Arnold-Forster and Saint-Denys’s work was mostly ignored, however, and during the following decades lucid dreams were over-looked for more “serious” lines of enquiry. But in recent years neuroscientists have recently started embarking on some equally eccentric experiments. Earlier this year, for instance, Jennifer Windt at the Johannes Gutenberg-University of Mainz in Germany decided to find out if lucid dreamers could tickle themselves in a dream. That might sound whimsical, but it helps to test the level of self-awareness in dreams. In real life, we can’t tickle ourselves because we know that what we’re doing, meaning that the brain damps down the sensations that would normally cause us to break down in giggles. Importantly, the same was true in lucid dreams; the subjects found it difficult to make themselves laugh, which suggests their dream self has a high degree of awareness of their bodily actions and sensations, and minimises the response.

Interestingly, Windt also asked the subjects to ask other characters in the dream to tickle them. “Several times, dream characters just refused,” says Windt. “They behaved as if they had a mind and intentions of their own.” When the other being did tickle the dreamer, however, the effect was often underwhelming – which suggests the brain still recognised its control over those other dream characters.

Sleep-walking

Studying the passage of time in dreams had proven trickier to study, however, until Daniel Erlacher at the University of Bern in Switzerland set up an ingenious experiment.

It began when he was investigating the way the brain imagines different actions; when we dream of running, do we activate the same regions that are busy during a race, for instance? His early experiments suggested yes, but somehow they seemed to be strangely drawn out.

So, inviting some skilled lucid dreamers to his specially equipped sleep lab, he asked his subjects to perform various kinds of tasks during their dreams: once they had gained lucidity, they had to walk 10 paces, count to 30 or perform an elaborate gymnastics routine, for instance. To time the duration of their actions, he used a peculiar aspect of the dreaming mind: although the body is paralysed, eye movements tend to be translated to the body. In this way, the subjects could signal the start and end of the actions by rolling their eyes left and right a couple of times. Along the way, Erlacher measured their brain activity and muscle movements, to be sure they weren’t just pretending to be asleep.

As he expected, the dreamers sometimes took up to 50% longer to complete the routines than you would in real life, suggesting that they were somehow playing out their tasks in slow motion, even though they didn’t realise it at the time. “They reported that it felt exactly the same as in wakefulness,” says Erlacher.