The search for consciousness is one of the hardest problems in both philosophy and neuroscience.
We seem to know that we are conscious beings. We have an awareness of ourselves and our experiences. But, when we're asleep — or under anesthesia — that feeling disappears for long stretches of time. So is consciousness real? Is it just an illusion? Are animals conscious, too? What about babies?
For a long time, these questions were largely the domain of philosophy, but science has been slowly encroaching into this territory and coming up with some interesting findings.
In many ways, the work is just getting started. These explorations might someday lead to a full understanding of how consciousness arises — or it might not.
But the discoveries so far are tantalizing, including that people in vegetative states and animals might have more consciousness than previously thought and that people under anesthesia have particular brainwave patterns that seem to disrupt their ability to think.
Here are three recent ways that scientists have been trying to get a better handle on consciousness:
1) Studying the mirror self-recognition test
The mirror self-recognition test is technically a test of self-awareness, not of consciousness per se. But it has had a major influence on getting scientists to rethink their assumptions about animals' mental capabilities, including consciousness.
Basically the test works like this: Researchers put a mark on a test subject's face without them noticing (for example, under anesthesia). Then they bring that subject near a mirror. If the subject reaches up to touch the strange mark on his or her own face (rather than touching the mirror), it's assumed that the subject recognizes that the image in the mirror is "me" and therefore has a concept of "me."
In 1970, psychologist Gordon Gallup Jr published a paper in the journal Science showing that chimps could pass the mirror test, but that monkeys couldn't. (Cats and dogs also fail the test, although researcher Marc Bekoff has recently proposed a sniffing test for dogs, because they often rely more on smell than on vision.)
Next, developmental psychologists showed that human children acquired the ability to pass the mirror test between 18 and 24 months of age — at about the same time that they develop self-awareness. Or, at least they do in westernized cultures. (Maggie Koerth-Baker has an interesting piece in Scientific American on how the test might need to be modified for other cultures.)
Since then, other apes have also passed the test, including orangutans and gorillas. Some elephants and some magpies have passed. And in 2011, bottlenose dolphins possibly passed, depending how you interpret their behavior. (They don't have the hands to wipe off marks, but they do wriggle around to presumably get a good look at them.)
Researchers still disagree about whether passing the test really means that someone (or some animal) is having the conscious experience of self-awareness. For those who believe that this is the case, it could have an impact on animal-rights' issues, especially if an animal has the ability to consciously think about its own pain or captivity.
2) Studying vegetative states and the minimally conscious
Consciousness isn't a binary — on or off. There's a range of levels of awareness. For example, being awake is different from being asleep, which is different from being under anesthesia, which is different from being in a vegetative state, which is different from being in a coma.
Using sophisticated brain-imaging technology, researchers have started to realize that many patients classified as being in a vegetative state may actually possess more consciousness than it seems on the surface. What's more, being wrongly diagnosed could be affecting their chances of recovery.
One key study published in The Lancet in August of 2014 found that one-third of patients who had been diagnosed as unresponsive probably had some level of consciousness, according to a PET scan of brain activity. And PET scanning was able to predict with 74 percent accuracy how much function people had recovered at the end of a year.
They also studied the same people with a different technique — scanning with fMRI while asking the patient to imagine navigating through a house or playing tennis, which each activate different brain regions. This fMRI technique ended up guessing recovery with 56 percent accuracy.
Researchers have also been trying to produce similar results with the less expensive and less invasive EEG technique, which uses a more simple cap of electrodes, not a giant, costly machine.
And in previous work, researchers have been able to communicate with at least one patient in a vegetative state using the same imagination trick. (Imagine tennis for "yes" and navigating for "no.") This patient, known as patient 23, was able to correctly answer several simple yes or no questions about his life.
3) Studying people under anesthesia
Anesthesia is one of the odder experiences available to humankind. One moment you're there, the next you're totally gone. And the next thing you know, the operation's all over. It seems like a temporary coma, although researchers still don't have much of an idea of how it works. But they're beginning to use various types of technology to probe the brain and learn more.
Several studies have pointed to the neocortex and thalamus regions of the brain as key drivers of changes in consciousness. Some have found this by monitoring the brains of people under anesthesia.
In 2012, a study led by Patrick Purdon, of Harvard Medical School, used electrodes on the heads of volunteers to analyze their brainwaves as they became unconscious from the anesthetic propofol. They ended up picking up a big, slow oscillation of electrical activity that started right when they lost consciousness. The researchers suggest that these oscillations are making the brain's information processing less efficient.
Interestingly, the oscillation isn't synchronized across the brain, which suggests that different areas of the brain are having difficulty communicating with each other. (This research was also featured on the Black Box episode of Radiolab, if you want to hear more.)
It hasn't yet been demonstrated whether these oscillations cause the loss of consciousness or are just a symptom of it.