A new hypothesis proposes that our basic sense of being conscious—the “me inside”—originates in the brainstem, an evolutionarily ancient part of the brain. Drawing on evidence from pain research, brain injuries and anesthesia, the researchers suggest that the cerebral cortex processes much of the information we experience, while brainstem circuits make that information consciously felt. The paper offers a different direction for investigating one of science’s most enduring mysteries.

Close your eyes and cover your ears. Much of the world around you disappears from view and hearing, yet your sense of being present, of being conscious, remains. What creates that basic feeling of being “you”?

A hypothesis paper published in The Neuroscientist by Prof. Marshall Devor of the Hebrew University of Jerusalem and Dr. Mark Baron of the Hebrew University and Harvard Medical School proposes that the answer lies deep in the brainstem.

Their argument challenges approaches that place the source of conscious experience primarily in the cerebral cortex—the brain’s folded outer layer, responsible for complex functions including language, recognition and planning. Instead, they suggest that the basic capacity to feel and experience originates in older “primitive” brainstem circuitry.

The paper brings together existing experimental findings and clinical observations to develop this theory. It does not claim to establish a proven mechanism for consciousness.

Why pain may hold a clue
The researchers build their argument around a familiar experience: pain.

Detecting a harmful stimulus and feeling pain are different things. The nervous system can trigger an automatic "reflexive" withdrawal from danger, but pain also involves a subjective experience: it hurts.

Devor and Baron argue that evidence from brain stimulation, epileptic seizures, neurological injuries and other research suggests that this feeling does not depend on the cortex in the same way that complex visual or auditory experiences do.

For example, they point out that even extensive cortical damage usually leaves pain experience intact, or even increased, while such damage can severely degrade vision and hearing. Loss of consciousness is rare. In contrast, damage to particular brainstem regions consistently causes coma. In their interpretation, these differences suggest that the brainstem may do more than just keep the cortex awake: it may generate the basic capacity for conscious experience of pain, and by extension also the other senses.

Processing information—and consciously experiencing it
The theory distinguishes between the information the brain processes robotically, like a self-driving car, and the feeling of consciously experiencing that information.

Recognizing a face, understanding a sentence, or identifying that an animal might attack, requires sophisticated processing. The researchers propose that the cortex performs most of this work. In addition, the cortex evaluates what benefit or danger might ensue. Based on this information, brainstem circuitry adjudicates which sensory streams should enter conscious experience and receive priority attention from “you”, and which should remain unattended.

This distinction could help explain why damage to particular cortical regions can remove specific abilities, such as seeing or recognizing objects, without necessarily eliminating the person’s basic awareness.

Under this model, the cortex and brainstem work together: the cortex supplies detailed information about the world, and brainstem mechanisms shine the light of subjective experience on those aspects that merit conscious attention.

An ancient foundation for the conscious mind

The paper also offers an evolutionary explanation of this task sharing.

The researchers propose that the capacity to experience pain arose as an add-on to reflexive responses to harmful stimuli, like a predator’s bite. This addition arose early in evolution. It does not take a cortical supercomputer to determine that tissue injury if bad. As brains became more complex, the expanding cortex gained increasingly more sophisticated abilities to interpret the survival significance of sights, sounds, smells and other information.

Rather than developing an entirely separate system for conscious experience to serve the progressively expanding cortex, they suggest that evolution adopted the brainstem machinery long associated with conscious experience of pain.

In this account, the most basic feeling of being conscious has ancient roots, while the richness of what we humans experience reflects the later development of more powerful information processing.

A direction for future research
The authors draw particular attention to a region of the brainstem called the mesopontine tegmentum, where previous research has identified circuits involved in coma following brain injury and loss of consciousness during surgical anesthesia.

They argue that investigating this area and its connections could help researchers test the brainstem theory and explore how neural activity becomes subjective experience.

However, while the precise mechanism remains unresolved, it is surely biological. The paper proposes a framework for further investigation rather than a completed explanation of how the brain generates consciousness.

Ultimately, Devor and Baron call for greater attention to the brainstem in the search for how the brain creates our most basic experience: being here, feeling something, and knowing the world from the inside.