Easy problems and the hard one
In 1995 the philosopher David Chalmers split the question of consciousness in two (Journal of Consciousness Studies 2, 200).
The easy problems are about functions: how the brain tells red from green, integrates signals, focuses attention and reports "I see red". They are difficult, and neuroscience makes steady progress on them.
The hard problem is why any of this is accompanied by experience, why there is something it is like to see red. You could, in principle, explain every function and still not have explained that.
Some philosophers (Daniel Dennett, Keith Frankish) argue that the hard problem dissolves once the functions are explained, and that the sense of an extra ingredient is an illusion the brain produces. Others think it points to a gap in physics itself. That disagreement is still open.
The main theories, briefly
Global workspace theory (Bernard Baars, 1988; Stanislas Dehaene and colleagues). Information becomes conscious when it wins a competition and is broadcast across a brain-wide network, so that many systems can use it at once. It predicts a sudden "ignition" of frontal and parietal activity when a stimulus becomes conscious.
Integrated information theory, IIT (Giulio Tononi, 2004). Consciousness is integrated information, measured by a quantity Φ: how much a system as a whole constrains its own past and future beyond its parts. It predicts that consciousness depends on the causal structure of posterior cortex more than on frontal broadcast. A practical offshoot, the perturbational complexity index (Casali et al., 2013), distinguishes wakefulness, sleep, anaesthesia and disorders of consciousness from EEG responses to magnetic pulses.
Higher-order theories (David Rosenthal and others). A state is conscious when the brain represents itself as being in that state.
Predictive processing (Andy Clark, Anil Seth, Karl Friston). The brain is a prediction machine; experience is the content of its best guesses about the world and the body.
Orch-OR (Roger Penrose and Stuart Hameroff, 1996). Consciousness arises from quantum processes in neuronal microtubules. It is the most physics-heavy proposal and the most disputed.
What the head-to-head tests found
A consortium of labs (Cogitate) ran preregistered experiments designed so that GWT and IIT would predict different results. The findings, released in 2023 and published in Nature in 2025, supported some predictions of each theory and contradicted others: the sustained synchronisation within posterior cortex that IIT predicted did not appear, and neither did the "ignition" at stimulus offset that GWT predicted.
The lasting lesson is methodological. Theories of consciousness are now judged by preregistered predictions that can fail. That shift matters more than any single result.
Where the information-architecture view fits
The research programme on this site treats consciousness as a problem about how information is addressed and read, not only how much of it is integrated. In that picture, a conscious system is one that reads from and writes to a shared structure beyond its own parts, a pattern the programme calls Pointer Architecture and implements as working code (the Sixth language) with a substrate-side consciousness measure, Φ_PA.
For consciousness, the view makes one risky prediction, discussed in the essay Attention as load: if attention is a read operation on a shared structure, mass focused attention should have a small, measurable effect on physical random processes under a preregistered protocol. Earlier experiments of this kind (PEAR, the Global Consciousness Project) produced small, contested effects. A clean null result under a strict protocol would count against the idea.
Bottom line
Science has good and improving theories of which brain processes are conscious. None has closed the hard problem. Theories now compete on testable predictions, and any serious new proposal, including this programme's, has to be judged the same way.