1.1 Overview We are living in a decade recently declared as the "Decade
of the Brain". Neuroscientists may soon manage to work out a functional
map of the brain, thanks to technologies that open windows on the mind.
With the average human brain consisting of 15 billion neurons, roughly
equal to the number of stars in our milky way, each receiving signals
through as many as 10,000 synapses, it is quite a view. "The brain is
the last and greatest biological frontier", says James Weston
codiscoverer of DNA, considered to be the most complex piece of
biological machinery on earth. After many years of research by
neuroanatomists and neurophys- iologists, the overall organization of
the brain is well understood, but many of its detailed neural mechanisms
remain to be decoded. In order to understand the functioning of the
brain, neurobiologists have taken a bottom-up approach of studying the
stimulus-response characteristics of single neurons and networks of
neurons, while psy- chologists have taken a top-down approach of
studying brain func- tions from the cognitive and behavioral level.
While these two ap- proaches are gradually converging, it is generally
accepted that it may take another fifty years before we achieve a solid
microscopic, intermediate, and macroscopic understanding of brain.