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. Making electrical echoes in the brain 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.

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. Bedside test of consciousness for intensive care? 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: "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." 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.