Ella Cohen
How do a few pounds of gray goo in our skulls create our conscious experience—the blue of the sky, the tweet of the birds? Few questions are so profound and important—or so hard. We are still very far from an answer. But we are learning more about what scientists call "the neural correlates of consciousness," the brain states that accompany particular kinds of conscious experience.
Most of these studies look at the sort of conscious experiences that people have in standard FMRI brain-scan experiments or that academics like me have all day long: bored woolgathering and daydreaming punctuated by desperate bursts of focused thinking and problem-solving. We've learned quite a lot about the neural correlates of these kinds of consciousness.
But some surprising new studies have looked for the correlates of more exotic kinds of consciousness. Psychedelic drugs such as LSD were designed to be used in scientific research and, potentially at least, as therapy for mental illness. But of course, those drugs long ago escaped from the lab into the streets. They disappeared from science as a result. Recently, though, scientific research on hallucinogens has been making a comeback.
Robin Carhart-Harris at Imperial College London and his colleagues review their work on psychedelic neuroscience in a new paper in the journal Frontiers in Neuroscience. Like other neuroscientists, they put people in FMRI brain scanners. But these scientists gave psilocybin—the active ingredient in consciousness-altering "magic mushrooms"—to volunteers with experience with psychedelic drugs. Others got a placebo. The scientists measured both groups' brain activity.
Normally, when we introspect, daydream or reflect, a group of brain areas called the "default mode network" is particularly active. These areas also seem to be connected to our sense of self. Another brain-area group is active when we consciously pay attention or work through a problem. In both rumination and attention, parts of the frontal cortex are particularly involved, and there is a lot of communication and coordination between those areas and other parts of the brain.
Some philosophers and neuroscientists have argued that consciousness itself is the result of this kind of coordinated brain activity. They think consciousness is deeply connected to our sense of the self and our capacities for reflection and control, though we might have other fleeting or faint kinds of awareness.
But what about psychedelic consciousness? Far from faint or fleeting, psychedelic experiences are more intense, vivid and expansive than everyday ones. So you might expect to see that the usual neural correlates of consciousness would be especially active when you take psilocybin. That's just what the scientists predicted. But consistently, over many experiments, they found the opposite. On psilocybin, the default mode network and frontal control systems were actually much less active than normal, and there was much less coordination between different brain areas. In fact, "shroom" consciousness looked neurologically like the inverse of introspective, reflective, attentive consciousness.
The researchers also got people to report on the quality of their psychedelic experiences. The more intense the experiences were and particularly, the more that people reported that they had lost the sense of a boundary between themselves and the world, the more they showed the distinctive pattern of deactivation.
Dr. Carhart-Harris and colleagues suggest the common theory that links consciousness and control is wrong. Instead, much of the brain activity accompanying workaday consciousness may be devoted to channeling, focusing and even shutting down experience and information, rather than creating them. The Carhart-Harris team points to other uncontrolled but vivid kinds of consciousness such as dreams, mystical experiences, early stages of psychosis and perhaps even infant consciousness as parallels to hallucinogenic drug experience.
To paraphrase Hamlet, it turns out that there are more, and stranger, kinds of consciousness than are dreamt of in our philosophy.