The ability to conjure a vivid image in the mind’s eye—whether it is the layout of a childhood home or the face of a loved one—is a fundamental component of human cognition. This internal visualization allows people to navigate the physical world, plan for the future, and create art. For decades, scientists have suspected that the brain uses the same machinery to “see” an object as it does to “imagine” one, but the exact cellular mechanism remained elusive.
A new study published April 9 in the journal Science provides some of the most direct evidence to date that seeing and imagining activate some of the same brain cells. By recording the activity of individual neurons in real-time, researchers found that the brain does not simply use the same general region for both processes, but often reactivates the specific neural code used during the original perception of an object.
The findings offer a glimpse into the “generative model” of the human brain, suggesting that mental imagery is essentially a controlled reactivation of sensory experiences. This discovery has implications that extend beyond basic neuroscience, potentially offering new pathways for treating psychiatric conditions where the boundary between perception and imagination becomes blurred.
Mapping the Ventral Temporal Cortex
To understand how mental imagery works, researchers needed to observe the brain at a granular level. While functional MRI (fMRI) scans can demonstrate which general areas of the brain are active, they lack the resolution to track individual neurons. To overcome this, a team led by Ueli Rutishauser, a neuroscientist at Cedars-Sinai Medical Center in Los Angeles, collaborated with patients who already had medical electrodes implanted in their brains.
The study involved 16 adults with epilepsy. These participants had electrodes temporarily placed in their brains to help clinicians locate the origin of their seizures, providing a rare clinical window into the ventral temporal cortex—a region critical for representing and recognizing visual objects.
During the study, participants viewed hundreds of images across five distinct categories: faces, text, plants, animals, and everyday objects. The researchers recorded the activity of more than 700 neurons. They discovered that approximately 450 of these neurons were selectively responsive to specific categories. Using machine learning, the team further determined that 80 percent of these category-responsive neurons were tuned to specific visual features within the images, rather than just the general category.
The Overlap Between Sight and Thought
The core of the research focused on what happens when the external stimulus is removed. Six of the participants were asked to conjure mental images of the objects they had previously viewed. The results revealed a striking overlap: about 40 percent of the neurons that were active when the participants were actually seeing the objects responded in a similar way when the participants simply imagined them.
This suggests that the brain does not create a separate “imagination” circuit. Instead, it re-uses the same cellular hardware that processes real-world vision. To validate these findings, the researchers used the recorded neural data to actually reconstruct the pictures the participants were recalling, effectively “reading” the mental image from the brain’s electrical activity.
Nadine Dijkstra, a neuroscientist at University College London who was not involved in the study, noted that while the field had long operated on the assumption that perception and imagination shared a neural basis, this specific evidence had been missing. Dijkstra described the work as a study that the field had been waiting for.
Key Findings of the Neural Imagery Study
| Metric | Observation | Significance |
|---|---|---|
| Neuronal Overlap | ~40% of neurons | Direct evidence that the same cells handle seeing and imagining. |
| Feature Selectivity | 80% of responsive neurons | Imagination is based on specific visual features, not just general ideas. |
| Brain Region | Ventral Temporal Cortex | Confirms this area as a hub for both sensory and mental imagery. |
Clinical Implications for Mental Health
Beyond the theoretical interest in how we reckon, the ability to distinguish between perceived and imagined imagery is vital for mental stability. When the brain’s generative model malfunctions, the result can be a breakdown in the ability to tell the difference between an internal thought and an external reality.
Varun Wadia, a neuroscientist at Cedars-Sinai and study coauthor, pointed out that disruptions to mental imagery are often linked to psychiatric conditions. In cases of schizophrenia, for example, internal imagery may be perceived as external hallucinations. Similarly, in Post-Traumatic Stress Disorder (PTSD), intrusive “flashbacks” are essentially involuntary, high-intensity reactivations of the neural code from a traumatic event.
By understanding the specific neuronal underpinnings of these processes, clinicians may eventually be able to develop targeted therapies to help patients regulate these involuntary reactivations or strengthen the brain’s ability to categorize imagery as “imagined” rather than “seen.”
The Boundaries of Imagination
While the study provides a clear mechanism for recalling existing images, it leaves open the question of how we create things that have never existed. The current research focused on the reactivation of known objects, but the human mind is also capable of “dreaming up” novel visual art or imagining futuristic landscapes.
Rutishauser noted that it remains to be seen whether the same mechanisms are at play during the creation of entirely new imagery. However, the discovery that the brain uses a generative model for recall provides a strong hypothesis for how the brain might combine and rearrange existing neural codes to synthesize novel images.
Disclaimer: This article is for informational purposes only and does not constitute medical advice. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition.
The research team plans to further explore how these neural circuits interact with other brain regions to facilitate complex creativity and the synthesis of new ideas. Future studies may look at whether these patterns differ in individuals with aphantasia—the inability to visualize mental images.
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