William H. Calvin is a professor emeritus of neurophysiology at the University of Washington in Seattle. He studies neuroscience and evolutionary biology following the ideas of neural Darwinism, the biological, and more specifically Darwinian and selectionist, approach to understanding global brain function.

Neural Darwinism was first proposed by American biologist and Nobel-Prize recipient Gerald Edelman in his 1987 book of the same name Neural Darwinism – The Theory of Neuronal Group Selection.

But Neural Darwinism theory goes back to Edelman and Vernon Mountcastle's 1978 book, The Mindful Brain – Cortical Organization and the Group-selective Theory of Higher Brain Function, which describes the columnar structure of the cortical groups within the neocortex. Mountcastle described them as "minicolumns."

Calvin visualizes the cortical minicolumns as patterns which he calls the "cerebral codes."

In particular, we need to know about the cerebral codes those patterns that represent each of the words of our vocabulary, and so forth - and what creates them. At first, it appears that we are dealing with a four-dimensional pattern - the active neurons scattered through three-dimensional cortex, as they perform in time. But largely because the minicolumns seem to organize all the cortical layer around similar interests, most people working on cortex think of it as a two-dimensional sheet rather like the retina (yes, the retina is 0.3 mm thick and is subdivided into a few layers, but the mapping is clearly for a two-dimensional image).

So we can try thinking of two dimensions, plus time, for cortex [which is, of course, the way we apprehend the images on a movie screen or computur terrninal] -perhaps with transparent overlays when the different cortical layers do different things. Just imagine the human cortex flattened out on those four sheets of typing paper like pie crust. with little patches lighting up like message-board pixels. What patterns will we observe when that cortex is seeing a comb? When the word "comb" is heard, or said? When the cortex is commanding a hand to comb the hair?

When Calvin describes memory as resembling the firing sequence at input to memory, i.e., in a "Hebbian assembly," he is close to our ERR model of the mind. But we do not see the neurons as a "representation of words," as he does.

Memory recall may consist of the creation of a spatiotemporal sequence of neuron firings - probably a sequence similar to the firing sequence at the time of the input to memory. but shorn of some of the nonessential frills that promoted it. The recalled spatioternporal pattern would be something like a message board in a stadium, with lots of little lights flashing on and off, creating an overall pallern. A somewhar more general version of such a Hebbian cell assembly would avoid anchoring the spatiotemporal pattern to particular cells, to make it more like the way the message board can scroll. The pattern continues to mean the same thing, even when it's implemented by different lights.

How Brains Work, p.121

Calvin proposed his own "major transitions" as a modified version of those by John Maynard-Smith and Eörs Szathmáry.