LOS ANGELES, CALIFORNIA — Imagined and perceived objects activate the same neurons and use the same neural code in the human brain, according to a study published in the journal Science by Varun Wadia, a brain scientist at Cedars-Sinai Medical Center and the California Institute of Technology, and his colleagues. The findings came from recordings of 16 patients with epilepsy who had electrodes implanted in their brains to locate the source of their seizures.

Wadia's team monitored the activity of more than 700 individual neurons in each participant as they watched a computer screen. In the first part of the experiment, participants saw hundreds of images from categories including faces, animals, plants and words, as well as small objects like sunglasses and water bottles. The team focused on neurons in the ventral temporal cortex, which is involved in recognizing objects, and recorded which neurons fired in response to each image, noting the number of times each neuron fired to decipher the neural code used to convey information about an image.

In the second part of the experiment, participants closed their eyes and imagined one of the objects they had seen. About 40% of the neurons that had been active when participants saw an object reactivated with roughly equal strength when they imagined that object. The pattern of neural activation was distinctive enough to identify the specific object a participant was imagining, including details such as size, angle and whether the object was inside or outside.

The result supports earlier studies using brain imaging that found the same neural circuits are involved in seeing and imagining. Technologies like functional MRI, however, cannot show what individual neurons are doing. "This has not been demonstrated before at the neural level," said Kalanit Grill-Spector, a psychology professor at Stanford University's Wu Tsai Neurosciences Institute. According to Grill-Spector, the new findings bring scientists closer to building computer models that can simulate vision and vision disorders like macular degeneration. Such models could help researchers develop prosthetic devices to restore sight.

Thomas Naselaris, a neuroscientist at the University of Minnesota, said the research explains how the brain uses imagination to augment visual information. "Objects are three-dimensional. They present themselves to us one side at a time, and yet we intuitively seem to be able to model the parts of the object we don't see," he said. Visual imagination also allows people to assemble familiar objects into unfamiliar configurations.

Doris Tsao, a University of California, Berkeley professor and an author of the study, had previously conducted research showing how the visual system of monkeys recognizes faces and other objects. The study does not explain the brains of people with aphantasia, a condition that leaves them unable to voluntarily summon mental images. Because the findings are based on recordings from epilepsy patients, they may not generalize to healthy brains.