Humans are conscious during their waking hours, and unconscious during sleep. Doctors typically determine whether or not a person is conscious by giving them verbal commands and testing whether they respond (such as the command: “squeeze my hand”). However, this method is incomplete because sometimes the brain is, in fact, conscious, but is unable to respond to verbal cues for one reason or another. One good example of this is people who are able to hear their loved ones speak to them while in a coma, but are unable to respond in any way. One reason that this might occur is that different complexes of neurons in the brain are responsible for hearing, processing and carrying out commands. Varying levels of participation occur during different levels of consciousness. For example, the brain may hear someone speaking while asleep, but is unable to associate emotions or responses with the words that are said.
New research, led by Dr. Marcello Massimini at the University of Milan in Italy, proposes a unique test for consciousness called the Perterbational Complexity Index, or PCI. The method involves using strong magnetic stimulation to “shake” the brain and then recording the action of the neurons. By doing so, scientists are able to judge how much information is being processed as a whole.
To test the method, Massimini and his team examined the impacts of the new technique on patients with brain injuries, patients under anesthesia and patients in a deep sleep. The PCI was able to measure the level of brain consciousness in each of the three types of patients. The research suggested that the complexity of brain response was closely linked to the level of consciousness in the patient.
The new research provides valuable information that can be used to help monitor patients’ brain activity, particularly those with severe injury. The team cautions, however, not to use the test as a sole judge of consciousness when examining patients in a vegetative state. Rather, the team suggests using the PCI to help monitor patients and test for day-to-day improvements in brain response. The test can also be used to help determine whether the patient is thinking or feeling anything, Live Science explains. Massimini plans to further expand the study to more patients in order to better define the PCI index.