imagindi

Mind & Cognition

Simulation Theory · Neuroscience

What If Reality and Imagination Are the Same System?

Perception feels like contact with the world. Imagination feels like a private escape from it. The newest neuroscience — down to individual neurons — suggests the line between them is a gradient, not a wall.

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We usually treat perception as contact with the external world and imagination as a private mental exercise. But the more closely neuroscientists look, the thinner that boundary appears. Work on visual mental imagery shows that imagining something recruits many of the same brain systems used to perceive it, remember it, and plan around it. Seeing and picturing are not opposite processes. They are variations on a single constructive act.

Older models of the mind often treated perception as passive reception, as though the brain simply recorded whatever light and sound arrived at the senses. That picture has been challenged for decades. Richard Held argued that perception is better understood as an active process, one the brain builds rather than simply receives.¹ Contemporary overviews of the field still frame perception this way: as a cognitive achievement assembled from incomplete and ambiguous sensory data, not a straightforward readout of the world.¹¹ Joel Pearson's influential review extends this logic to imagery itself, describing it as a distributed network spanning frontal and sensory regions, overlapping with the brain's default mode network, and functioning, in his words, like a weak form of perception.² Both seeing and imagining, in other words, depend on the brain's ongoing constructive activity — they simply differ in how tightly that activity is constrained by incoming sensory evidence.

01Imagination Is Built From Memory

Imagination is not free-floating fantasy. Daniel Schacter, Roland Benoit, and Karl Szpunar define episodic future thinking as the capacity to imagine or simulate experiences that might occur in one's personal future, and they show it draws on the same mechanisms that support episodic memory.³ Pearson's review reaches a similar conclusion from the imagery side, emphasizing that mental imagery is closely tied to memory recall and other cognitive functions.² Picture a future conversation, a vacation, or a worst-case scenario, and you are not generating something from nothing. You are recombining stored experience into a new configuration.

The hippocampus sits at the center of that recombination. Rather than acting as a passive storehouse of memories, recent models describe it as an engine of memory construction, reconstruction, and generative scene-building.⁴ Kai Jensen, Guillaume Hennequin, and Marcelo Mattar go further, modeling planning itself as a process of sampling imagined action sequences, with hippocampal replay-like activity emerging naturally from a recurrent network trained to plan.⁵ Memory, imagination, and planning appear to share the same underlying machinery for constructing possible scenes and possible actions.

Imagination is not the opposite of memory. It is memory run forward, loosened from its original constraints and pointed at a scenario that hasn't happened yet.

This overlap also helps explain a familiar but strange fact: mentally rehearsing a task can shape how well you later perform it. If planning and imagery both activate the systems involved in selecting and simulating action, then imagined practice is not merely motivational self-talk — it is, in a real sense, engaging the same circuitry that will later execute the movement or decision. That capacity also varies enormously between people: Pearson notes a spectrum running from aphantasia, where visual imagery is absent or extremely faint, to imagery so vivid it can be difficult to distinguish from perception.²

the newest evidence

02How the Brain Tells Them Apart — When It Can2023–2026

If imagination and perception share so much machinery, how does the brain usually keep them straight — and what happens when it can't? A 2023 study from UCL directly tested this. Nadine Dijkstra and Stephen Fleming had over 600 participants imagine simple visual patterns while a real version of the same pattern was gradually faded into view without their knowledge. The two signals blended together in participants' minds: vivid imagining made people more likely to believe something real was on screen, and real stimuli were sometimes mistaken for an unusually strong burst of imagination.⁶ Their conclusion, echoed almost word for word in the paper's abstract, is that there is no categorical difference between imagination and reality — only a difference of degree.

A 2025 follow-up in Neuron pinned that difference down to a specific mechanism. Dijkstra, Thomas von Rein, Peter Kok, and Fleming found that judgments of reality track the combined strength of activity in the fusiform gyrus, a region that lights up during both seeing and imagining. When imagined and real signals in that region reach similar intensity, people confuse the two; a connected region, the anterior insula, appears to read out this "reality signal" to produce a final yes-or-no judgment.⁷ In effect, the brain doesn't have a separate channel for "real" versus "imagined" — it has a volume dial, and reality is what crosses a threshold.

