Neuroscientists Uncover Brain Regions That Distinguish Real Images from Imagined Ones

Neuroscientists have developed a method to understand how the brain differentiates between real and imagined images. Despite both types of imagery being processed using the same neural systems, most people can easily tell the difference between what they see and what they imagine. A new study, published in Neuron on June 5, identifies two brain regions responsible for this distinction, offering insights into a critical aspect of cognitive function. “Separating our inner thoughts from the external world is essential for everyday functioning,” explains Nadine Dijkstra, a cognitive neuroscientist at University College London. “However, this ability can falter in conditions like psychosis and schizophrenia,” she adds. Dijkstra and her team devised an innovative approach to explore the limits of this mental distinction. Volunteers were shown black and white stripes of varying transparency superimposed on a background similar to television static. In certain trials, participants were asked to imagine the stripes and report whether they perceived them as real and how vividly they appeared. The team found that participants were more likely to report the stripes as real when they appeared more vivid, regardless of their actual presence. Thomas Naselaris, a neuroscientist at the University of Minnesota Twin Cities, notes that this research aims to quantify and model an abstract concept—the interaction between imagination and vision. Previously, this question was more philosophical than empirical. To link the participants' perceptions to brain activity, the researchers used functional magnetic resonance imaging (fMRI). This technique tracks changes in blood flow, which serves as a proxy for brain activity. During the experiments, fMRI scans revealed that activity in the fusiform gyrus strongly correlated with the reported vividness of the stripes. The fusiform gyrus, known for processing high-level visual information, plays a previously undiscovered role in this cognitive task. According to Dijkstra, the fusiform gyrus seems to integrate both real and imagined stimuli, creating a "reality signal" or "vividness signal." This signal helps predict whether participants will judge an image as real. “The fusiform gyrus appears to be the brain's way of keeping track of how vivid an image feels, which in turn influences our perception of reality,” she explains. These findings have significant implications for understanding cognitive disorders where the distinction between reality and imagination breaks down. By identifying the specific brain regions involved, researchers can develop better diagnostic tools and treatments for conditions such as psychosis and schizophrenia.