WHAT is consciousness? This is arguably the biggest remaining mystery of the human brain. No wonder it is known as 鈥渢he hard problem鈥�. We can鈥檛 even agree whether consciousness is one thing or a variety of different states. However, new ways of exploring that question shed some intriguing light on this most elusive of concepts.
Though we use language like 鈥渓osing consciousness鈥� for fainting or falling asleep, researchers have long understood that consciousness is more complicated than just flipping a metaphorical switch from 鈥渙n鈥� to 鈥渙ff鈥�. However, there is still much debate over whether it is a single phenomenon with many continuous shades, which you might picture as a dimmer switch, or a collection of discrete states, like separate television channels.
Thinking about consciousness from the perspective of a physicist may help resolve the question. That鈥檚 because the brain constantly shifts between states defined by patterns of electrical signals, and physicists have metrics for examining such busy, ever-changing systems. In 2014, at the University of California, San Francisco, and his colleagues .
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Entropy describes how disordered a system is. One measure of entropy is how many different microscopic configurations (such as arrangements of water molecules in a glass) there are in a given macroscopic property (such as the volume of that glass). The researchers proposed that brain states with greater entropy, as measured by the variety and number of electrical signals and connections between different parts of the brain, are richer in information. This suggests there is a spectrum of consciousness with some minimum level of brain entropy necessary for any consciousness at all.
Calculating entropy in the brain
Some facets of this hypothesis have been tested by calculating the brain鈥檚 entropy from brain scans. For instance, several studies show that consuming psychedelics can increase the brain鈥檚 entropy. Others reveal that people鈥檚 brains have less entropy during deep sleep than they do while awake.
at Pompeu Fabra University in Spain and his colleagues have used another idea from physics, equilibrium, to explore consciousness. A physical system is in equilibrium when in its most stable state. The researchers wanted to know how close to equilibrium the electrical states of the brain were while people performed different tasks. Using a devised by Albert Einstein along with information from neuroimaging, they found that the . Again, the equilibrium approach seems to suggest that there are many shades of consciousness.
Multidimensional states
Perhaps unsurprisingly, not everyone agrees. 鈥淭he idea that there is a single scale for measuring consciousness, the dimmer switch idea, is oversimplified,鈥� says at Trinity College in Connecticut. He argues that conscious states are more likely to correspond to a multidimensional scale because consciousness is fundamentally related to subjective experience, and an individual鈥檚 experience has so many different facets depending on their senses and environment. He gives the example of psychedelic drugs. 鈥淧sychedelics are going to change your sentience, but it鈥檚 not like, now I鈥檓 more conscious or less conscious than I was before, I鈥檓 differently conscious.鈥� The increased entropy of the brain on psychedelics captures something of that difference, but we don鈥檛 yet have a good enough theory of consciousness to qualify it further, he says.
at the Italian Institute of Technology points out that even scientists from different fields have different notions of what consciousness is. 鈥淗ow can one find an appropriate quantifier for some fuzzily defined concept?鈥� he says.
Deco admits that none of his experiments have fully tested the dimmer switch idea because they are designed to observe one state at a time to make the results unambiguous. How the brain transitions between states isn鈥檛 clear. Nevertheless, he believes that approaches inspired by concepts in physics like equilibrium and entropy have the potential to quantify such properties of consciousness and will be crucial for determining whether it is a continuum or a collection of separate channels.
