Study Shows People Use Same Neurons to See and Imagine Objects

Why can images of things we have seen seem so real when we later recall them from memory? A new study led by Cedars-Sinai Health Sciences University investigators sheds light on the answer.

The study shows that the same brain neurons are activated when we imagine something and when we perceive something. The research, led by Cedars-Sinai, is the first to provide a detailed understanding of the shared mechanism that underlies visual perception and creation of mental images in the human brain. It was published in the journal Science.

"We generate a mental image of an object that we have seen before by reactivating the brain cells we used to see it in the first place," said Ueli Rutishauser, PhD, director of the Center for Neural Science and Medicineand professor of Neurosurgery, Neurology and Biomedical Sciences at Cedars-Sinai Health Sciences University, and the study's joint senior author. "Our study revealed the code that we use to re-create the images."

The findings provide a biological basis for visual imagination, a process that is also critical for creative arts.

"Further insight into this neural process has the potential to open pathways toward developing new therapies for post-traumatic stress disorder, obsessive-compulsive disorder, and other mental conditions that involve uncontrolled vivid imagery," said Adam Mamelak, MD, director of the Functional Neurosurgery Program and professor of Neurosurgery at Cedars-Sinai, and co-author of the study.

To conduct the study, investigators asked 16 adults with epilepsy, who had electrodes temporarily implanted in their brains for diagnosing their seizures, to view a series of images of faces and objects. After viewing them, a subset of the participants were asked to imagine those same images from memory. Meanwhile, researchers recorded the electrical activity of hundreds of individual neurons in each participant's brain.

When the patients viewed the images, neurons were activated in their fusiform gyrus, an area of the brain essential for high-level visual processing, particularly for faces. For 80% of the visually responsive neurons recorded in the study, the researchers uncovered the aspects of the images they reacted to, thereby revealing their neural code. When the patients later imagined the images, about 40% of these neurons reactivated using the same code, thereby recreating the pattern of activity that occurred during the initial viewing of the images.

"Advanced artificial intelligence tools were critical to our investigation at all stages," said Varun Wadia, PhD, a postdoctoral scientist in Rutishauser's laboratory and first author of the study. "We used deep visual neural networks to create numerical descriptions of objects so that we could understand the neurons' code. We then verified the code by using generative AI to create never-before-seen images and correctly predict the brain's responses to these images."

The research builds on the work of Doris Y. Tsao, PhD, of the University of California, Berkeley, who is co-senior author on the study. She identifed the neural code for object recognition in nonhuman primates. The current study reveals that the same neural code is present in humans and that it explains visual imagination.

"These findings support the idea that imagining and seeing share a common neural code and may have important implications for understanding psychiatric disorders marked by disruptions in mental imagery and reality discrimination," said Hermon Gebrehiwet, DrPH, program officer at the National Institutes of Health.

Still to be determined are what triggers the neural reactivation the investigators found, and how memories lead to reactivation of just the right subset of neurons needed, the investigators said.

Other Cedars-Sinai authors include: C. M. Reed, J. M. Chung, and L. M. Bateman

Funding: The work was supported by the National Institutes of Health's Brain Research Through Advancing Innovative Neurotechnologies® Initiative, or The BRAIN Initiative® (U01NS117839 to UR), the Howard Hughes Medical Institute (DYT), the Simons Foundation Collaboration on the Global Brain (UR and DYT) and the Chen Center for Systems Neuroscience at Caltech (DYT).

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