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https://www.psypost.org/neuroscientists-...ciousness/
EXCERPTS: A new theoretical paper proposes that the most basic feeling of being a conscious self originates in the brainstem rather than the outer layers of the brain. By examining how the brain processes pain, anesthesia, and brain injuries, the authors suggest that raw sentience is computed in an ancient subcortical structure, located beneath the cortex, that acts as a gatekeeper for attention. The hypothesis, published in The Neuroscientist, challenges dominant models of the mind that place conscious awareness within the cerebral cortex.
The brainstem is a stalk-like structure at the base of the brain that connects the upper brain to the spinal cord. Leading theories of consciousness locate it in the cerebral cortex, the wrinkled outer layer of the brain responsible for complex thought and language. In the authors’ view, these theories acknowledge the brainstem’s importance but treat it mainly as a power supply that keeps the cortex running. Yet a 2025 adversarial study of human brain activity failed to confirm key predictions of the two leading cortex-centered theories of consciousness, leaving open the question of how and where the brain generates subjective experience.
To address this puzzle, the paper draws on a distinction from philosophy between two types of awareness: access consciousness and phenomenal consciousness. Access consciousness refers to the specific things a person is aware of at any moment, such as sights, sounds, or memories. Phenomenal consciousness, which the authors call raw sentience or the “me inside,” is the underlying feeling of existing as a conscious observer, a presence that remains completely intact even if a person closes their eyes and blocks their ears.
Clinical and animal observations have repeatedly challenged the idea that the cortex creates this raw sentience. For instance, the author of a 2007 review on brain organization argued that children born without a cerebral cortex still display conscious awareness and emotional responses. Similarly, a 2015 clinical case study of a neurological patient found that a person with extensive damage to the brain areas widely believed to process pain could still fully feel and react to painful stimuli.
Tiny disruptions in a specific part of the brainstem can have the opposite effect. In a 2001 rat experiment led by the new paper’s first author, delivering microscopic doses of an anesthetic drug directly into a specific pocket of the brainstem rapidly and reversibly switched off pain responses and other signs of consciousness. The new research, led by Marshall Devor of The Hebrew University of Jerusalem alongside colleague Mark Baron, brings these lines of evidence together into an evolutionary framework proposing that raw conscious feeling originated, and still resides, in the brainstem.
[...] Drawing on these findings, the authors propose an evolutionary model for how consciousness works. When pain fibers in the skin or organs detect tissue damage from a threat like a predator’s bite, that signal already carries direct survival meaning, which the authors call Darwinian fitness valence, as soon as it enters the nervous system. In the authors’ reading, the ancient brainstem evolved sentience hundreds of millions of years ago in early vertebrates to translate these raw tissue-damage signals into the subjective feeling of pain, though they acknowledge there is currently no sure way to know whether fish or reptiles consciously feel pain.
Other senses, such as vision and hearing, do not carry immediate survival meaning at the sensory organ; a pattern of light on the retina could be a harmless cloud or a charging rhinoceros. In the authors’ view, sophisticated analysis of sights and sounds requires the computing power of the mammalian cortex, which evolved roughly 300 million years after early vertebrates, though they acknowledge that animals without a cortex can detect threats by sight and sound at a more basic level. The authors suggest that rather than building a second consciousness system inside the new cortex, evolution wired the cortex down into the existing brainstem consciousness processor.
[...] There are some caveats to consider when evaluating this theory. Much of the brainstem evidence is also consistent with conventional, cortex-centered views, which already hold that the brainstem is needed to keep the cortex awake. Coma after brainstem damage or anesthetic injections does not, by itself, show that subjective experience is generated there. The theory’s distinctive support comes mainly from pain, the one sense the authors argue does not need the cortex.
Even on the question of pain, it is difficult to completely rule out the possibility that when electrical stimulation or seizures in the human cortex occasionally trigger pain, the cortex itself is generating part of that feeling.
[...] In addition, much of the evidence relies on translating findings between nonverbal animals and humans, or interpreting behavior in patients who cannot speak. In experiments with rats or observations of infants born without a cerebral cortex, researchers must infer conscious awareness and pain from physical reactions and vocalizations, which cannot definitively establish what an individual is subjectively experiencing on the inside.
