A current SciAm article, Why consciousness is the hardest problem in science, summarizes the state of the art. In a nutshell, it's stuck. There are 29 theories but we don't have technology that's sophisticated and sensitive enough to detect enough in the staggering complexity of normal brain activity. We can't tell one theory from the other. Some of the theories are backed by no experimental evidence. A unifying experimental observation and consensus belief is that, whatever it is, consciousness is very complex and is grounded in diffuse brain activity. It can't yet be pinned down to small parts of the brain.
Current thinking is that consciousness has three dimensions, all of which vary in a range of states from full off to on. The dimensions are described in the image below.
Philosophers and scientists still struggle to simply define consciousness without falling back on what it feels like to experience something. Philosophers call that “definition by pointing.” There is a way to measure an approximate degree of consciousness that expert consensus believes is real and clinically useful. The measure is called the perturbational complexity index or PCI. PCI is a crude measure of consciousness, but it reliably estimates someone’s status on the spectrum of consciousness. The SciAm article describes PCI like this:
It suggests that complexity is an important part of a conscious brain. In an awake or dreaming brain, diverse networks of neurons are in constant back-and-forth communication with one another. In this way, conscious brain activity is both differentiated (or rich in information) and integrated (forming one unified whole)—principles that Massimini borrowed from IIT, the theory that doesn’t begin with the brain. These interactions build up complexity, or what IIT theorists call a “cause-effect structure,” so that when you stimulate one part of a conscious brain, other parts respond.
But during dreamless sleep or when someone is under anesthesia, all that communication goes away. “Everything collapses,” Massimini says. “The cathedral falls apart.” Slow brain waves travel across the cortex as neurons cycle rhythmically between two electric states. In the “silent periods” between the waves, neurons enter what’s called a down state, in which they can’t respond to electric signals from their neighbors. This state is why there’s silence when you stimulate an unconscious brain with TMS: “No feedback, no unity, no complexity,” he says.
The SciAm article mentions the hostility that mainstream science still has for possible non-materialist explanations because that drifts into spiritualism/religion. After a massive study to failed to prove or disprove the leading IIT and GWT theories, some scientists got very upset. They publicly called IIT pseudoscience because they believed IIT strayed from materialism into dualism (spirituality or religion). SciAm writes:
An open letter calling IIT pseudoscience was published online in September 2023, signed by 124 researchers in or adjacent to the field. The argument focused less on the theory than on its coverage in the media, which the letter’s authors saw as credulous. The authors also took issue with the panpsychist implications of IIT, highlighting descriptions of it as unscientific and “magicalist.” “These bold claims threaten to delegitimize the scientific study of consciousness,” many of the authors wrote in a follow-up article.
The prospect that the field could lose its legitimacy hung over the fight. One side feared IIT’s reputation would drag consciousness science even further toward the fringes, and the other worried that publicly tarring one theory with a “pseudoscience” label would lead to the downfall of the entire field.
What a mess. Scientists still cannot even entertain the possibility of a partial non-physical or immaterial explanation for consciousness without the whole field getting in an uproar. Of course, the press, being the sensationalist, for profit beast it is, one can see why scientists worry about how the science related to IIT will be misunderstood and abused.
The problem is that there could still be material things we know nothing about, can't even detect yet, that could be a part of consciousness. It is still possible that the immaterial has nothing to do with spirituality or religion, but is something still beyond our ability to detect and understand.
This tension between the immaterial (religious, spiritual) and the material does not seem likely to go away in the near term. We're stuck with it.
