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Thought according to Descartes is the mind's defining feature. The thought is proof of the existence of reality, or at least the reality of one's own mind. But what would become of that reality if we could implant thoughts into people's minds?

A group of scientists in Canada and France report that they tricked a group of volunteers into thinking they had done just that—suggesting, using little more than stage magic, that such a feat may one day really be possible. In a study to be published next month in the journal Consciousness and Cognition, researchers report that by using a kind of magic called mentalism they were able to artificially "implant" the experience of thought in the minds of volunteers.

The researchers told 23 undergraduate psychology majors that they were taking part in a study to see if an fMRI brain scanner could accurately read thoughts and influence their mind. The scanner, though, was actually a non-working prop.

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In order to convince participants that the scanner could read minds, the researchers asked them to silently think of a two-digit number and then name it aloud after being scanned. When the volunteers revealed the number chosen, the researchers stealthily wrote it on the blank paper produced by the scanner, duping the volunteers into thinking that the machine read minds.

In the second phase of the experiment, the volunteers were told that the machine had been programmed to put a number into their minds. The volunteers were scanned again and asked to reveal the number they had silently been thinking. The researchers again stealthily wrote the number down and handed the paper over to show the volunteers that the scanner had been broadcasting that number at them.

Afterward, participants reported that they felt as though the machine had influenced their thinking, even though it of course had not. One reported that a number had just “popped” into their head; another said that there was  “a voice … dragging me from the number that already exists in my mind."

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While this isn't exactly thought-implantation in the vein of Inception,  it does demonstrate the immense power of suggestion alone to influence someone's thoughts. In this, it suggests that we are capable of believing we have thought thoughts that are not actually our own. When people are unaware of what influences their own choices, it leaves room for such deception to play a major role.

"We can make the vast majority of people believe something," lead author Jay Olson, a psychologist at McGill University, told me. "Aside from hypnosis, this is closest we have gotten to actually putting a thought in a person's mind."

Olson isn't suggesting that we are on the brink of mind control—that future, if possible at all, is very far off. To get there, he said, we would need to understand the specific neural patterns of individual thoughts and then stimulate that brain with that same pattern in a way that would likely be extremely invasive. Given that we are far from understanding many of the mere basics of brain human functionality, it's unlikely that researchers will be compromising Cartesian reality anytime soon.

But scientists have already performed a very similar trick in mice. By tagging mouse brain cells associated with a specific memory, they were able to engineer those cells to create a new memory of something that had never happened.

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In The Demon-Haunted World, Carl Sagan argues that implanting false memories in people isn't actually all that difficult if you're working with a gullible subject. He cites examples of therapists and hypnotists who convince their subjects that they've been abducted by UFOs or abused as a child.

"False memories can be implanted even in minds that do not consider themselves vulnerable and uncritical," he wrote.

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But Olson points out that part of the significance of his study is that his audience wasn't gullible—they were a bunch of skeptical psychology undergrads.

"There is so much deception being used here," he said. "But once they saw that the machine was correctly guessing their number they drew the most reasonable conclusion possible from what we told them."

Olson and company's end goal wasn't to actually implant a thought in someone's mind but to understand more about how agency in the thought process works. By merely suggesting that the machine had implanted a thought in their brain, they were able to successfully convince volunteers that they had no choice in their number. For now, this research mainly highlights the disconnect between our brains and our bodies—how easy it is for us to not realize that we have control when in fact we really do. They hope that by studying this aspect of psychology, they might obtain insight into certain mental conditions such as schizophrenia.

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But how many leaps, really, they wonder, are there between convincing someone they do not have control of their own thoughts and actually controlling them?

"If people believe it can influence thoughts, would they also believe – and experience – ostensibly implanted feelings or judgements?" the researchers ask. "Does simulated thought insertion reduce people’s belief in free will?"