Finally, the paper presents a hypothesis rather than a definitive test... (MORE - missing details)
EXCERPTS: A new theoretical paper proposes that the most basic feeling of being a conscious self originates in the brainstem rather than the outer layers of the brain. By examining how the brain processes pain, anesthesia, and brain injuries, the authors suggest that raw sentience is computed in an ancient subcortical structure, located beneath the cortex, that acts as a gatekeeper for attention. The hypothesis, published in The Neuroscientist, challenges dominant models of the mind that place conscious awareness within the cerebral cortex.
The brainstem is a stalk-like structure at the base of the brain that connects the upper brain to the spinal cord. Leading theories of consciousness locate it in the cerebral cortex, the wrinkled outer layer of the brain responsible for complex thought and language. In the authors’ view, these theories acknowledge the brainstem’s importance but treat it mainly as a power supply that keeps the cortex running. Yet a 2025 adversarial study of human brain activity failed to confirm key predictions of the two leading cortex-centered theories of consciousness, leaving open the question of how and where the brain generates subjective experience.
To address this puzzle, the paper draws on a distinction from philosophy between two types of awareness: access consciousness and phenomenal consciousness. Access consciousness refers to the specific things a person is aware of at any moment, such as sights, sounds, or memories. Phenomenal consciousness, which the authors call raw sentience or the “me inside,” is the underlying feeling of existing as a conscious observer, a presence that remains completely intact even if a person closes their eyes and blocks their ears.
Clinical and animal observations have repeatedly challenged the idea that the cortex creates this raw sentience. For instance, the author of a 2007 review on brain organization argued that children born without a cerebral cortex still display conscious awareness and emotional responses. Similarly, a 2015 clinical case study of a neurological patient found that a person with extensive damage to the brain areas widely believed to process pain could still fully feel and react to painful stimuli.
Tiny disruptions in a specific part of the brainstem can have the opposite effect. In a 2001 rat experiment led by the new paper’s first author, delivering microscopic doses of an anesthetic drug directly into a specific pocket of the brainstem rapidly and reversibly switched off pain responses and other signs of consciousness. The new research, led by Marshall Devor of The Hebrew University of Jerusalem alongside colleague Mark Baron, brings these lines of evidence together into an evolutionary framework proposing that raw conscious feeling originated, and still resides, in the brainstem.
[...] Drawing on these findings, the authors propose an evolutionary model for how consciousness works. When pain fibers in the skin or organs detect tissue damage from a threat like a predator’s bite, that signal already carries direct survival meaning, which the authors call Darwinian fitness valence, as soon as it enters the nervous system. In the authors’ reading, the ancient brainstem evolved sentience hundreds of millions of years ago in early vertebrates to translate these raw tissue-damage signals into the subjective feeling of pain, though they acknowledge there is currently no sure way to know whether fish or reptiles consciously feel pain.
Other senses, such as vision and hearing, do not carry immediate survival meaning at the sensory organ; a pattern of light on the retina could be a harmless cloud or a charging rhinoceros. In the authors’ view, sophisticated analysis of sights and sounds requires the computing power of the mammalian cortex, which evolved roughly 300 million years after early vertebrates, though they acknowledge that animals without a cortex can detect threats by sight and sound at a more basic level. The authors suggest that rather than building a second consciousness system inside the new cortex, evolution wired the cortex down into the existing brainstem consciousness processor.
[...] There are some caveats to consider when evaluating this theory. Much of the brainstem evidence is also consistent with conventional, cortex-centered views, which already hold that the brainstem is needed to keep the cortex awake. Coma after brainstem damage or anesthetic injections does not, by itself, show that subjective experience is generated there. The theory’s distinctive support comes mainly from pain, the one sense the authors argue does not need the cortex.
Even on the question of pain, it is difficult to completely rule out the possibility that when electrical stimulation or seizures in the human cortex occasionally trigger pain, the cortex itself is generating part of that feeling.
[...] In addition, much of the evidence relies on translating findings between nonverbal animals and humans, or interpreting behavior in patients who cannot speak. In experiments with rats or observations of infants born without a cerebral cortex, researchers must infer conscious awareness and pain from physical reactions and vocalizations, which cannot definitively establish what an individual is subjectively experiencing on the inside.
Finally, the paper presents a hypothesis rather than a definitive test... (MORE - missing details)