This paper studies the behavior of a large body of neurons in the cont
inuum limit. A mathematical characterization of such systems is obtain
ed by approximating the inverse input-output nonlinearity of a cell (o
r an assembly of cells) by three adjustable linearized sections. The a
ssociative spatio-temporal patterns for storage in the neural system a
re obtained by using approaches analogous to solving space-time field
equations in physics. A noise-reducing equation is also derived from t
his neural model. In addition, conditions that make a noisy pattern re
trievable are identified. Based on these analyses, a visual cortex mod
el is proposed and an exact characterization of the patterns that are
storable in this cortex is obtained. Furthermore, we show that this mo
del achieves pattern association that is invariant to scaling, transla
tion rotation and mirror-reflection.