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The Brain as a Supervenience Hierarchy: A Reinterpretation of 'Control' and Function
In the model presented here, the brain is organised as a supervenience hierarchy, where higher levels of organisation emerge from the interactions at lower levels during development and experience. Crucially, there is no direct interaction between these levels. Higher levels of organisation do not "control" lower levels—a concept often referred to as "downward causation"—any more than a clock controls the molecules it supervenes upon as a level of organisation. Both higher and lower levels of organisation provide complementary perspectives on the same underlying phenomenon, rather than representing a relationship of control.
This interpretation challenges traditional notions of control in neurological systems. On the Theory of Neuronal Group Selection (TNGS) model, the idea of control is better understood in terms of selectional interaction between systems within the same level of organisation, rather than imposing a hierarchy of control across organisational levels. The suggestion that higher levels exert downward control over lower levels represents a category error: applying a hierarchy of control to a hierarchy of organisational levels distorts the nature of how systems interact within those levels.
When we consider interactions at the same level of organisation, each system is necessary for the function it performs, but not sufficient in isolation. For example, a gene associated with iris colour is necessary but not sufficient for the expression of that colour in a phenotype. Its function is dependent on the context provided by other genes and their own functions within the broader genetic system. The same principle applies to neurological functions: they are carried out within the context of other functions, and each function is distinguished by its relationship to other functions within the network. The absence or disruption of a specific function is due to the absence or disruption of a necessary condition for its performance, much like the absence or mutation of a gene alters its phenotypic expression.
Some have argued that specific brain functions are localised to certain anatomical areas, based on the idea that the presence or absence of brain activity in those areas directly corresponds to the presence or absence of function. However, neuro-imaging studies demonstrate that even simple tasks, such as reciting digits, involve the activation of multiple brain regions. The precise locations of this neural activity can vary between individuals, challenging the notion that specific brain functions are exclusively confined to distinct anatomical regions. The brain's functioning is thus distributed and dynamic, and its organisation should be understood not in terms of rigid localisation, but as a complex interplay of systems interacting at multiple levels.