THE PHENOMENON OF BRAIN PLASTICITY 29somatosensory cortex, the area of the brain that receives haptic input from
various parts of the body, is malleable in response to changes in activity
or stimuli.^12 For example, teaching an owl monkey to use a spoon, a task
that in one experiment took about seven hundred tries for the monkey to
master, reportedly causes measurable changes in the area of the monkey’s
cortex that topographically represents (or receives information from) the
fingers (see Merzenich 2012).^13 Andy Clark (2007) sees this kind of brain
plasticity, in which new physical and mental equipment can be incorpo-
rated into the body schema, as a “profoundly embodied agency” that never
arrests (263). “Since bodily growth and change continues,” he argues, “it is
simply good design not to permanently lock in knowledge of any particular
configuration, but instead to deploy plastic neural resources and an on-
going regime of monitoring and re- calibration” (269).
Plasticity is increasingly understood as a baseline state even for adults, in
part because of neuroimaging research on experience- dependent plasticity
in adult brains. Even in this research, however, the brain does not seem to
be monolithically or globally plastic. For example, a series of studies by
Eleanor Maguire and colleagues used magnetic resonance imaging (mri)
scanning to try to measure the effect of spatial learning on the hippocam-
pus, a seahorse- shaped structure in the medial temporal lobe that in the
literature is linked to spatial memory.^14 They chose their research subjects,
London taxi drivers, because of the extensive spatial memorization re-
quired to earn a taxi license — all 25,000 streets of the city, which can take
up to four years to learn. In their first study (Maguire et al. 2000), the re-
searchers measured the volume of the hippocampus in sixteen taxi drivers
and compared it with that among a control group of non – taxi drivers. They
reported larger volume on average in the posterior area of the hippocampus
of the taxi drivers; further, each year on the job corresponded with an in-
crease in volume, which the researchers suspect is due to the reorganization
of existing cortical circuits in response to spatial learning. A second study
(Maguire et al. 2006) compared taxi drivers with bus drivers, who need
to learn far less spatial information since they follow set routes; the study
again found greater volume in the posterior hippocampi of taxi drivers.
Maguire et al. concluded, “there may be a capacity for plastic change in
the structure of the hippocampus... that can accommodate the spatial
representation of a very large and complex environment” (1091).^15 In a third