Driving a taxi is a brain disease

Maguire, E. et al., Navigation-related structural change in the
hippocampi of taxi drivers, PNAS, 2000
http://www.pnas.org/content/97/8/4398.full

"Taxi drivers had a significantly greater volume in the posterior
hippocampus, whereas control subjects showed greater volume in the
anterior hippocampus."

The author's question the possiblity that the result is caused by people
fitting a role rather than the occupation changing the brain structure
of the individual.
" For example, could this particular arrangement of hippocampal gray
matter predispose individuals to professional dependence on navigational
skills?"

However they say
"We believe that these data suggest that the changes in hippocampal gray
matter—at least on the right—are acquired. As such, 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."

They go on to say
"Our results suggest that the "mental map" of the city is stored in the
posterior hippocampus and is accommodated by an increase in tissue
volume. These results challenge the traditional view that the
hippocampus has a transient role in memory at least in relation to
spatial navigation and the posterior hippocampus."

And conclude
"The differential changes in posterior and anterior hippocampus may
represent two separate processes. The most parsimonious explanation,
however, is that our findings reflect an overall internal reorganization
of hippocampal circuitry (34 <#ref-34>) in response to a need to store
an increasingly detailed spatial representation, where changes in one
hippocampal region are very likely to affect others. On a broader level,
the demonstration that normal activities can induce changes in the
relative volume of gray matter in the brain has obvious implications for
rehabilitation of those who have suffered brain injury or disease. It
remains to be seen whether similar environment-related plasticity is
possible in other regions of the human brain outside of the hippocampus."

So in short there is a degree of change possible in adult brains through
environmental factors. The reason I've titled this piece "Driving a taxi
is a brain disease" is because this sort of research into children with
schziophrenia (highlighted in an earlier blog post) is interpreted to
justify schizophrenia as a brain disease. The same reasoning could be
applied to this study. This study shows that there is a reduction and a
swelling in grey matter caused by prolonged taxi driving. The small
amount of neurobiological schizophrenia research I've seen so far
targets areas of the brain where there is an expected reduction in grey
and/or white matter however perhaps global studies of the brain will
show that other areas swell or grow while the well-studied areas shrink.

Given the considerably higher level of plasticity in the developing
child brain it is highly possible that the effects seen in early-onset
schizophrenia are, in fact, the results of the psychosocial impact of
madness rather than any degenerative neurological illness.

I must admit my knowledge of neuroscience is currently limited and I may
be misinterpreting the results of this study, or perhaps not.