BLOBS
This cross section through the 
striate cortex shows the layers 
stained for the enzyme 
cytochrome oxidase. The darker 
zones in the upper third of the 
section are the blobs.

    By about 1978, the monkey's 
primary visual cortex, with its 
simple, complex, and end-
stopped cells and its ocular-
dominance columns and 
orientation columns, seemed 
reasonably well understood. But 
an unexpected feature of the 
physiology was that so few of 
the cells seemed to be 
interested in color. If we 
mapped a simple or complex 
cell's receptive field using 
white light and then repeated 
the mapping with colored spots 
or slits, the results as a rule 
were the same. A few cells, 
perhaps as many as a 10 percent 
of cortical upper-layer cells, 
did show unmistakable color 
preferences--with excellent 
responses to oriented slits of 
some color, most often red, and 
virtually no response to other 
wavelengths or even to white 
light. The orientation 
selectivity of these cells was 
just as high as that of cells 
lacking color selectivity. But 
most cells in the visual cortex 
did not care about color. This 
was all the more surprising 
because such a high proportion 
of cells in the lateral 
geniculate body are color coded, 
and the geniculate forms the 
main input to the visual cortex. 
It was hard to see what could 
have happened to this color 
information in the cortex.

    Suddenly, in 1978, all this 
changed. Margaret Wong-Riley, 
at the University of California 
in San Francisco, discovered 
that when she stained the 
cortex for the enzyme 
cytochrome oxidase, the upper 
layers showed an unheard of 
inhomogeneity, with periodic 
dark-staining regions, pufflike 
in transverse cross section, 
about one-quarter millimeter 
wide and one-half millimeter 
apart. All cells contain 
cytochrome oxidase, an enzyme 
involved in metabolism, and no 
one had ever imagined that a 
stain for such an enzyme would 
show anything interesting in 
the cortex. When Wong-Riley 
sent us pictures, Torsten Wiesel 
and I suspected that we were 
seeing ocular-dominance slabs 
cut in cross section and that 
the most monocular cells were 
for some reason metabolically 
more active than binocular 
cells. We put the pictures in a 
drawer and tried to forget them.