Perhaps the most interesting conundrum of neuroscience is the nature of human consciousness. How does the three-pound mass of spongy brain tissue composed of approximately 100 billion neurons drive all aspects of the conscious mind, from emotions to creativity?
We often perceive ourselves or others as “conscious” if we are able to detect and respond to changes in the surroundings. However, those who experience severe brain disorders or traumatic injuries may fall into a persistent vegetative state, a condition during which an individual is alive but unable to react to the environment. Although vegetative patients are widely deemed to be in a deep state of unconsciousness, our ability to learn about the conscious experience of others largely depends on the capacity for communication. If an individual is fully aware of his or her surroundings, yet have lost the ability produce any overt physical response, can doctors really diagnose that person as unconscious? Are vegetative patients truly unconscious as physicians often diagnose them to be, or are they simply trapped inside their own bodies without the ability to communicate their conscious experiences?
Recently published in Proceedings of the National Academy of Sciences, a new study by Lorina Naci and colleagues at the University of Western Ontario showed that a 35-year-old vegetative man was able to respond to a Hitchcock movie, illustrating an unexpected level of consciousness for an unresponsive individual.
Initially, the authors of the study subjected 12 healthy volunteers to watch the thriller movie inside a functional magnetic resonance imaging (fMRI) machine, which measures brain activity by analyzing the flow of oxygenated blood. As the movie progressed, activity levels in the frontal and parietal regions of the volunteers’ brains oscillated. At identical points in the film, similar brain activity patterns were observed throughout the volunteers. Additionally, the study also investigated another group of healthy volunteers who watched a scrambled version of the film in which no identifiable plot could be followed. By comparing and analyzing the fMRI data obtained from the two groups, the authors of the study were able to deduce which pattern of brain activity corresponded with the ability to follow the plot of a movie, a higher-order cognitive ability that requires a greater degree of consciousness than just merely watching a movie without paying any attention. In other words, the brain regions that were activated were implied to be physical substrates of a specific conscious experience induced by watching and following a thriller movie.
Astonishingly, these patterns of activity measured by the fMRI scanner were also active in a clinically diagnosed vegetative man when he was shown the Hitchcock movie. Concluded to be in a vegetative state 16 years ago following a horrific fight, the 35-year-old man exhibited the same brain activities as those of healthy individuals while they watched the movie, suggesting that he may be conscious enough to follow the plot of the film.
This study is not the first to question the reliability of clinically assessing whether or not an individual is in a vegetative state. For example, previous reports have also used fMRI and other tools to detect neuronal substrates of consciousness in vegetative patients, providing evidence for the possibility that a significant population of consciously aware patients are misdiagnosed as vegetative. These findings emphasize a significant clinical and ethical need to establish a method to detect consciousness in patients who maintain a level of awareness but are misdiagnosed as vegetative based on classical behavioral assessments. This present study demonstrates a novel methodology to measure and quantify consciousness in both healthy individuals and vegetative patients who lack behavioral response. In the future, physicians may rely on similar neuroimaging techniques to improve clinical assessment of unconsciousness, allowing for better treatment of patients who are aware but lack behavioral responses.
