It was not always obvious that brains have much to do with thinking. Aristotle believed that the
primary organ supporting thought was the heart rather than the brain, whose main function was to cool
the blood. By the sixteenth century, however, rough connections between the brain and thinking were
generally recognized—for example, that vision and hearing depend on brain anatomy. Understanding
of how brains work began only at the end of the nineteenth century when the development of new
chemical techniques for staining cells made possible identification of the cells that constitute brains.
It was decades before the electrical nature of brain cells—neurons—was appreciated. Only with the
development of computers did it become possible to formulate and test detailed hypotheses about
how the interactions among large numbers of neurons might be able to support different kinds of
thinking.
When the psychologist Stephen Pinker was on the TV show The Colbert Report in 2007, Stephen
Colbert insisted that he explain, in five words or fewer, how the brain works. Pinker's brilliantly
concise response was “Brain cells fire in patterns.” Neurons are different from the cells that make up
other bodily organs in that they build up electrical charges; they can pass these on to other neurons
that are connected to them. Firing is a kind of electrical discharge. The flow of electrical charge in
neurons is only a few millivolts, compared to as much as a billion in lightning flashes, and also
differs in being directed along pathways formed by the thousand or so connections that a neuron has
with other neurons. These connections are called synapses. depicts how one neuron can
send messages in the form of electric signals to another neuron by means of synaptic connections