Researchers say two-way communication is possible with people who are asleep and dreaming. Specifically, with people who are lucid (清醒的) dreaming — that is, dreaming while being aware you’re dreaming.

In separate experiments, scientists in the U.S., France, Germany and the Netherlands asked people simple questions while they slept. Sleepers would respond by moving their eyes or faces in a certain way to indicate their answers.

“Since the1980s, we’ve known that lucid dreamers can communicate out of dreams by using these signals,” says Karen Konkoly, a Ph.D. student at Northwestern University, who is the first author on the study published this month in Current Biology. “But we were wondering, can we also communicate in? Can we ask people questions that they could actually hear in their dreams so that we could kind of have a more meaningful conversation?”

Lucid dreaming is not common. So to study it, they found people who had experience with it and also trained people to try to make lucid dreaming more likely. Before they went to sleep, the participants were also trained on how to communicate their answers. Special sensors measured people’s eye movements or experts would judge their facial movements. For example, a typical question would be to ask what is 8 minus 6. A 19-year-old American man was able to respond by moving his eyes left-right, left-right-two times-to signal “2”.

Out of the 158 trials among 36 participants, about 18% of the time they were able to give correct answers. In another 18%, it wasn’t clear if participants were responding or not. They were wrong 3% of the time. Most often, 61%, participants didn’t respond at all.

The researchers write that their findings present “new opportunities for gaining real-time information about dreaming” and “could begin a new era of investigations into multiple dimensions of sleep”.

Konkoly says there’s the possibility of one day doing a sort of “dream therapy (疗法)” for talking down people experiencing lucid nightmares.

In the good old days, gold miners could seek out visible spots of bling at the surface in order to find deeper, richer veins. These days, prospectors must examine samples of dirt for more minute traces suggestive of a hidden mine below. Analysing water from boreholes can also provide clues, but boreholes are scarce and new ones are costly and time-consuming to drill.

Trees offer an alternative that has come off in Australia. The idea has been around since the 1940s but, until now, never practical. Some trees have roots that reach deep underground, drawing up water and, along with it, tiny quantities of minerals that end up distributed throughout the tree. In this way, even lofty leaves bear traces of what lies far beneath. In areas where there is no gold, leaves may have a background level of 0. 15 parts per billion (ppb) of gold; on gold-rich sites that can rise to 4ppb.

In proof-of-principle studies over the last few years, Nathan Reid and his team at CSIRO, Australia’s national science agency, have shown that biogeochemical prospecting closely agrees with the surface and groundwater analyses. Inspired by these results, Marmota, an exploration firm, put the method to the test at its Aurora Tank site, 50km from the highly-productive Challenger mine in South Australia.

Leaves collected immediately around a known deposit that lies beneath ten metres of rock contained traces of gold. Further samples were taken 40 metres apart around known deposits, and at wider spaces farther out. This turned up several anomalies, where gold seemed to be present but other tests had shown nothing. “The usual surface sample testing was saying ‘Don’t drill here’,” says Colin Rose, Marmota’s executive chairman, “but the tree sampling was saying ‘Drill here’. ” Then came the pay-off. Drilling revealed a five-metre-thick vein with 27g of gold per tonne, more than 30 metres below the surface. A metre-thick inner layer held an impressive 105g per tonne.

Marmota is keen to explore further. Prospecting with trees is starting to look less like a scientific curiosity and more like a golden opportunity.