Our increasing knowledge of 
the working of the visual cortex 
has come from a combination of 
strategies. Even in the late 
1950s, the physiological method 
of recording from single cells 
was starting to tell us roughly 
what the cells were doing in 
the daily life of an animal, at a 
time when little progress was 
being made in the detailed 
wiring diagram. In the past few 
decades both fields, physiology 
and anatomy, have gone ahead 
in parallel, each borrowing 
techniques and using new 
information from the other.

    I have sometimes heard it 
said that the nervous system 
consists of huge numbers of 
random connections. Although 
its orderliness is indeed not 
always obvious, I nevertheless 
suspect that those who speak of 
random networks in the 
nervous system are not 
constrained by any previous 
exposure to neuroanatomy. 
Even a glance at a book such as 
Cajal's Histologie du Système 
Nerveux should be enough to 
convince anyone that the 
enormous complexity of the 
nervous system is almost always 
accompanied by a compelling 
degree of orderliness. When we 
look at the orderly arrays of 
cells in the brain, the 
impression is the same as when 
we look at a telephone 
exchange, a printing press, or 
the inside of a TV set--that the 
orderliness surely serves some 
purpose. When confronted with 
a human invention, we have 
little doubt that the whole 
machine and its separate parts 
have understandable functions. 
To understand them we need 
only read a set of instructions. 
In biology we develop a similar 
faith in the functional validity 
and even ultimately in the 
understandability of structures 
that were not invented, but 
were perfected through 
millions of years of evolution. 
The problem of the 
neurobiologist (to be sure, not 
the only problem) is to learn 
how the order and complexity 
relate to the function.

    To begin, I want to give you a 
simplified view of what the 
nervous system is like--how it 
is built up, the way it works, 
and how we go about studying it. 
I will describe typical nerve 
cells and the structures that 
are built from them.