Six years ago, Inception wowed everyone with the idea of implanting memories and dreams into the human mind. Now scientists are working to do something very similar IRL.
Unlike the fictional enterprise run by Leonardo di Caprio, this isn't a long con - experts think it could eventually lead to better treatments for depression, autism, and a variety of other brain-related conditions.
The experiments are based around the idea of neurofeedback, where the brain is constantly monitored via fMRI machines and the results can be seen in real-time, but with the extra ability to influence the brain's activity patterns in addition to just watching them.
Using this technique, a team led by scientists from Brown University were able to get people to think of the colour red while they were actually looking at black and white stripes - and the participants weren't even aware that they'd been influenced to see a colour that wasn't there.
The researchers managed this by training 18 volunteers to associate particular colours with particular patterns. The research targeted two specific areas of the brain, known as V1 and V2, which are the parts of the brain's cerebral cortex that process basic visual information from the eyes.
"This is the first clear study that shows that V1 and V2 are capable of creating associative learning," said one of the team, Takeo Watanabe.
First, Watanabe and his team measured the participants' reactions to various combinations of red, green, and grey, and horizontal and vertical stripe patterns. Twelve of the 18 people were then shown a circle with grey vertical stripes inside it, and asked to visualise ways of making it bigger.
What the volunteers didn't know, though, was that the circle actually got larger whenever their brain activity showed they were thinking about the colour red. This was enough to create a link between vertical stripes and brain activity related to red, even though the stripes were actually grey.
The 'trained group' also showed a slight association with horizontal stripes and green - the other colour besides grey used in the research - so when the 'red' pattern wasn't shown, participants assumed it must be 'green' instead.
The participants weren't actually told anything about colours during the final test. Instead, their brains were being subliminally taught to associate 'red' brain activity with achievement and reward.
Nor were they actually 'seeing' or hallucinating the colour red when it wasn't there - the experience is more akin to synaesthesia, says Watanabe, where certain associated thoughts involuntarily come to mind. Amazingly, evidence of the same association could still be seen up to five months later.
The researchers now want to see if this kind of brain training can be used for educational or therapeutic purposes. It's possible that people might be able to absorb information without even realising it.
"Our brain functions are mostly based on associative processing, so association is extremely important," said Watanabe. "Now we know that this technology can be applied to induce associative learning."
The findings are published in Current Biology.