What an NCC is, and Crick and Koch's proposal
Francis Crick, co-discoverer of the structure of DNA, and the neuroscientist Christof Koch argued in 1990 that consciousness could be studied empirically rather than left to philosophy. Their strategy was to set aside the grand question of why there is any experience at all and instead hunt for the specific neural activity that reliably goes together with a particular conscious perception. They chose vision as a tractable test case and famously suggested that synchronized firing around 40 hertz might mark conscious content.
The definition that stuck is this: a neural correlate of consciousness is the minimal set of neural events and mechanisms jointly sufficient for a specific conscious experience. The word minimal matters. The whole brain is trivially sufficient for consciousness; the scientific prize is the smallest system whose activity is enough to produce a given percept.
The front-versus-back debate
A central dispute concerns where in the cortex the crucial activity lives. One camp locates the correlates toward the back of the brain, in posterior sensory and parietal regions, pointing to early signals such as a posterior negativity that tracks what people report seeing. The other camp emphasizes the front, arguing that a percept becomes conscious only when prefrontal and parietal networks broadcast it, indexed by later, widespread activation. This maps closely onto the rivalry between integrated information theory, which favors the back, and global workspace theory, which favors the front, which is why the 2025 Cogitate adversarial experiment focused on exactly this question.
Why a correlate is not yet an explanation
Finding a reliable correlate is a real achievement, but scientists and philosophers stress that correlation is not explanation. Even a perfect map of which neurons fire during a given experience would leave open why that activity is accompanied by experience at all, the issue David Chalmers named the hard problem. A further difficulty is disentangling the true correlate of an experience from its upstream causes and its downstream effects, such as attention, memory, and verbal report. No-report paradigms, which infer awareness without asking the subject to press a button, are one attempt to isolate the correlate itself. The NCC program remains the empirical backbone of consciousness science even as its interpretation stays contested.