Main Category: Neurology / Neuroscience
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Article Date: 15 Aug 2013 - 8:00 PDT Current ratings for:
Brain injuries: measuring consciousness by 'perturbing the brain'
Assessing consciousness in patients with severe brain trauma is a difficult challenge for doctors, as the injury effectively takes away any ability to blink, squeeze a hand or otherwise respond. But scientists have found a way to measure the brain's response to a magnetic pulse, helping them determine a person's level of awareness.
The researchers in Italy, led by Marcello Massimini, set out to find a reliable, objective way to distinguish an unconscious brain from a conscious one. Though many existing methods use brain imaging or electrical activity of neurons, Massimini says "that's not enough."
He notes that sometimes an unconscious brain can appear integrated, meaning groups of cells from different regions can activate to make a connected pattern.
Stimulating a sleeping person's brain, he says, can produce a wave of activity that "propagates like a ripple in water," even though the person is not conscious.
On the other side of the fence, the researchers say that around 40% of patients who are initially judged to be unresponsive are found later to possess a level of consciousness.
To measure consciousness, Massimini and his colleagues created the perturbational complexity index (PCI), which involves holding a magnetic coil to the skull and measuring the response. This transcranial magnetic stimulation (TMS) generates a pulse that sparks a response through the underlying neurons and propagates throughout the brain.
EEG readings were analyzed after pulsing unconscious brains with the magnetic coil.
By recording the brain's response by electroencephalography (EEG), the researchers then turned the information into a score between 0 and 1. The so-called information-rich responses - those distributed across the brain that are still individualized - receive higher scores, denoting a higher level of consciousness.
The researchers calibrated their system by using healthy patients in three different states: awake, deep sleep and under anesthesia, which served as a reference for unconsciousness.
For the healthy patients, they measured the highest unconscious score at 0.31 and the lowest conscious score at 0.44.
When they tested 20 people with brain damage who were believed to be in a state of partial wakefulness but who showed no signs of awareness, they observed low scores between 0.19 and 0.31.
Additionally, when Massimini and his team tested on two patients who had normal cognitive abilities (for example, they could shift their eyes) but were unable to move, they received PCI scores of 0.51 and 0.62, which rated at the same level as the healthy patients.
The researchers say that the index they have effectively created provides a scale of consciousness and unconsciousness that could be used as an "objective" test "at the bedside."
In an interview with Bloomberg, Marcello Massimini said:
A team from Belgium recently discovered a simple method for testing coma patients involving resistance to eye-opening, but the index from Massimini and his colleagues could provide a measurable indicator for diagnosing levels of consciousness. Written by Marie Ellis"It will be very important to perform measurements right in the ICU in the acute phase to have an objective marker of what's happening and to track improvements occurring spontaneously or brought about by treatment.
If you have a number, you can start working towards an evidence-based treatment."
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A Magnetic Trick to Define Consciousness Kelly Servick, Science, published online 14 August 2013.
A Theoretically Based Index of Consciousness Independent of Sensory Processing and Behavior Marcello Massimini, et al., Science Translational Medicine, published online 14 August 2013.
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posted by Mark on 15 Aug 2013 at 11:12 am
This is an interesting study and approach. A few questions come to mind:
1) when sending such a ping request to the brain in a conscious person, does the person feel such a magnetic pulse?
2) Did the researchers test said device on themselves first before attaching it to patients?
3) if such stimulus reports the person is not conscious, they could be sleeping, or truly in a coma state...would this test be used to determine whether a person lives or dies?
If question 3 becomes a fact, and it could potentially be used to determine whether to keep someone on life supporting equipment or not, then I would have to say I have some objections to said test. As much as we think we know about the brain, we still don't know enough, and the decisions of life and death are taken up by persons assuming certain facts.
We don't know enough about the conscious or unconscious states, and for all we know, a coma could be an altered sense of reality, in a dream like world, but for that person they are alive, and breathing, in their mind, but perhaps this test says they're conscious.
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posted by Kevin K on 15 Aug 2013 at 8:25 am
How can you be awake and unconscious at the same time?
"...20 people with brain damage who were believed to be awake but completely unconscious..."
Editor's note: Thank for your comment, Kevin. Marcello Massimini, (lead author of the study) reported, "those who were believed to be in a vegetative state - awake but completely unconscious - got very low scores (between 0.19 to 0.31)."
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