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The Challenge of Determining Consciousness

cschoonover's picture

Consciousness is a state of awareness of self and the environment and is determined by the level and content of this awareness, also referred to as arousal and awareness respectively (1). Consciousness itself takes many forms, as can be seen in the many combinations of level and content of awareness. When describing comas and vegetative states, people often use the terms interchangeably and freely without regard for the differences in consciousness of patients in these states. This however does not account for the differences in consciousness of patients in these states. In a coma, a patient is described as having “disordered arousal,” as opposed to an impairment of the content of consciousness (as is found in patients in minimally conscious states). The complete absence of all the content of consciousness is what characterizes a vegetative state (1).

Both comas and vegetative states can arise from similar causes, such as traumatic brain injury and the recovery from coma may lead to a vegetative state. While the causes of coma and vegetative state can be very much the same, the behaviors vary. Coma is characterized by a failure of the eyes to open in response to stimulation, motor responses only to nerve stimulation (reflexes), and only simple vocalizations of “nonword” sounds (6). Coma is a transient state and thus patients who survive begin to wake up after approximately two weeks, assuming no complications arise. Some of these patients will recover quickly, but others recover over long periods of time. The first stage of this long recovery may be a vegetative state. Patients typically present with grimaces, an emotional-limbic reflexive expression, not an indication of discomfort (4). This state is further described by a limited recovery of the level of awareness, determined by alternating periods of “eyes-open” and “eyes-closed” states. A patient who remains in this state for longer than 30 days is said to be in a persistent vegetative state (4).

With continual development of technologies and research methods, the definition of consciousness as it relates to coma and vegetative state is in flux. A recent study in Belgium reported that five people who had been in vegetative states were did in fact exhibit brain activity. In this study, which utilized the imaging capabilities of MRI’s, patients were asked to associate the answer “yes” with thinking of playing tennis, and “no” with thinking of being in one’s home (2). The different thoughts activate different areas of the brain: the motor cortex when thinking of playing tennis, and the spatial areas when thinking of being in one’s home. The activation of these areas is detected by MRI scans. This brain activity is suggestive of consciousness, but it is not clear what kind of consciousness, or where on the continuum of consciousness these patients are (2). In contrast, many severely injured patients described as minimally conscious (able to intermittently respond to commands) did not show any significant activity in brain scans. This raises the question of who is more conscious: those that did show evidence of activity or those that did not, despite the fact that those who had a lack of brain activity were clinically characterized as having a higher level of brain functioning.

In another study, researchers discovered that “some brain regions consistently become less active during task performance and more active when people are resting quietly…a circuit now known as the default mode network (DMN)” (5). The activity of this region may represent conscious thought, an idea tested by observing people in deep sleep. Using a specialized MRI scan and EEG, the researchers determined that, over the course of wakefulness to deep sleep, the functional connections in the DMN change: some parts of the DMN become more synchronous with each other while others fell out of synchronicity. This demonstrated that the DMN changes as the level of consciousness changes, which proves it to be a window into consciousness. The DMN also broaches the idea and nature of “self,” in that these circuits seem to be active when a person is engaged in more introspective activities, a form of self-consciousness (5).

The “I-function” box may be helpful in considering the neurological underpinnings of the consciousness of the “self.” The I-function is the “me” box, which is a conceptual way of describing self-consciousness based on particular brain structures. These brain structures are a part of the nervous system that is experienced only by one’s self, independent of the outside environment. The I-functions is further defined as the restrictive perception of one’s actions and behaviors. In clinical evaluations, it is difficult to accurately support a diagnosis using the I-function box because it is not always clear if it is active. Recent research suggests that patients in vegetative states could have an active I-function box. Further research is needed to determine whether the I-function could play a role in the evolution of new diagnostic tools for discriminating levels of consciousness and thus improving the diagnosis of disrupted states of consciousness.

The studies provide useful information for refining the diagnosis of patients with “disorders of consciousness” (3). It is difficult to objectively assess behaviors of these patients because motor responses are variable and many types of stimuli can induce seemingly autonomic responses from the brain. The ability to elicit neural responses that depend on “time-dependent and sustained responses generated by the patient,” provides the possibility of “reportable awareness,” but raises the question of whether this should be a form of communication (3).

These studies force us to question the definition of “consciousness” as it relates to coma and vegetative state. The working definitions of each of these states may, in the future, have to be altered to accommodate the recent discoveries of brain activity as shown by brain imaging, which may reflect consciousness. It is for this reason that it is vital for the public, doctors, researchers, etc. to recognize that it can be challenging to determine which of these states a patient is in. The studies demonstrate the variability in the degree of awareness among patients with disorders of consciousness. Modern technology is in the process of challenging the way we diagnose patients and thus where on the continuum of consciousness they fall. Furthermore, it may help to define the lines between vegetative state and minimally conscious state. If these lines were clear, the prognoses may change. Considering this, it is imperative to recognize the importance of the use of the correct terms when describing a patient with altered consciousness. But it is also important to respect the idea that this is a field in which the research methods and technologies are transforming the definitions and the diagnosis of patients with disrupted awareness.


1. Bateman, David E. "Neurological Assessment of Coma." Journal of Neurology, Neurosurgery, and Psychiatry 71 (2007):     i13-i17. PubMed. Web. 18 Feb. 2010. <>.

2. Carey, Benedict. "The Riddle of Consiousness." The New York Times. N.p., 5 Feb. 2010. Web. 16 Feb. 2010. <>.

3. Owen, Adrian M, Nicholas D Schiff, and Steven Laureys. "A New Era of Coma and Consciousness Science." Progress in Brain Research 177 (2009): 399-411. ScienceDirect. Web. 17 Feb. 2010. <>.

4. Schiff, N D. "Coma and other Pathological Disorders of Consciousness." Encyclopedia of Neuroscience (2008): 1143-1147. ScienceDirect. Web. 17 Feb. 2010. <>.

5. Stimson, Daniel. "The Sleeping Brain Yields Clues to the Conscious Mind." National Institute of Neurological Disorders and Stroke. N.p., 27 July 2009. Web. 16 Feb.2010. <    ep_sleep.htm/>.

6. Young, G. Bryan. "Coma." Annals of the New York Academy of Sciences 1157 (Mar. 2009): 32-47. Wiley InterScience. Web. 18 Feb. 2010. <>.


Paul Grobstein's picture

clues to consciousness?

"it is also important to respect the idea that this is a field in which the research methods and technologies are transforming the definitions ..."

Perhaps this is actually the most significant thing that will in the long run come from contemporary observations?  See Discovering awareness in vegetative state patients and my comments following it.