercise, antidepressants and sex increases the chance.

So, if they are not depressed and taking antidepressants, and they don't get much exercise in their job, they must be gettting more sex?

[chris (OP)]

There are various stereotypes regarding minicab drivers to whom your claim may apply, but they are not the same as proper London cabbies who are paid-up professionals. You've made a bit of a jump in your logic though. I said that the three factors - exercise, antidepressants and sex - can shift the proportion of cells that survive; I didn't say that without these factors none survive! If the cabbies were indulging in the aforementioned, perhaps their ability to marshall geospatial information would be further enhanced. Perhaps this is what minicab drivers are subconsciously doing?!

[alancalverd]

Darwin at work here, I think.

The Knowledge generally requires at least 3 years of study and plying the routes on a moped in all weathers, interspersed with umpteen written and oral examinations on all aspects of professional driving as well as some 300 routes and 3000 named destinations.

Anyone prone to depression would be weeded out at the first oral exam!