The new findings raise questions about whether variations or alterations in this system could lead to hallucinations, invasive thoughts or even dreaming. But if an imagined signal is strong enough to cross the threshold, the brain takes it for reality.Īlthough the brain is very competent at assessing the images in our minds, it appears that “this kind of reality checking is a serious struggle,” said Lars Muckli, a professor of visual and cognitive neurosciences at the University of Glasgow. Such a system works well most of the time because imagined signals are typically weak. A study she led, recently published in Nature Communications, provides an intriguing answer: The brain evaluates the images it is processing against a “reality threshold.” If the signal passes the threshold, the brain thinks it’s real if it doesn’t, the brain thinks it’s imagined. So “why are we not constantly hallucinating?” asked Nadine Dijkstra, a postdoctoral fellow at University College London. The knowledge that unicorns are mythical barely plays into that: A simple imaginary white horse would seem just as unreal. The street would seem real and the unicorn would not. “I can look outside my window right now, and if I want to, I can imagine a unicorn walking down the street,” said Thomas Naselaris, an associate professor at the University of Minnesota.
Yet for most of us, the subjective experiences they produce are very different. Brain scan studies have repeatedly found that seeing something and imagining it evoke highly similar patterns of neural activity. Those aren’t just lyrics from the Queen song “Bohemian Rhapsody.” They’re also the questions that the brain must constantly answer while processing streams of visual signals from the eyes and purely mental pictures bubbling out of the imagination.
Is this the real life? Is this just fantasy?
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