A groundbreaking study published in Neuron on June 5 reveals how the brain tells the difference between real and imagined images — a cognitive skill most of us take for granted but one that breaks down in disorders like schizophrenia. The research identifies two specific brain regions that appear to work together to separate visual reality from mental imagery.
“Being able to keep apart your inner world and actual reality is quite useful for normal functioning in daily life,” said Nadine Dijkstra, co-author and cognitive neuroscientist at University College London. “This is something that does go wrong in psychosis and schizophrenia,” she added.
The study, which adds fresh insight to a question long debated by philosophers, was praised for bridging the gap between neuroscience and the elusive concept of imagination. Thomas Naselaris, a neuroscientist at the University of Minnesota Twin Cities who was not involved in the study, called it “an important early step in disentangling perception and imagination.”
Blurring the Lines Between Seeing and Believing
To investigate how the brain distinguishes real visuals from imagined ones, Dijkstra and her colleagues asked volunteers to view simple images of black and white stripes over a noisy, static-like background. In some trials, participants were instructed to imagine the stripes while viewing the image and to report whether they genuinely saw the stripes and how vivid they appeared.
The results showed that when participants perceived the imagined stripes as more vivid, they were more likely to report them as real — even when the stripes were not actually present. This finding suggests that the vividness of a mental image plays a significant role in how we judge whether something is real.
Tracking the Brain’s “Reality Signal”
Using functional magnetic resonance imaging (fMRI), the researchers measured changes in brain activity as participants engaged in the task. They found that activity in the fusiform gyrus — a brain region known for processing high-level visual information — closely tracked the vividness of the stripes, whether they were real or imagined.
“The fusiform gyrus is tracking this ‘reality signal,’ this vividness signal that then predicts reality judgments,” Dijkstra explained. This suggests that the brain may be summing up both real and imagined stimuli in a way that influences what we believe we are seeing.
Another region, the anterior insula, showed activity only when participants reported the stripes as real. This region is known to play a key role in integrating and filtering sensory information. Its selective activation suggests it may act as a cognitive gatekeeper, helping us separate internal imagery from external perception.
Implications for Mental Health and Future Research
The study provides crucial groundwork for understanding conditions such as psychosis, where individuals may struggle to distinguish between internal thoughts and external reality. Naselaris noted that although the findings are promising, future research must consider other cognitive factors, such as attention and memory, that might affect participants’ self-reports.
Both Dijkstra and Naselaris emphasized the importance of expanding this research to include more complex visuals — such as faces and natural scenes — to better understand how these brain regions function in everyday perception. Such insights could eventually help explain visual hallucinations and inform therapies for psychiatric disorders.
This research, along with recent work featured in Nature on brain–computer interfaces decoding speech from neural signals, illustrates how neuroscience is rapidly advancing our understanding of the mind’s inner workings — blurring the boundary between thought and reality.
