When thousands of starlings swoop and swirl in the evening sky, creating patterns called murmurations, no single bird is choreographing this aerial ballet. Each bird follows simple rules of interaction with its closest neighbours, yet out of these local interactions emerges a complex, coordinated dance that can respond swiftly to predators and environmental changes. This same principle of emergence – where sophisticated behaviours arise not from central control but from the interactions themselves – appears across nature and human society.

Consider how market prices emerge from countless individual trading decisions, none of which alone contains the ‘right’ price. Each trader acts on partial information and personal strategies, yet their collective interaction produces a dynamic system that integrates information from across the globe. Human language evolves through a similar process of emergence. No individual or committee decides that ‘LOL’ should enter common usage or that the meaning of ‘cool’ should expand beyond temperature (even in French-speaking countries). Instead, these changes result from millions of daily linguistic interactions, with new patterns of speech bubbling up from the collective behaviour of speakers.

These examples highlight a key characteristic of highly interconnected systems: the rich interplay of constituent parts generates properties that defy reductive analysis. This principle of emergence, evident across seemingly unrelated fields, provides a powerful lens for examining one of our era’s most elusive mysteries: how the brain works.

The core idea of emergence inspired me to develop the concept I call the entangled brain: the need to understand the brain as an interactionally complex system where functions emerge from distributed, overlapping networks of regions rather than being localised to specific areas. Though the framework described here is still a minority view in neuroscience, we’re witnessing a gradual paradigm transition (rather than a revolution), with increasing numbers of researchers acknowledging the limitations of more traditional ways of thinking.

Complexity science is an interdisciplinary field that studies systems composed of many interacting components whose collective behaviours give rise to collective properties – phenomena that cannot be fully explained by analysing individual parts in isolation. These systems, such as ecosystems, economies or – as we will see – the brain, are characterised by nonlinear dynamics, adaptability, self-organisation, and networked interactions that span multiple spatial and temporal scales. Before exploring the ideas leading to the entangled brain framework, let’s revisit some of the historical developments of the field of neuroscience to set the stage.

In 1899, Cécile and Oskar Vogt, aged 24 and 29 respectively, arrived in Berlin to establish the Neurological Centre, initially a private institution for the anatomical study of the human brain that in 1902 was expanded to the Neurobiological Laboratory, and then the Kaiser Wilhelm Institute for Brain Research in 1914. Cécile Vogt was one of only two women in the entire institute. (In Prussia, until 1908, women were not granted access to regular university education, let alone the possibility to have a scientific career.) She obtained her doctoral degree from the University of Paris in 1900, while her husband Oskar obtained a doctorate for his thesis on the corpus callosum from the University of Jena in 1894.

In 1901, Korbinian Brodmann, who had concluded his doctorate in Leipzig in 1898, joined the group headed by the Vogts and was encouraged by them to undertake a systematic study of the cells of the cerebral cortex using tissue sections stained with a new cell-marking method. (The cortex is the outer brain surface with grooves and bulges; the subcortex comprises other cell masses that sit underneath.) The Vogts, and Brodmann working separately, were part of a first wave of anatomists trying to establish a complete map of the cerebral cortex, with the ultimate goal of understanding how brain structure and function are related. In a nutshell, where does a mental function such as an emotion reside in the brain?

Neurons – a key cell type of the nervous system – are diverse, and several cell classes can be determined based on both their shape and size. Researchers used these properties, as well as spatial differences in distribution and density, to define the boundaries between potential sectors. In this manner, Brodmann subdivided the cortex into approximately 50 regions (also called areas) per hemisphere. The Vogts, in contrast, thought that there might be more than 200 of them, each with its own distinguishing cytoarchitectonic pattern (that is, cell-related organisation).

It is an idea that comes close to being an axiom in biology: function is tied to structure

Brodmann’s map is the one that caught on and stuck, likely because neuroanatomists opposed too vigorous a subdivision of the cortex, and today students and researchers alike still refer to cortical parts by invoking his map. Although relatively little was known about the functions of cortical regions at the time, Brodmann believed that his partition identified ‘organs of the mind’ – he was convinced that each cortical area subserved a particular function. Indeed, when he joined the Vogts’ laboratory, they had encouraged him to try to understand the organisation of the cortex in light of their main thesis that different cytoarchitectonically defined areas are responsible for specific physiological responses and functions.

There is a deep logic that the Vogts and Brodmann were following. In fact, it is an idea that comes close to being an axiom in biology: function is tied to structure. In the case at hand, parts of the cortex that are structurally different (contain different cell types, cell arrangements, cell density, and so on) carry out different functions. In this manner, they believed they could understand how function is individuated from a detailed characterisation of the underlying microanatomy. They were in search of the functional units of the cortex – where the function could be sensory, motor, cognitive and so on.

Unlike other organs of the body that have more clear-cut boundaries, the cortex’s potential subdivisions are not readily apparent at a macroscopic level. One of the central goals of many neuroanatomists in the first half of the 20th century was to investigate such ‘organs of the mind’ (an objective that persists to this day). A corollary of this research programme was that individual brain regions – say, Brodmann’s area........

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