4

THE PRIMARY VISUAL CORTEX
The visual cortex in a monkey, 
stained by the Golgi method, 
shows a few pyramidal cells--a 
tiny fraction of the total 
number in such a section. The 
entire height of the photograph 
represents about 1 millimeter. A 
tungsten microelectrode, 
typical of what is used for 
extracellular recordings, has 
been superimposed, to the same 
scale.

After Kuffler's first paper on 
center-surround retinal 
ganglion cells was published in 
1952, the next steps were clear. 
To account for the properties of 
the cells, more work was 
needed at the retinal level. But 
we also needed to record from 
the next stages in the visual 
pathway, to find out how the 
brain interpreted the 
information from the eyes. Both 
projects faced formidable 
difficulties. In the case of the 
brain, some years were required 
to develop the techniques 
necessary to record from a 
single cell and observe its 
activity for many hours. It was 
even harder to learn how to 
influence that activity by 
visual stimulation.