August 22nd, 2013 by Michael Ricciardi
While our best brain theorists and cognitive philosophers still debate the exact nature of (and “threshold” for) consciousness, this same disagreement drives the need to define consciousness by doctors and neuroscientists treating or studying brain-damaged patients. New research out of the University of Milan using a brain stimulation technique has derived an ‘index’ for measuring the degree of consciousness present in a brain-injured person.
What is ‘Consciousness’ in a Brain-damaged Person?
A brain-traumatized patient may enter a “vegetative” stated (believed to be “minimally conscious”) or may be in a type of coma (in which varying degrees of conscious activity are present), or, even a ‘locked in” state in which the person is highly conscious, but simply can not move his/her body or speak. But these descriptive states of consciousness are based upon a combination of observations and imperfect EEG measurements and don’t give a highly accurate picture of brain activity. “Consciousness” is often a slippery, nebulous thing to define.
Because of this, scientists who study the brain are always seeking newer and better ways to peer inside the brain. This search has involved various brain-imaging technologies and mappings of neural dynamics to gauge the level of brain activity present, so that they may more accurately monitor, and thus ultimately define, this state we call consciousness. The problem with these approaches is that they begin with an implicit definition of consciousness, or a conscious brain, as being an “integrated brain” in which multiple networks of neurons fire relatively in unison to form a “cohesive pattern”.
But such a cohesive pattern is present when we dream, and neuroscientists do not define this state as “conscious” (when we start to become conscious in a dream state, we are on the verge of waking, of returning to consciousness). Thus it is an unreliable gauge of consciousness.
A New Method to Measure Conscious Brain Activity
Recently, Marcello Massimini and a team of neuro-physiologists at the University of Milan in Italy developed a new approach using magnetic stimulation to assess a person’s awareness. Data produced by this technique was then converted into a numerical “score” that the researchers call an ‘index of consciousness’. More specifically, it is called the perturbational complexity index (PCI).
In a conscious brain, there is wide-spread, coordinated neural network activity, but at the same time, these various neural groups can activate/fire independently, generating their own unique patterns of activity. Separating out components of this dynamic state — finding the “information-rich” activity — is what makes measuring consciousness so tricky; it requires discerning both widely-distributed neural activity and individualized neural activity at the same time.
Marcello Massimini and colleagues began exploring a way to more precisely calculate this state of mind (brain) and hit upon using a technique known as transcranial magnetic stimulation (TMS) to “perturb” (hence the name of the index) the brain’s numerous networks of neurons. In TMS, a magnetic coil that generates magnetic pulses is placed next to the surface of the skull. The pulses provoke a response from these neurons that reverberates throughout the brain.
At that point, the researchers record this “echo” of the perturbed brain activity using an EEG (electroencephalograph) machine. The combined brain wave patterns are then converted into a mathematical value and given a score between 0 and 1.
If the 9electrical) response to the TMS pulses was “information-rich” (i.e., showing both neural network activity spread out over the whole brain and also individual network activity), then these responses received higher scores. If widely-separated groups of neurons fire together (in a synchronized fashion), they are viewed as signs of less conscious activity, and the PCI equation “compresses” them (reduces their value) and so they carry less weight for the overall PCI score.
“The less we can compress the pattern, the more information is in it,” Massimini explains. [source, see link below]
And the more information-rich, the higher the score, and that means a greater likelihood of a conscious brain, of the presence of true consciousness.
To calibrate their scoring system/approach, the team first applied the technique to groups of healthy, awake subjects to establish a reference for normal conscious activity. Then, they used the technique on subjects who were in deep sleep or under anesthesia to establish a reference for unconsciousness. They found no overlap between the conscious and unconscious subjects’ scores which was useful in deciding on a “cut-off” point, or threshold, for consciousness (note: this was determined to be somewhere between the lowest conscious score [0.44] and the highest unconscious score [0.31].
Finally, the technique was used on 20 patients who were suffering from some form of brain trauma.
Convincingly, those described as being in a vegetative state (“awake, but wholly unconscious”) received very low scores ranging from 0.19 to 0.31. Those patients who had recently emerged from a coma showing typically varying levels of brain activity received intermediate scores. What’s more, those that were in a locked-in state (just two of the subjects) received high PCI scores of 0.51 and 0.62 (as high as healthy, awake subjects) — reflecting normal cognitive abilities, despite their inability to move (note: these subject, being able to perceive and process information around them, were able to move their eyes to communicate).
The research offers a compelling proof of principle; without any interaction from the subjects, and looking only at the converted TMS > EEG > PCI data, the team was able to precisely index subjects’ states of consciousness, placing them on a ‘consciousness continuum”.
An ‘Index’ or A ‘Signature’ of Consciousness?
Previous research on brain-traumatized subjects (as reported here on Planetsave, July, 2011) using EEG technology found a “signature of consciousness” that involved a key feedback loop between the frontal lobes of the neocortex and a deeper brain region called the thalamus. Patients lacking this signature were deemed non-conscious or only “minimally conscious.”*
Also, no doubt this newest study was able to pick up some of this “signature feedback activity” (noted, above) but whether or not it was separately identified and/or defined as “individualized” is not clear. It would be interesting to compare these two approaches to gauging conscious awareness, to see if they “mesh”, or compliment each other, perhaps yielding an even more precise gauge of this slippery thing called consciousness. Since nearly 40% of those deemed “minimally conscious” eventually wake up, making such assessments more precise is paramount.
These most recent results will not be declared truly definitive until they can be replicated with much larger groups.
The research was published in the Aug. 14, 2013 edition of the journal Science Translational Medicine.
*Interestingly, the U of Milan team did find some slight overlap in the range of score for those subjects deemed in a “minimally conscious state” (who showed sporadic signs of awareness like following a simple command) and those who had recently emerged from from this minimally conscious state (who showed limited ability to communicate). This represents a grey area in consciousness and shows again how tricky any definitive assessment (in brain-damaged patients) can be.
Some source material (including quote, image) for this post came from the Science NOW article ‘A Magnetic Trick to Define Consciousness’ by Kelly Servick
Top Photo: (credit: Adenauer G. Casali) University of Milan scientists use a magnetic stimulation technique to trigger an EEG response in a brain-injured patient; the echo of this brain event will be scored so as to ‘index’ her state of consciousness.
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