Deceiving the brain: scientists have discovered how optical illusions control our minds

Optical illusions play on the brain's biases, making it perceive images differently than they really are. Scientists conducted a study on mice to understand how the brain processes visual information.

The study focused on the illusion of neon color spreading, which includes patterns of thin lines on a solid background. This is reported by the LiveScience website with reference to a study published on ScienceDirect.

Scientists conducted an experiment, observing how the brain of mice reacts to the optical illusion. Parts of the lines in the picture have a different color - lime green - and the brain perceives these lines as part of a continuous shape with a clear boundary - in this case, a circle. The closed shape also looks brighter than the lines surrounding it.

Previously, scientists have found that this illusion causes the human brain to falsely fill in and perceive fictional contours and brightness, but there has been debate about how the brain reacts in a particular moment. Now, scientists have demonstrated that the illusion works in mice for the first time. This allowed them to look into the rodents' brains and see what was going on.

In particular, they enlarged a part of the brain called the visual cortex. When light hits the eyes, electrical signals are sent through nerves to the visual cortex. This area processes visual data and sends it to other areas of the brain, allowing us to perceive the world around us.

The visual cortex consists of six layers of neurons, which are sequentially numbered V1, V2, V3, and so on. Each layer is responsible for processing different characteristics of the images that strike the eye, with V1 neurons processing the first and most basic level of data, while the other layers are referred to as "higher visual areas." These neurons are responsible for more complex visual processing than V1 neurons.

Until now, scientists have discussed to what extent V1 neurons respond to the illusory brightness that people perceive when looking at the illusion of a spreading neon color. In a series of laboratory experiments on mice, the researchers showed that these neurons play a fundamental role in this process, and that their activity is also constrained by feedback from V2 neurons. Thus, there is a back and forth movement between these different layers of the visual cortex.

"This knowledge could strengthen our understanding of consciousness," the researchers commented in the article, which was published in the journal Nature Communications.

"The observed connections between V1 and V2 during illusion processing indicate that consciousness is a top-down process, as opposed to a bottom-up process," co-author Masataka Watanabe, an associate professor of systems innovation at the University, explains.

"Top-down information processing explains how our brains interpret what we see, taking into account previous experience, rather than relying solely on visual stimuli. Bottom-up processing works in the opposite way: different characteristics of an image are connected together like puzzle pieces, forming a complete picture without input from human memory.

"There have been studies before that suggested that consciousness is a top-down information processing process, but this mouse study provides direct evidence for this," Masataka said. However, the answer is not black and white as some scientists argue that consciousness likely results from a mixture of both.

What is the new evidence? During the study, mice were shown a combination of illusions propagated by neon color and other similar-looking patterns that did not cause the illusion. At the same time, Watanabe and his colleagues measured neuronal activity in the rodents' brains using implanted electrodes. The team also measured whether the mice saw the illusions as vivid by assessing how dilated or constricted the pupils in their eyes were. This response was consistent with that observed in humans when we perceive changes in light levels.

"V1 neurons respond to both illusory and non-illusory images, but they take longer to respond to the former. This supports the theory that V1 neurons need feedback from higher visual areas to process these types of illusions," the team said.

The researchers then tried to experimentally inhibit the activity of higher visual area neurons, finding that V1 neurons were less likely to respond to illusions. This provided further evidence that a higher-level feedback loop is required to perceive an illusion.

According to Watanabe, the team plans to conduct further studies in which they will examine the activity of neurons in the higher visual area in mice. They hope that this will shed more light on the neural mechanisms underlying the consciousness of mice and, accordingly, humans.

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