The model of brain function we will be briefly using is Gerald Edeman’s Theory Of Neuronal Group Selection. Edelman took Donald Hebb’s 1949 principle of ‘neurons that fire together, wire together’ and interpreted it in selectionist — that is: Darwinian — terms.
For present purposes, we don’t need to go into the depths of the theory, and we can just focus on one function: perceptual categorisation.
On Edelman’s (1992: 87, 125) model, perceptual categorisation involves the strengthening and weakening of synapses within neuronal groups — groups of nerve cells — in two or more functionally different (but connected) maps of neuronal groups, where each independently receiving signals from the outside world — that is, signals from sensory sheets and organs.
For example, when sensory sheets, photoreceptor cells such as the rods and cones of the retina in vertebrates, are activated, as by the impact of photons, the neuronal groups across different maps in the visual cortex that happen to be randomly firing at that time have their synapses strengthened (by the firing), and are then more likely to fire again as a discriminating combination than other neuronal groups (those that were not firing) when sensory sheets are activated again in future. These specific variants in the general population of neuronal groups have been selected in the Darwinian sense of reflecting statistical changes in populations, though here the population is of neuronal groups rather than genes.
This is, of course, oversimplifying considerably, and ignores crucial aspects such as:
the dynamics of the process, and what Edelman calls the value systems that bias the synaptic weighting process,
(Edelman’s ‘value’ refers to settings that were selected as being of adaptive value to ancestors)
but the important point here for us is that perceptual categorisation involves a correlation between specific activations of sensory sheets and activations of specific combinations of neuronal groups.
Visual perception, as in primates for example, involves a correlation between different activations of photoreceptors and different activations of specific combinations of neuronal groups in the visual cortex.