We often imagine the brain as a machine: information arrives, is processed according to established rules, and produces a response. The metaphor is useful, but it can also mislead us. It suggests a system whose organisation is fixed in advance, whose operations follow a predetermined programme.
Gerald Edelman proposed a different way of understanding the brain. Drawing on his knowledge of biological evolution, he developed what he called the Theory of Neuronal Group Selection, also known as Neural Darwinism.
The central idea was that the brain's organisation is not simply prescribed by its genetic inheritance. It develops through processes of variation and selection, both during the formation of the brain and throughout the organism's subsequent experience.
During development, the brain establishes diverse patterns of neural connectivity. This produces a repertoire of neuronal groups whose connections differ from one another. Experience then modifies the strengths of connections within and between these groups. Some patterns of connectivity become more influential; others become less so.
The process is not evolution repeated literally inside the brain. Rather, Edelman proposed that principles of variation and selection, familiar from biological evolution, could help explain how neural organisation develops and changes.
The distinction matters. A brain does not need a separate instruction for every circumstance it encounters. Its history of development and experience shapes the repertoire of responses available to it. What it can do depends partly on the organisation that has emerged through that history.
But how can diverse neural groups work together to produce coherent perception and behaviour?
Edelman's answer involved a process he called re-entry. Neural groups distributed across different brain regions continuously exchange signals through reciprocal connections. Their activity is not coordinated by a single central controller. Instead, ongoing interactions establish correlations among processes that remain distinct.
We might compare this to musicians improvising together without a predetermined score. Each responds to the others, and the coherence of their performance emerges through their continuing interaction. The analogy is imperfect, but it captures an important feature of Edelman's proposal: coordination need not depend on a central authority or a fixed plan.
Re-entry helps explain how the brain can integrate information from different sources while retaining a diversity of neural activity. The resulting organisation is neither a collection of independent processes nor a single undifferentiated whole. It is a dynamic pattern of interacting differences.
For Edelman, this biological account was essential to understanding consciousness.
Conscious experience presents us with a world that is both unified and differentiated. We experience a particular scene, rather than a collection of unrelated sensory events, yet the scene contains distinct objects, qualities and relationships. Edelman sought to understand how such experience could arise from the changing activity of a biological system.
His theory therefore directed attention away from isolated neural events towards the organisation of interacting neural populations over time. Consciousness could not be understood merely by identifying a brain region or a particular kind of neural response. The relations among neural processes mattered.
This was not yet an explanation of how biological activity becomes subjective experience. It was an attempt to establish the conditions under which consciousness could be understood as a natural phenomenon, continuous with the evolution and organisation of living systems.
The significance of Edelman's approach extends beyond its particular account of neural function. It challenges the assumption that a system's behaviour can be explained entirely by identifying its components and the rules governing each one.
The organisation of a biological system has its own history. Its present activity depends on structures shaped by earlier interactions, while its ongoing activity continues to modify the conditions of what can happen next.
The brain, on this account, is not simply a mechanism that processes the world. It is a developing organisation whose capacities emerge through its own history of interaction.
Edelman gave us a way of thinking about consciousness that began with biology rather than with an abstract problem about how matter might produce mind.
Yet one question remained. If consciousness depends on the changing interactions of diverse neural populations, what kind of organisation distinguishes the activity associated with conscious experience from other neural activity?
In their later collaboration, Edelman and Giulio Tononi would pursue this question through the idea of a dynamic core: a neural process combining integration with a diversity of possible states.
That proposal would bring them closer to an account of consciousness in terms of the organisation of neural activity. It would also provide the starting point for a subsequent development in Tononi's thinking.
The next step was to ask not only how neural processes interact, but what kind of integration could account for the unity and diversity of experience.
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