New Consciousness Meter: How Do You Measure Consciousness In Coma And Brain Injury Patients?
Brain injury and coma patients greatly challenge their doctors because they present many uncertainties in terms of diagnosis and treatment. Illness or injury can wound a patient's brain, and it may be nearly impossible to tell how much damage has occurred ... and for how long it will last. Although a coma patient may be unable to move or respond to the environment, they are still alive and even maintain normal sleep patterns. Speech may be lost to them, yet if they continue to breath, their brains have retained non-cognitive functions.
Now, researchers from Italy, Belgium, Brazil, and the U.S. have proposed a new, more objective measure to judge a coma patient’s awareness and it’s based on the brain’s response to magnetic stimulation: a "consciousness meter."
The Science of Awareness
According to the New England Journal of Medicine, “the term ‘persistent vegetative state’ was coined by Jennett and Plum in 1972 to describe the condition of patients with severe brain damage in whom coma has progressed to a state of wakefulness without detectable awareness.” Previously, 'locked-in syndrome' had been coined by Plum and Posner in 1966 (though Alexandre Dumas created a fictional character with the condition in The Count of Monte-Christo over a hundred years before that, the International Encyclopedia of Rehabilitation notes). The need, then, to distinguish among patients with prolonged unconsciousness has been felt and addressed in the past and over time, but the old definitions have turned stale.
“Detecting consciousness may rely not only on a subject’s ability to communicate with the external environment, but also on the brain’s capacity for internal communication (effective connectivity),” Marcello Massimini, PhD, professor in neurophysiology, and one of the lead researchers on the recent study, wrote for the INCF Neuroinformatics Congress 2011.
Based on this root understanding of consciousness, Massimini and his colleagues worked to develop an objective scale of the level of consciousness, and a way to accurately measure it.
The Magnetic Consciousness Meter
The result is called the perturbational complexity index (PCI). The PCI is calculated by registering and recording the brain’s response to transcranial magnetic stimulation (TMS) and then analyzing the patterns created. In practical terms, a doctor would place some kind of magnetic device to the skull, generate a pulse, and track the brain’s “echo” or response. After recording the activity with an electroencephalography, they calculate a numerical score between 0 and 1 based on the complexity of the brain’s response. For instance, when the pulse causes neurons distributed across the brain to work together yet fire individually and uniquely, this would indicate a high functioning brain.
To establish this precise index of awareness, the researchers tested the method on a population of healthy subjects during different states of consciousness: wakefulness, dreaming, nonrapid eye movement sleep, and under different levels of anesthia (midazolam, xenon, and propofol). They compared these results with those obtained from patients who had emerged from coma (vegetative state, minimally conscious state, and locked-in syndrome).
“PCI reliably discriminated the level of consciousness in single individuals during wakefulness, sleep, and anesthesia, as well as in patients who had emerged from coma and recovered a minimal level of consciousness,” the authors wrote.
Can The Meter Reliably Measure Consciousness?
Their study, published this week in Science Translational Medicine, is only the beginning. The results must now be tested more extensively and replicated among a larger population of participants in order to be one day used as a reliable standard for registering consciousness in coma patients.
“Consciousness can grow and shrink," Massimini told ABC News. Most anyone who has alternated between daydreaming and solving math problems would agree. Precisely calibrating a person’s awareness, then, must be a complex and difficult yet ever-so-worthy task.
Sources: Casali AG, Gosseries O, Rosanova M, Boly M, Sarasso S, Massimini M, et al. A Theoretically Based Index of Consciousness Independent of Sensory Processing and Behavior. Science Translational Medicine. 2013.
The Multi-Society Task Force on PVS. Medical Aspects of the Persistent Vegetative State. New England Journal of Medicine. 1994.