Many researchers have been interested in the idea that psychedelics facilitate communication across the brain and, more specifically, how the default-mode network in the brain, arguably science's best biological correlate of the self, normally works to constrain this.
"Psychedelics" are substances with the ability to expand human awareness beyond our normal modes of perception. Some may be the most amazing substances known to humanity, so potent that just 1/10,000th of a gram can send one on a journey beyond time and space, beyond life and death.
Carhart-Harris performed the UK's first clinical trial of psilocybin -- the active ingredient in magic mushrooms -- for treatment-resistant depression. It was a small trial with no control group, but the results gave cause for optimism, with 5 of the 12 participants no longer clinically depressed three months after the treatment.
In other psilocybin research, one dose was found to help people with life-threatening cancer face death. Ayahuasca, a hallucinogenic concoction drunk for centuries as part of religious rituals in South America, has also been found to improve hard-to-treat depression. It contains the psychedelic compound dimethyltryptamine (DMT).
The vine is usually mixed with leaves containing the psychedelic compound DMT (diemethyltryptamine). It causes hallucinogenic experiences, and is made up of a chemical compound that already occurs within the human body endogenously (as well as in a number of plants). This means our brains are naturally set up to process the compound because it has receptors that exist specifically to do so.
While research into psychedelics is still thin on the ground, a meta-analysis of six studies carried out between 1966 and 1970 concluded that LSD was as effective as the standard treatment for alcoholism.
The Journal of Nervous and Mental Disease published results from the first study of LSD’s therapeutic potential in humans to appear in more than four decades. The controlled, double-blind study, which was conducted in Switzerland under the direction of Swiss psychiatrist Peter Gasser, measured the impact of LSD-assisted psychotherapy on 12 people with life-threatening diseases (mainly terminal cancer). “The study was a success in the sense that we did not have any noteworthy adverse effects,” Gasser says. “All participants reported a personal benefit from the treatment, and the effects were stable over time.”
LSD reduces connectivity within brain networks, or the extent to which nerve cells or neurons within a network fire in synchrony. LSD also seems to reduce the extent to which separate brain networks remain distinct in their patterns or synchronization of firing. Overall, LSD interferes with the patterns of activation in the different brain networks that underlie human thought and behavior.
And Ibogaine -- derived from the iboga plant -- has been used to treat heroin addiction. MDMA, or ecstasy, was found to help people who have experienced trauma.
Psychedelic drugs are not physiologically addictive and they are not necessarily that pleasurable either. "People often say, as our patients did, that this isn't a moreish drug. It's certainly not a hedonic drug," says Carhart-Harris. "Some even challenge whether it's a drug of recreation; maybe it's a drug of exploration." People taking such substances can have intense and disturbing experiences -- aka a bad trip.
Mind & Brain
There are a wealth of ideas about what goes on in the mind after someone takes a psychedelic substance. One is that the ego -- your sense of yourself as a separate entity -- dissolves, as the brain's "default mode network" goes offline, and brain areas that do not normally communicate with each other start working together.
Such drugs may also make our minds more malleable and open to new ways of thinking about the world and ourselves, which could help to break the negative patterns often associated with depression. Psilocybin may even offer a window into the consciousness of babies.
Brain scanning technology has allowed objective neuroscience to start catching up with the subjective experiences brought on by psychedelics. Scans have helped us discover that people who under the influence of psychedelic drugs show more diversity in their patterns of brain activity than people who had not taken the drug.
Recent work may have found out how LSD creates its long-lasting trippy effect. And brain scans of frequent ayahuasca users suggest that the visions it induces appear to be as real as anything the eyes actually see. Yet a psilocybin trip may be similar to a dream -- they look similar in an fMRI brain scanner.
Many creators of psychedelic drugs famously tested their products on themselves first. Alexander Shulgin, considered the world's foremost "psychonaut" is among those featured in our gallery of self-experimenters.
Some people hope to derive benefits from psychedelics without the tripping, by taking a low dose daily. Proponents say it improves their work-life and mood. Janet Lai Chang, a digital marketer in San Francisco, who took microdoses of LSD with her breakfast to help her deal with social anxiety. And one of our journalists took part in a trial of MDMA, which included getting his brain scannedÂ after taking the drug. It was quite an eye-opener.
In 2009, David Nutt was dismissed as chairman of the UK government's Advisory Council on the Misuse of Drugs. A week after his dismissal he wrote an editorial for New Scientist, urging the UK government to "take careful note of the evidence and develop a rational drug policy". He lamented that "Some politicians find it easier to ignore the evidence, and pander to public prejudice instead." Nutt's editorial provoked a big reaction from our readers.
In the UK today, the many obstacles to psychedelics research prevent scientists from uncovering medical benefits that could destabilise the UK government's tough stance on drugs, according to Ian Dunt, editor of Politics.co.uk.
While psychedelic medicine is experiencing a nascent renaissance, particularly in the US, the ascension of US President Donald Trump has sparked worries of a renewed so-called "war on drugs".
Despite this, the renewed interest in psychedelics science, and the necessarily painstaking nature of today's researchers, make it unlikely that this genie will be squashed back into its lamp any time soon.