In 1956, British psychiatrist Humphry Osmond coined the word “psychedelic” from Greek roots meaning “mind-manifesting” or “soul-revealing.” The term proved fitting. Users report that seconds stretch into eternity, sounds turn into color, and you very self begins dissolving. And now, after decades in scientific exile, those same once-ostracized compounds are undergoing a dramatic scientific renaissance. Researchers are investigating them not only for depression, trauma, and addiction, but also as a potential window into one of neuroscience’s deepest mysteries: how the brain constructs reality itself. And a small, egg-shaped structure buried deep in the center of the brain, the thalamus, may play an important role in that process.

Scientists once viewed the thalamus largely as a relay station: a kind of biological switchboard routing sensory information to the cortex, the brain’s outer layer responsible for higher thought, perception, and conscious awareness. But newer theories suggest something far stranger. Increasingly, neuroscientists suspect reality may partly reflect the brain’s constantly updated “best guess” about the world—built from memory, expectation, sensory input, and context, as Michelle J. Redinbaugh, PhD, a neuroscientist at Stanford University, puts it.

In a 2024 review published in Neuron, Redinbaugh and colleagues examined evidence from anesthesia, sleep, coma studies, perception experiments, and deep brain stimulation research to better understand the thalamus’s role in awareness. They came to a striking conclusion: The structure may help shape not only whether we are conscious, but also how awareness itself feels from moment to moment: unified, continuous, and stable—rather than fragmented into disconnected sensory pieces.

“… What you are seeing, hearing, smelling, what your internal state is like, how your body feels. All these sorts of things coalesce into consciousness,” Redinbaugh says. The thalamus sits in a loop between many cortical regions, continuously coordinating integrated information across the brain. Without that stabilizing process, she says, experience could feel fragmented “like a bunch of boxes.”

“You could call it a compression in terms of data science,” Redinbaugh says, describing how this small ovoid hub condenses massive amounts of sensory information into a continuous stream of awareness. The brain’s ordinary mode of operation constantly screens and constrains perception. Evolution likely favored such filtering because processing every detail of reality in full precision would be catastrophically inefficient. If allowed in, the gargantuan soup of sensory stimuli out there could overwhelm the brain’s ability to offer us a seamless sense of self, pushing the system toward total breakdown. And the brain chose speed over perfection—or variety.

Redinbaugh points to vision itself as an example: humans only see sharply in a tiny central region of the eye, while the brain reconstructs much of the periphery using assumptions and predictions. Evolution may have selected for that tradeoff because taking in every detail of the visual world in infinite detail would be mentally chaotic and energetically unsustainable. Without these shortcuts, reality itself could arrive as an unbearable sensory avalanche.

But the thalamic gatekeeping system does have its own weak spots. Anesthesia is one of them. Under it, thalamic activity shifts into disrupted “on/off” rhythms that may destabilize the coordinated neural activity supporting awareness, Redinbaugh says. The seamless experience we normally take for granted may begin to fracture in those moments.

Psychedelics are now exposing another crack in the system.

In a massive 2026 mega-analysis published in Nature Medicine, researchers analyzing brain scans across multiple psychedelic drugs found widespread shifts in communication across large-scale brain networks, including networks involving the thalamus. Brain systems that normally remain relatively segregated appeared to interact in unusual and sometimes intensified ways.

Though Redinbaugh stresses that neuroscience is still evolving, she admits it is reasonable to think hallucinogens alter the reciprocal relationship between higher brain networks and the thalamus. These drugs generally increase cortical excitability, which then feeds back into the deep-brain structure itself. One influential theory, she explains, is that psychedelics effectively make the brain’s normal “rules” more lenient.

“If you are now tweaking how the thalamus interacts with cortex, and cortex is more excitable, and you have kind of this loosening… suddenly you’re in a situation where you can no longer use the rules to constrain your perception,” she continues. “And then you’re also increasing this sort of bottom-up activity that is telling you what you’re seeing, so all of a sudden you see a lot of weird stuff, or you experience a lot of weird stuff.”

But what exactly is this “weird stuff” psychedelics seem capable of unleashing when they tamper with the brain’s reality-gating systems? For some, they may be aspects of perception normally hidden from conscious awareness. Could they be signs of “higher consciousness?”

Redinbaugh isn’t quite ready to call it that. “But it’s certainly a very different state of consciousness,” she adds.

Others are even more skeptical of the phrase “higher consciousness.”

“It implies a single scale, and it’s not clear what that scale would measure,” says Anne-Laure Le Cunff, PhD, a neuroscientist at King’s College London. Different forms of awareness, she argues, may involve different dimensions, like attention, memory, perception, wakefulness; they don’t exist on a simple ladder from lower to higher. Psychedelics may feel expansive or meaningful, she says, but “that doesn’t make them globally higher or more conscious.”

Part of that expansiveness may stem from the way altered states appear capable of distorting some of the brain’s most fundamental organizing systems such as time—processes in which the thalamus itself may play a central role, according to James M. Shine, PhD, a professor of systems neuroscience at the University of Sydney, who worked with Redinbaugh on the 2024 Neuron review.

One reason may be biochemical, he says. This integrative node and its cortical inputs are densely covered in 5-HT2A serotonin receptors, the primary receptors through which classic hallucinogenic drugs exert many of their effects. At the same time, Shine continues, the thalamus appears deeply involved in coordinating neural activity across radically different timescales, from the milliseconds required to perceive an image to massive state changes like the transition between wakefulness and sleep.

The implications quickly become existential. If the brain actively builds stable reality by orchestrating perception, time, and prediction, what happens if humans eventually learn to deliberately tweak those systems?

“Who is to say that this isn’t already the mechanism by which we learn to navigate our perceptual [subjective world] as our brains develop over our life spans?” Shine says. Of course, neuroscience doesn’t yet understand how awareness emerges from the brain. This does not deter Shine from saying that the developing brain may already provide natural examples of what scientists call “thalamocortical gain modulation,” though—suggesting that lived experience may leave lasting biological imprints on the neural machinery through which we experience the world.

For Redinbaugh, years spent studying consciousness seem to have left their own imprint on how she views the subject. As a young researcher, she once saw consciousness as uniquely human. Now, she says, it seems increasingly likely that animals such as rats possess their own vastly different forms of experience. Mammalian brains appear capable of generating rich subjective experience with remarkable energy efficiency, something even the world’s most advanced artificial intelligence systems still struggle to replicate, she says. And the deeper scientists probe consciousness, the more the question spills beyond neuroscience into ethics, medicine, and society itself, from animals to coma patients unable to communicate their awareness.

“Consciousness has a very important sociological role… How do we protect the most vulnerable among us who cannot easily explain that they’re conscious?” asks Redinbaugh.

“The more you learn about consciousness,” she says, “the more you really equate it with life, or what gives life value.”