HOW THE BRAIN MAKES POTENTIAL 185views, tactile exploration while seeing) has the very purpose of collecting
sample correlations. Th is is because of the predictability they aff ord. Even
very simple exploratory probing of the environment by a fi ngertip reveals
spatiotemporal correlations, including between those emanating from
the surface and the exploratory motor action. Th ese will be complex cor-
relations as explained earlier: spatiotemporal, like music and dance, and
conditioned by other variables and correlations at deeper levels. Th ey will
be more or less matched to the structural grammars (or attractor basins)
developed from previous experience. Th en whole mental pictures or
scenes can be created from a few relational samples. Th ese, in turn, be-
come the fodder of cognition, as explained in chapter 7.BRAIN DEVELOPMENT: STRUCTURED PLASTICITYAs mentioned in chapter 5, brain cells and their elaborate networks
appear almost magically during a brief period of embryonic development.
Th e complexity of the pro cess is truly remarkable. Brain cells (neurons)
are produced in the embryo/fetus at a rate of up to 250,000 a minute.
Th ese progenitor cells not only diff erentiate into the many types of
immature neurons. Th ey also migrate over extremely long distances to
fi nd their correct positions, oft en in precise layers, at the correct time, in
the three- dimensional structure of the brain. Th en they have to produce
the thousands of pro cesses through which they interconnect. Axons em-
anating from a cell of around a thousandth of a millimeter in dia meter
may travel up to a meter to reach other cells in precise locations, oft en on
distinct layers. Th ey may be doing this alongside dozens or hundreds of
other axon terminals from other neurons (fi gure 6.2).
In mammals, especially primates, much of this occurs in the uterus
before precise sensory experience. But it is also known that spontaneous
signaling activity between neurons is needed for connections to begin to
form. By being structured, they also help structure basic connectivity. For
example, very early spontaneous signals from the ret ina are correlated in
time and space, as if setting up the brain for the deeper structures to fol-
low in real experience. Injection of drugs that inhibit such fi ring much
reduces the formation of network connections.
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