In a landmark study published Monday in the journal Proceedings of the National Academy of Sciences, the first modern brain scans of people tripping on LSD illustrate the neural bases of the psychedelic drug's powerful consciousness-altering effects.
The research, which was conducted by the Beckley/Imperial Research Programme in the U.K., showed that LSD reduces connectivity within brain networks and boosts connectivity between brain networks that don't normally interact.
"Normally our brain consists of independent networks that perform separate specialized functions, such as vision, movement and hearing -- as well as more complex things like attention," Dr. Robin Carhart-Harris, a psychedelic researcher at Imperial College London and one of the study's authors, said in a statement. "However, under LSD, the separateness of these networks breaks down and instead you see a more integrated or unified brain."
Carhart-Harris and his colleagues scanned the brains of 20 healthy volunteers over the course of a six-hour LSD session after they'd been injected with a high dose of the drug. Two types of brain scans -- functional magnetic resonance imaging, or fMRI, and magnetoencephalography -- measured brain activity by detecting changes in blood flow and changes in electrical currents.
While their brains were being scanned, the participants performed a variety of cognitive tests. The brain scans of the volunteers on LSD were later compared to the brain scans of 20 volunteers who'd received a placebo.
The scans of the LSD recipients revealed a brain state "not entirely dissimilar" to psychosis, in which brain networks that are normally separate instead communicate with each other. In particular, the visual cortex communicated much more with other parts of the brain, explaining the vivid and often emotionally charged hallucinations experienced by many LSD users.
What does a more "unified" brain feel like? According to Carhart-Harris, it involves more fluid, flexible thinking, unusual associations and perceptions, vivid visions and perhaps enhanced creativity.
Our thinking in childhood starts out being more fluid and flexible, and tends to get more rigid and focused as we age, the researchers said. LSD, then, might help some users return to a childlike sense of wonder and imagination.
"You essentially have a state which is fundamentally plastic," Carhart-Harris told The Huffington Post. "You've turned up the heat on the system, like a solid you're starting to melt, and it's becoming more plastic, flexible and malleable."
The enhanced brain connectivity observed by the researchers also offers clues into the brain changes associated with "ego dissolution" -- the feeling of losing one's normal sense of self and reconnecting with oneself, others and the world in a deeper way.
Ego dissolution is a common experience for psychedelic users who take drugs like LSD and psilocybin in moderate to high doses. To help trippers navigate the experience of ego death, renowned American psychologist Dr. Timothy Leary, along with Ralph Metzner and Ram Dass, in 1964 published a guide for psychedelic journeyers modeled after the Tibetan Book of the Dead.
While neuroscientists have developed a strong understanding of how LSD acts on serotonin receptors in the brain, they've been less clear on how these chemical changes lead to profound shifts in consciousness like the ones described by Leary.
The Beckley/Imperial findings add heft to a growing body of research on the neurological effects and therapeutic benefits of psychedelics. While most of the existing research has been conducted on animals and more human trials are needed, studies have shown that LSD-assisted psychotherapy holds promise for treating depression, addiction and end-of-life anxiety.
More broadly, the new study offers a lens through which to better understand consciousness as a whole.
"Studying how psychedelic drugs such as LSD alter the ‘normal’ brain state is a way to study the biological phenomenon that is consciousness," Dr. David Nutt, a professor of neuropsychopharmacology at Imperial and the study's lead author, told Nature. "We ultimately would also like to see LSD deployed as a therapeutic tool."