I was amused by Conal Urquhart's description in the Observer of the novelist Lionel Shriver being sucked into an MRI brain scanner "that resembles a giant washing machine". I see her tumbling around with the rest of the laundry, including actor Keith Allen and former MP Evan Harris, to emerge bright and uplifted.

The three of them were participants in a brain imaging study into the effects of MDMA ("ecstasy") on brain function, parts of which will be televised on Channel 4's Drugs Live documentary on Wednesday and Thursday night.

Harris, who is also a doctor, said the trial could "pave the way to further research into potential therapeutic uses of MDMA, such as in the treatment of PTSD [post-traumatic stress disorder]". But others have raised doubts. Urquhart quoted a Home Office spokesman as saying that "televising the use of illegal drugs risks trivialising a serious issue".

Surely, though, developing improved treatments for severe health problems is also a serious issue?

Readers may remember my article earlier this year about a similar brain-imaging study on psilocybin, the active ingredient in magic mushrooms. The research formed part of the Beckley Foundation/Imperial College Psychopharmacological Research Programme, a collaboration between the Beckley Foundation, which I founded and direct, and Professor David Nutt's group at Imperial College. The MDMA study featured in Channel 4's Drugs Live is a continuation of that programme.

Contrary to expectations, psilocybin decreased cerebral blood flow, particularly to brain regions that act as "connector hubs" responsible for filtering and co-ordinating the flow of information through the brain. These hubs impose a top-down control on our awareness, integrating sensory inputs and prior expectations into a coherent, organised and censored experience of the world. By reducing blood supply to the hubs, and thereby decreasing their activity, psilocybin allows a freer, less constrained state of awareness to emerge.

This finding provides a neuroscientific underpinning for the metaphor of the brain as a "reducing valve" whose censoring activity is turned down by psychedelics – an idea popularised by the novelist Aldous Huxley in his 1954 essay The Doors of Perception.

Besides providing insights into consciousness and brain function, the results from our psilocybin studies highlight important new therapeutic possibilities. One of the hubs throttled back by psilocybin is known to be chronically overactive in depression. By lowering the activity of this region, psilocybin may allow the unremitting ruminative thought patterns that underlie depression to be reset. On the back of this finding, the Medical Research Council has awarded a major grant for a study of psilocybin in the treatment of severely depressed patients, which has just begun.

Psilocybin reduces the blood supply and activity of another "connector hub", which is overactive in cluster headaches. Cluster, nicknamed the "suicide headache" because it is so agonising, is notoriously difficult to treat – though anecdotal evidence suggests that psilocybin and LSD provide relief. Unfortunately, patients currently have to obtain these substances illegally, without the benefit of medical advice and supervision.

As these results prove, brain imaging research can add invaluable insights to knowledge gained from other scientific and clinical fields. The new MDMA research aims to do just that.

Growing out of the Beckley/Imperial psilocybin research, the MDMA work also uses fMRI to monitor activity in different parts of the brain, and compares the effects of the drug with those of an inactive placebo.

MDMA is a pure form of the club drug ecstasy, which is often contaminated with other substances. The drug used in these studies is held legally under a Home Office licence (so Channel 4 is not "televising the use of illegal drugs"). The MDMA is administered at a controlled dose, with informed consent, using procedures for which we have gained ethical approval.

Our brain imaging research complements work in progress in America into the efficacy of MDMA-assisted psychotherapy as a treatment for PTSD: the participants include war veterans, police officers and firefighters. The research is urgent because Pentagon statistics released in June show suicides among active troops running at about one per day, significantly outnumbering combat deaths.

Our imaging study is still incomplete, but preliminary results provide fascinating insights. After taking MDMA, positive memories were experienced as more vivid than after placebo. Correlating with this subjective experience, MDMA evoked an increased activation of the visual cortex compared with placebo. By contrast, during recollection of negative memories, the brain scans showed a decreased activation under MDMA compared with placebo.

Our finding suggests that MDMA may enable PTSD patients to access negative memories without a feeling of overwhelming threat, which could enable subjects to better confront and wash out their traumatic experiences.

The scans have also shown that MDMA reduces the connectivity – that is, the degree of synchronisation – between two important "connector hubs" in the brain that show elevated connectivity in depression. The finding suggests that, like psilocybin, MDMA could be valuable in the treatment of depression, by breaking over-rigid, introspective thinking patterns.

Securing funding for research of this kind is not easy. Using MDMA and other controlled drugs for scientific purposes is legal, so long as the appropriate licences are granted and complied with. However, the prohibitionist policies towards psychoactive substances create a strong taboo, which makes many scientists, universities and funding bodies unwilling to become involved.

Evan Harris is surely right that research into potentially valuable treatments for serious and intractable conditions should be encouraged. While a small charity like the Beckley Foundation does the best it can to initiate, support and collaborate in scientific research, we need to raise awareness in order to attract further funding.

Debate should be fostered, not stifled, so I see the involvement of Channel 4 as serving an important educational purpose. We would have no problem with a documentary investigating how a substance such as pethidine – a Class A drug like MDMA – alleviates obstetric pain. Why treat MDMA differently?

The illegal status of many psychoactives is a key policy challenge of our time, and seriously interferes with scientific research. Let us hope that before too long, the stain of the taboo will be washed away, and scientific evidence will prevail.

Amanda Feilding is director of the Beckley Foundation, a thinktank working for health-oriented drug policies based on scientific research