People in a coma are aware of the world around them thanks to “hidden consciousness”


Speaking about the state of consciousness during a coma, in Scientific American magazine, are professors Jan Claassen, an associate of neurology at Columbia University and neurologist in intensive care at New York-Presbyterian Hospital of Columbia University, and Brian L. Edlow, an associate of neurology at Harvard Medical School and a critical care neurologist at Massachusetts General Hospital, where he directs the Laboratory for Neuroimaging of Coma and Consciousness.


To introduce the theme, they tell the story of a 30-year-old girl, Maria Mazurkevich, who was admitted to Columbia University’s New York-Presbyterian hospital because she had suffered a ruptured blood vessel in her brain and the hemorrhage exerted strong pressure on brain regions criticisms. The girl, in a coma, was attached to a mechanical ventilator that helped her breathe and her vital signs were stable. But she showed no signs of consciousness. The doctors, also to comply with the request of Maria’s parents, asked Mazurkevich to open his eyes, lift two fingers or move his toes, but she, as could be imagined, remained motionless. Her eyes didn’t follow the visual cues. “And yet, her loved ones still thought she was “in there,” the professors write. “She. She was.”, They then add.

The medical team did an Encephalon Gram (placement of sensors on the head to monitor the electrical activity of the brain) while they asked her to “keep opening and closing her right hand.” Then they asked her to “stop opening and closing her right hand.” Although her hands did not move, the brain reactions recorded by her EEG clearly indicated that she was aware of her requests and that they were different. After about a week, her body started following her brain. Slowly, with minimal responses, Mazurkevich began to wake up. Within a year she made a full recovery with no major limitations to her physical or cognitive abilities.

The professors go on to write that Mazurkevich exhibited a ” hidden consciousness ,” a state in which the brain reacts to the outside world with some understanding, even if the body is unresponsive. The 15-20% of patients who appear to be in a coma, or other unresponsive state, show these internal signs of awareness when evaluated with advanced brain imaging methods or sophisticated electrical activity monitoring. Many of these techniques have only recently been perfected.


“These methods are changing our understanding of coma and other disorders of consciousness. These findings, which a few decades ago would have baffled most neurologists and neuroscientists, highlight the importance of recognizing this hidden conscious state and developing ways to communicate with the people in it,” write Drs Claassen and Eldow



To diagnose the hidden state of consciousness, doctors ask the patient to open and close their hands or imagine swimming, while recording their brain reactions with an EEG or functional magnetic resonance imaging. These responses have been reproduced by different research groups around the world, despite methodological differences. Patients with hidden consciousness can alter their brain patterns when asked to move parts of the body or imagine an activity. But outwardly, in terms of bodily movements, they don’t show that they follow any prompts. Recent studies suggest that brain injuries that disconnect the thalamus – a region that transmits movement signals and sensory information between the body and the brain – from the cerebral cortex, responsible for higher-level cognitive functions, may be responsible for this semi-conscious condition. However, it is likely that not a single type of injury, but rather various combinations of injuries at different locations, could cause motor dysfunction and allow for hidden consciousness.


Current limits and the “Curing Coma Campaign”

This state of being in which cognitive function surpasses motor expression is still poorly understood and both EEG techniques and functional magnetic resonance have limitations . The methods may miss intentional brain activity in some patients who later regain consciousness. MRI scans only provide a snapshot of a patient’s level of consciousness during a short time , because it cannot be easily repeated. EEG can be performed frequently at the patient’s bedside, capturing snapshots at different times, but this method has its shortcomings. Its readings may be skewed from electrical noise created by other machines in intensive care rooms, which can cause the test to reflect artifacts rather than reality.

Both methods need improvement, but the evidence for their utility is strong enough to be approved for the diagnosis of covert consciousness in clinical guidelines in the United States (in 2018) and Europe (in 2020) . Furthermore, early detection of hidden consciousness, soon after a patient’s injury, predicts behavioral recovery of consciousness, long-term functional recovery, and the speed of that recovery, as demonstrated by research the professors published together with their research team, in 2019 (ec onfirmed more recently, in 2022 ).

Based on these studies, in 2019 scientists came together to launch the Curing Coma Campaign , an international collaboration led by the Neurocritical Care Society to direct medical resources and public attention to this condition, with the aim of developing new therapies that promote the recovery of consciousness. Neurologists are trying to develop a test that can identify patients who are likely to be in a hidden state of consciousness and therefore should undergo advanced EEG and functional MRI assessments.


Further complicating clinical efforts to detect semiconsciousness is the fact that patients with severe brain injury often exhibit fluctuating levels of consciousness . Such swings mean that an individual valuation may miss important signals.

The brain-computer interfaces

People in a coma are aware of the world around them thanks to "hidden consciousness"

Based on recent discoveries about the presence of hidden consciousness, researchers are trying to reconnect and communicate with these patients using brain-computer interfaces . These devices typically record the electrical activity of the brain as it asks the patient to move a mouse cursor on a computer screen. The computer “learns” to identify the physiological signals related to the patient’s attempts to move the cursor left, right, up or down. Once training is complete, these brain patterns allow the patient to take control of the cursor. Patients can use it to select letters and spell words.

Brain-computer interfaces would be ideal for providing conscious patients with a communication channel to the outside world. But enormous challenges must be overcome, particularly for patients with acute brain injury. Also, the busy and noisy environment of the ICU is not ideal for these purposes.

To further improve communication, reliable tools are needed to identify patients in a hidden state of consciousness. Some groups are investigating advanced EEG technology, which can be more easily integrated into the clinical routine of an intensive care unit. Furthermore, with brain-computer interfaces, the accuracy of the algorithm that decodes patient attempts to control the device could be improved by using additional biological signals , such as heart rate, alongside brain activity.

Brain-computer interfaces have not yet allowed for in-depth conversations, and until now patients with occult consciousness, who recovered the ability to communicate and were interviewed later, did not remember the experience of being semi-conscious. Mazurkevich, for example, does not remember any aspect of his time in the intensive care unit when he appeared to be in a coma. So the experience is still largely a mystery.

“There is no mystery, on the other hand, about the ethical imperative that doctors have today to seek consciousness in patients who don’t seem to react, using all available technologies and resources. Increasing access to these technologies and resources is a key goal and challenge for the medical community, promoted by the Curing Coma campaign. With these tools, we can hope for a future in which all occultly conscious people have the opportunity to speak for themselves ,” conclude the professors.


  • Some People Who Appear to Be in a Coma May Actually Be Conscious. (
  • Practice guideline update recommendations summary: Disorders of consciousness. (
  • Cognitive-motor dissociation and time to functional recovery in patients with acute brain injury in the USA: a prospective observational cohort study. The Lancet Neurology. (


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