For three-quarters of a century, developmental biologists have been asking
how the nervous system is specified as distinct from the rest of the ectode
rm during early development, and how it becomes subdivided initially into d
istinct regions such as forebrain, midbrain, hindbrain and spinal cord. The
two events of 'neural induction' and 'early neural patterning' seem to be
intertwined, and many models have been put forward to explain how these pro
cesses work at a molecular level. Here I consider early neural patterning a
nd discuss the evidence for and against the two most popular models propose
d for its explanation: the idea that multiple signalling centres (organizer
s) are responsible for inducing different regions of the nervous system, an
d a model first articulated by Nieuwkoop that invokes two steps (activation
/transformation) necessary for neural patterning. As recent evidence from s
everal systems challenges both models, I propose a modification of Nieuwkoo
p's model that most easily accommodates both classical and more recent data
, and end by outlining some possible directions for future research.