The most direct evidence yet came in early 2026, at the level of single neurons. Recording directly from electrodes implanted in the human brain, Vishnu Wadia and colleagues at Cedars-Sinai and Caltech found that roughly 80% of visually responsive neurons in the ventral temporal cortex encode objects using a shared "axis code," and that around 40% of those same neurons reactivate that exact code during imagery alone, with no image on screen.⁸ The overlap Pearson and others had mapped at the level of brain regions turns out to hold down to individual cells: imagining an object substantially means switching back on the very neurons that once saw it.

the simulation question

03What This Does — and Doesn't — Say About "Simulation"

None of this proves the universe is a simulation. Nick Bostrom's well-known argument is a philosophical proposal about the statistical odds that a sufficiently advanced civilization would run many "ancestor simulations," not a claim derived from neuroscience.⁹ Conflating the two does the neuroscience a disservice. A recent evolutionary and computational account by Orit Zacks and Eva Jablonka instead frames imagination as a biological adaptation: a generative capacity that evolved because simulating possible scenes and actions internally is cheaper and safer than testing them in the world.¹⁰

What the neuroscience does support is a more modest, but still striking, claim: the brain itself constructs experience through predictive, generative processes, and the newest work shows this down to the level of firing neurons and measurable "reality thresholds." In that specific sense, lived reality is already partly simulated from within, well before any question about the nature of the universe as a whole. Perception, memory, future thinking, and imagination look less like separate mental departments and more like related modes of one internal construction process.

Seen this way, imagination is not the opposite of reality — it is one of the brain's tools for testing possibilities, integrating memory, and preparing for action under uncertainty. Reality is the version of this constructive process most tightly bound to sensory evidence and shared conditions; imagination is the version with looser constraints and more room to recombine. The distinction survives. It is simply a difference of degree, not a hard divide.

—References

1. Held, R. (1989). Perception and its neuronal mechanisms. Cognition, 33(1–2), 139–154. doi.org/10.1016/0010-0277(89)90008-5
2. Pearson, J. (2019). The human imagination: the cognitive neuroscience of visual mental imagery. Nature Reviews Neuroscience, 20(11), 624–634. doi.org/10.1038/s41583-019-0202-9
3. Schacter, D. L., Benoit, R. G., & Szpunar, K. K. (2017). Episodic future thinking: mechanisms and functions. Current Opinion in Behavioral Sciences, 17, 41–50. doi.org/10.1016/j.cobeha.2017.06.003
4. Spens, E., & Burgess, N. (2024). A generative model of memory construction in the hippocampus. Nature Human Behaviour, 8, 546–561. doi.org/10.1038/s41562-023-01799-z
5. Jensen, K. T., Hennequin, G., & Mattar, M. G. (2024). A recurrent network model of planning explains hippocampal replay and human behavior. Nature Neuroscience, 27(7), 1340–1348. doi.org/10.1038/s41593-024-01675-7
6. Dijkstra, N., & Fleming, S. M. (2023). Subjective signal strength distinguishes reality from imagination. Nature Communications, 14, 1627. doi.org/10.1038/s41467-023-37322-1 PMC10036541 UCL News summary
7. Dijkstra, N., von Rein, T., Kok, P., & Fleming, S. M. (2025). A neural basis for distinguishing imagination from reality. Neuron, 113(15), 2536–2542.e4. doi.org/10.1016/j.neuron.2025.05.015
8. Wadia, V. S., Reed, C. M., Chung, J. M., Bateman, L. M., Mamelak, A. N., Rutishauser, U., & Tsao, D. Y. (2026). A shared code for perceiving and imagining objects in human ventral temporal cortex. Science, 392, 207–215. doi.org/10.1126/science.adt8343
9. Bostrom, N. (2003). Are We Living in a Computer Simulation? The Philosophical Quarterly, 53, 243–255. doi.org/10.1111/1467-9213.00309
10. Zacks, O., & Jablonka, E. (2026). The neural basis of imagination: An evolutionary and computational perspective. Trends in Cognitive Sciences. doi.org/10.1016/j.tics.2026.01.004
11. Kumar, P. (2026, April 11). The Scientific Explanation of Perception: A Cognitive Perspective. Philosophy Institute. philosophy.institute

Imagindi · Mind & Cognition