Even though functional MRI (fMRI) studies have demonstrated that some patients thought to be in a vegetative state are consciously aware, the use of fMRI in most of these individuals is prevented because of cost issues and accessibility.
Patients also incur significant physical stress during transfers to suitably equipped fMRI facilities. Imaging datasets often show objects of movement from patients unable to remain still, and fMRI scans cannot be performed on individuals with metal implants, such as pins and plates, which are common in people who sustained a trauma-injury.
Professor Adrian M Owen, Dr. Damian Cruse and team set out to determine how effective a portable EEG device might be in detecting awareness in patients who were in a vegetative state.
The researchers examined 16 patients at 2 European centers at the Addenbrooke's Hospital in Cambridge, UK and at the University Hospital of Liege in Belgium. Each patient had been officially diagnosed using relevant criteria as being in a vegetative state sustained either through traumatic brain injury (5) or non-traumatic brain injury (11). By using a novel approach to detect awareness in patients lacking any physical ability to respond, patients were asked to imagine movements of their right-hand and toes.
When researchers examined the 16 patients diagnosed in the vegetative state together with 12 healthy controls, they discovered that three out of sixteen patients (19%) were able to repeatedly and reliably generate appropriate EEG responses to two distinct commands despite being behaviorally entirely unresponsive.
Two of the patients had sustained a traumatic brain injury whilst the other individual had a non-traumatic brain injury. There was no significant link between patients' clinical histories, such as age, time since injury, cause, and behavioral score, and their ability to follow commands.
The researchers explain and conclude:
"Our findings show that this EEG method can identify covert awareness in patients diagnosed in the vegetative state with a similar degree of accuracy to other methods of detection; it is a considerably cheaper and more portable bedside technique...this method could reach all vegetative patients and fundamentally change their bedside assessment.
The degrees of freedom provided by EEG could take this technique beyond binary responses to allow methods of communication that are far more functionally expressive, based on many forms of mental state classification.
The development of techniques for the real-time classification of these forms of mental imagery will enable routine two-way communication with some of these patients, allowing them to share information about their inner worlds, experiences, and needs."
Professor Morten Overgaard at the Cognitive Neuroscience Research Unit (CNRU) in Aalborg and Aarhus University, Denmark, and Rikke Overgaard at the CNRU Centre of Functionally Integrative Neuroscience and MindLab, Aarhus University, Denmark, say in a linked Comment:
"A new classification system is necessary if the goal is to understand the cognitive functioning of patients in the vegetative or minimally conscious states. Such a system should begin with a much more explicit attempt to use objective methods that have been correlated with reports of subjective experience in healthy individuals."