Neuroscientists observed a sustained increase in neural signal diversity – a measure of the complexity of brain activity – of people under the influence of psychedelic drugs, compared with when they were in a normal waking state. The diversity of brain signals provides a mathematical index of the level of consciousness. For example, people who are awake have been shown to have more diverse neural activity using this scale than those who are asleep. This, however, is the first study to show brain-signal diversity that is higher than baseline, that is higher than in someone who is simply 'awake and aware'. Previous studies have tended to focus on lowered states of consciousness, such as sleep, anaesthesia, or the so-called 'vegetative' state. The team say that more research is needed using more sophisticated and varied models to confirm the results but they are cautiously excited.
Professor Anil Seth, Co-Director of the Sackler Centre for Consciousness Science at the University of Sussex, said: "This finding shows that the brain-on-psychedelics behaves very differently from normal. "During the psychedelic state, the electrical activity of the brain is less predictable and less 'integrated' than during normal conscious wakefulness – as measured by 'global signal diversity'. "Since this measure has already shown its value as a measure of 'conscious level', we can say that the psychedelic state appears as a higher 'level' of consciousness than normal – but only with respect to this specific mathematical measure." For the study, Michael Schartner, Adam Barrett and Professor Seth of the Sackler Centre reanalysed data that had previously been collected by Imperial College London and the University of Cardiff in which healthy volunteers were given one of three drugs known to induce a psychedelic state: psilocybin, ketamine and LSD. Using brain imaging technology, they measured the tiny magnetic fields produced in the brain and found that, across all three drugs, this measure of conscious level – the neural signal diversity – was reliably higher.