Levels of Consciousness

At first glance, coma patients may all seem unresponsive, akin to being in a deep sleep. Yet, there are different levels or categories of coma.

A patient is classified as comatose when they are in a profound state of unconsciousness, displaying no response to stimuli such as pain and requiring assistance for basic functions like swallowing. These individuals often depend on machines for survival, and recovery can take weeks or months.

In contrast, those in a vegetative state can breathe independently and do not need life support. Although they may appear to be asleep for extended periods, some may open their eyes or respond to certain stimuli, though these reactions are typically involuntary.

Understanding the distinctions between various states of coma can greatly enhance our knowledge of the human brain. Historically, scientists relied on observable external responses to gauge a patient’s condition, leaving the internal experiences of coma patients largely unknown.

Today, tools such as electroencephalography (EEG) and functional magnetic resonance imaging (fMRI) allow researchers to monitor brain activity in these patients, revealing that several appear conscious despite their immobility.

Cognitive Motor Dissociation

In 2006, the journal Science published a groundbreaking case study on a young woman presumed to be in a vegetative state following severe brain trauma. Neuroscientist Adrian M. Owen and his team employed fMRI technology to explore the patient’s brain activity.

During scans, the researchers prompted her to visualize activities, such as navigating her home or playing tennis. If her brain displayed distinct activity patterns like that of conscious individuals, it would imply awareness despite her external appearance.

To their astonishment, the scans revealed brain responses in the patient similar to those of healthy volunteers, suggesting she could consciously follow instructions. Since this initial study, instances of covert consciousness have been recognized in patients globally with various types of brain injuries.

In 2010, cognitive psychologist Martin Monti adapted Owen’s approach to determine if patients with consciousness disorders could respond to yes or no questions, finding that 5 out of 54 participants were able to consciously modulate their brain activity.

Further findings in 2017 from neurologists at Massachusetts General Hospital indicated that patients in their care exhibited signs of covert consciousness. A subsequent 2019 study from Columbia University and New York University revealed that unresponsive patients showing covert consciousness were about twice as likely to regain some level of independent function within a year post-injury.

These studies represent just a fraction of the ongoing research into covert consciousness. Over the years, scientists have discovered that patients exhibiting this phenomenon can understand language, maintain attention, and remember instructions, despite appearing unresponsive.

While “covert consciousness” is a popular term, many researchers prefer “cognitive motor dissociation,” as it highlights the apparent disconnect between cognitive abilities and motor functions.

Despite accumulating evidence, cognitive motor dissociation is still considered relatively rare, with estimates ranging from 10 to 20 percent of individuals with consciousness disorders. However, a recent comprehensive study suggests that this phenomenon may occur more frequently than previously believed.

New Research

On August 15, 2024, an extensive international collaboration published significant findings in the New England Journal of Medicine, indicating that covert consciousness is more common than earlier assumed. This large-scale study, conducted across six global sites, involved a diverse participant pool and represents the first of its kind to encompass multiple locations.

According to a statement from Mass General Brigham, which co-led the study:

> “This study included participant data from six different sites spanning the United States, United Kingdom, and Europe collected over approximately 15 years.”

In total, 353 individuals with severe brain damage participated in the research. Some were recruited shortly after their injuries, while others had been in long-term care.

The Study

Using the Coma Recovery Scale-Revised (CRS-R), researchers assessed the participants for observable responses to verbal commands. Out of the 353 individuals, 241 showed no apparent response.

All participants underwent EEG and/or fMRI testing. During these assessments, they were instructed to visualize actions like swimming or clenching their fists for brief periods.

The Results

The researchers found that 60 of the 241 participants (about 25 percent) who displayed no outward responses exhibited brain activity comparable to a control group of healthy volunteers. They noted:

> “Cognitive motor dissociation was associated with younger age, longer time since injury, and brain trauma as an etiologic factor.”

Additionally, 43 out of 112 individuals (around 38 percent) with observable responses to commands also demonstrated similar brain activity. Given that vegetative state patients can seem awake but lack awareness, the researchers had anticipated a higher percentage of cognitive motor dissociation in this group.

Lead author Yelena Bodien, PhD, emphasized the importance of these findings:

> “Some patients with severe brain injury do not appear to be processing their external world. However, when assessed with advanced techniques such as task-based fMRI and EEG, we can detect brain activity that suggests otherwise.”

However, researchers caution that EEG and fMRI methods may not capture all instances of cognitive motor dissociation. Notably, the occurrence was more frequently identified when both technologies were used together, suggesting the need for comprehensive testing.

Going Forward

Bodien also highlighted the ethical and clinical implications of the study's findings:

> “These results raise critical ethical, clinical, and scientific questions — such as how can we harness that unseen cognitive capacity to establish a system of communication and promote further recovery?”

Raanan Gillon, emeritus professor of medical ethics at Imperial College London, remarked on the study's significance, particularly as many view non-conscious states as potentially futile:

> “If there is a significant probability that the lack of consciousness is only apparent, as these studies suggest may be the case, it can be anticipated that more people would wish to be kept alive and be consulted about their wishes before decisions are taken to discontinue life-prolonging treatment.”

Gillon also raised ethical considerations regarding human rights and autonomy that require reevaluation in light of this research.

Erin Paquette, a pediatric critical care physician and bioethicist, pointed out the need for equitable access to EEG and fMRI technologies, noting:

> “If non-specialized centers don’t have access to these technologies, then patients in those centers may not have the same opportunities as others to change the course of their life.”

While both fMRI and EEG are powerful tools, Nicholas Schiff, a leading expert in neurological disorders of consciousness, believes that modern brain-computer interfaces (BCI) may offer new avenues for communication with individuals experiencing cognitive motor dissociation. He proposed:

> “Why not give them [BCI technology] to those with a disorder of consciousness to see if they can use it to communicate? At worst you get two weeks of useful data, at best you free them.”

Perspective Shift

Our focus has largely been on understanding the external world, but thanks to advancements in science and technology, we are now beginning to explore the intricate internal experiences of consciousness. The discovery of cognitive motor dissociation could transform our understanding of the brain, mind, and body connection.

This revelation may also reignite discussions around Dualism, the philosophical debate regarding the separation of mind and body. If cognitive motor dissociation exists, indicating that consciousness can be present despite a lack of physical response, it raises profound questions about the relationship between mental and physical states.

Ultimately, further exploration into these phenomena may yield significant insights, and only time will reveal the full implications of these findings.

This article was originally published in my newsletter, Curious Adventure, which highlights incredible discoveries across various scientific fields, reminding us of the vast unknowns that still exist.

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