HOW THE BRAIN MAKES POTENTIAL 197ize a detailed map of London streets. It becomes refl ected in an increased
size (presumably network expansion) of part of the brain, the hippocam-
pus, involved in memory formation. Violin players have been found to
have enlarged parts of the brain to do with fi ne motor coordination on one
side but not on the other side. In circus jugglers, three months of train-
ing was refl ected in gray matter macrostructure in cortica l areas. Increases
in brain network size even seem to correlate with the numbers of words
we learn, at least in adolescence: again diff erences from the outside in,
rather than inside out.^41
Th ere are many other examples. In a wide- ranging review, Arne May
described the phenomenon as follows: “Contrary to assumptions that
changes in brain networks are pos si ble only during crucial periods of
development, research in the past de cade has supported the idea of a
permanently plastic brain. Novel experience... environmental changes
and learning new skills are now recognized as modulators of brain func-
tion and under lying neuroanatomic circuitry.”^42 Th e implication is that,
whereas the brain- IQ correlations reported from MRI scans have been
invariably interpreted as causal, in one direction, the causal eff ect, if any,
may really be in the opposite direction.
May also points to “fi ndings in experiments with animals and the re-
cent discovery of increases in gray and white matter in the adult human
brain as a result of learning” and concludes that “understanding norma-
tive changes in brain structure that occur as a result of environmental
changes and demands is pivotal to understanding the characteristic
ability of the brain to adapt.”^43
It has also been demonstrated in monkeys, as well as in simulations
using artifi cial networks, that the existing state of a network can con-
strain new learning if it is based on an unfamiliar kind of structure. In
other words, the current state of brain development will have some infl u-
ence on ease of learning from new experiences until some catch-up has
taken place.
Attempting to describe brain diff erences in terms of a single over-
arching speed, or other mechanical function, therefore, is pointless. Like
physiology and epige ne tics, it is more accurate to describe what the brain
does as a cooperative interaction among numerous subfunctions. Nor
should we forget how ner vous systems are closely interrelated with other
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