How does your brain know something is real?
It’s a misty day in New York. Thanks to my computer screen, I think I see and hear that neuroscientist Nadine Dijkstra. But how can I be sure?
“We create as much our perception of reality as we perceive it,” she explains.
Rather than roughly asking her to perform a battery of tests to prove that she exists, I trust my eyes and my ears. It is an effective way to live. While neuroscientists could assert details, most agree that perception – essentially, how we process sensory information to create a coherent experience – implies the active construction of a reality, as opposed to the passive reception of the world around us.
For example, when you see a very popular road, you actively create this reality, combining information from your senses (sites and sounds of Whooshing) with past experiences (knowing that you have already traveled this popular boulevard). Quickly understand that cars accelerating on the street are real helps you protect yourself.
This reality model is effective, but not infallible: sometimes our brain is still wrong. This dissonance is something that Dijkstra, who works as a main instructor in Imagine Reality Lab at University College London, examines in his latest study, recently published in Neuron.
How a psychologist from the beginning of the 20th century deceived brains
A large part of Dijkstra’s work is inspired by revolutionary psychologist Mary Cheves West Greky. In a seminal article in 1910 on imagination and perception, subjects asked subjects to visualize objects – a red tomato, a green leaf, etc. – On an empty wall. Secretly, in this apparently empty space, the images barely visible projected barely visible from these same objects on the wall.
The subjects were not the wisest, attributing the objects perceived to their imagination instead of projections. He appeared, thought about Gary, that “the image of the imagination must have a lot in common with the perception of daily life”.
More than a century later, many researchers agree, believing that imagination and perception work together to create our sense of reality. But how does our brain know what is real and what is not? Dijkstra’s new research can have the answer.
Test brains in the 21st century
“We expected the results to be more complicated and nuanced,” said Dijkstra.
Instead, the brain activity measured by functional magnetic resonance imaging scans (IRMF) told Dijkstra a clear story: the level of activity in the fusiform gyrus could predict whether someone thought or not that an image was real. The region, located on both sides of the brain behind the temples, plays an important role in the recognition of faces and objects, but its ability to sort real fake is something that neuroscientists were not aware before.
The study was a modern touch of Gerky’s experience. Instead of projecting fruit and other objects on a wall, Dijkstra and his colleagues asked participants to imagine sets of diagonal lines on a screen. These lines were then projected into the irmf machine via a mirror. (The use of simple forms, like diagonal lines, has facilitated the forecast of what the subjects could visualize. Ask people to imagine a sheet, and they could imagine a plethora of shapes and colors.) The diagonal lines were displayed on a noisy background – think of static television – to make more difficult to distinguish the reality of the imagination.
When someone saw real projected lines, the activity in the fusiform gyrus was stronger than when he knew he simply imagined the diagonal lines. At the front of the brain, the anterior insula of the prefrontal cortex, which acts as a kind of hub between the brain networks, also showed increased activity when the participants saw the lines projected.
However, when someone confused the lines imagined for real, having essentially having a light hallucination, the regions of the fusiform gyrus and the anterior insula have lit – as if they had seen the real thing.
The “reality threshold” of the brain
These results led Dijkstra and his team to conclude that the imagined and perceived signals combine to create a “reality signal”. If it is strong enough, this signal crosses a “threshold of reality” and we accept what we perceive as an objective reality.
While she believes that activity at the Fusiform gyrus determines if something passes the reality threshold, Dijkstra said her research was in her early days. This could be “the opposite”, she notes, with an activity in the prefrontal cortex deciding “if something is real or not on the basis of another signal”, then to strengthen this “fusiform gyrus to stimulate your experience or make things more lively”.
Look beyond brain scanners
How the reality threshold has passed is important. Prove a causal link between activity in the fusiform gyrus and hallucinations, for example, could allow doctors to stimulate this part of the brain to treat the symptoms of schizophrenia and other brain disorders.
Not only can this research shed light on the reasons why humans see things that do not exist, but it can also explain why we sometimes do not believe our eyes. When she moved to London in the Netherlands for the first time, Dijkstra saw a creature in the distance by walking in her neighborhood. She assumed that he was a dog, even if he wandered alone. “I was really surprised. I said to myself: “Where is the owner? I really saw a dog. If she had turned away and had not questioned her reality, she might not have realized that what she saw was a fox, one of the 10,000 people who called her a new city. Dijkstra perceived something that did not correspond to his past experiences and, for a moment, saw something that did not exist.
As for the future of his research, there are so many unanswered questions about perception, explains Dijkstra, for example if people with lively imaginations are more likely to hallucinate. In this area, it is important to regularly challenge what you think real. “You can have this really cool idea that makes sense and it seems to explain so much, and then it turns out to be completely false,” she said. “And it’s okay, we are always making progress.”
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