New methods of measuring awareness could help doctors better treat these patients and better predict the likelihood of recovery and give families an indication on whether their loved one is aware of their presence. A Belgian study describes this week in the journal Science a new “consciousness test”. The team from the University of Liège measured the electrical response to auditory stimulation by means of “high-density” electroencephalography (EEG). Using a sophisticated mathematical model, researchers identified a neural signature of consciousness in healthy volunteers and in patients with “minimal consciousness” but not in unresponsive so-called “vegetative” patients. The study helps unravel one of science greatest mysteries : how subjective consciousness arises from the physical activity of trillions of brain connections (2).
Research directed by Dr Mélanie Boly and Pr Steven Laureys of the Coma Science Group (Cyclotron Research Center and Neurology Department of the University and University Hospital of Liège) gathered EEG recordings in 22 healthy volunteers and 21 patients with severe brain damage. Eight patients were “vegetative” (that is, non-responsive wakefulness, characterized by the presence of eye opening only accompanied by reflexive body movements) and 13 were “minimally conscious”, a condition in which patients sometimes show deliberate movements such as eye-tracking of a person or orientation of painful stimuli.
The researchers made EEG measurements while subjects listened to a series of simple tones. Previous studies had shown that the brain’s electrical response changes when the frequency of the tones changes. These brain responses disappear during sleep and under anesthesia, suggesting that this may be an indicator of consciousness. Dr Mélanie Boly and colleagues found that unconscious “vegetative” patients showed only a transient response of less than one tenth of one second.
In collaboration with neuroscientist Karl Friston and his team at the University College London, mathematical models were developed to identify the activated cerebral network and identify its “consciousness connections”. Previous studies of the Liege team had already shown a widespread “consciousness network” encompassing the fronto-parietal gray matter and pointed to the crucial role of this network’s connectivity or communication. “This new study suggests that this network’s feedback loops, or ‘top-down’ connections, are necessary for conscious experience”, said Dr Mélanie Boly. Professor Steven Laureys stressed : “This is just the beginning, current studies are examining the prognostic value of this new technique.”
See the video
www.ulg.ac.be/webtv/testconscience (available after embargo-lift time)
More than 250 sensors measure the electrical response of the brain to auditory stimuli in coma patients and allow physicians to detect signs of consciousness.
© comascience.org ULg
Auditory stimulation activates the auditory cortex (in red) in “primary” (1) and “associative” (2) areas, but conscious perception depends on the involvement of a widespread frontoparietal network (in blue). The new study shows that top-down feedback connections from the latter to the former are crucial for the emergence of consciousness. This backward connectivity loop (blue arrow) is preserved in patients in “minimally conscious state” but not in unconscious “vegetative” patients. © comascience.org Ulg
(1) “Willful modulation of brain activity in disorders of consciousnesss”, Vanhaudenhuyse Monti MM & A, Coleman MR, Boly M, Pickard JD, Tshibanda JF, Owen AM, Laureys S, New England Journal of Medicine (2010) 362 (7) :579-89. Read also “An improbable dialogue” on Reflexions’s website of the University of Liege.
(2) The article “Preserved feedforward but impaired top-down processes in the vegetative state” Boly M, Garrido MI, Gosseries O, Bruno MA, Boveroux P Schnakers C, Massimini M, Litvak V, Laureys S, Friston K, has been published in Science 13 May 2011.
Note for the Editors
A patient in a “vegetative state” shows only reflex movements. If she/he is showing more than mere reflexes but cannot communicate, the patient is described as being in a “minimally conscious state”. A patient in a vegetative state has a worse prognosis than a patient in a minimally conscious state. Making the correct diagnosis is important not only for end-of-life decisions, but also for rehabilitation and pain treatment. Indeed, the team of the University of Liege has previously shown that patients in a minimally conscious state perceive pain (M. Boly et al. Lancet Neurology, 2008) and experience emotions (S. Laureys, Neurology, 2004).
These studies are the result of a collaboration between the teams of Liege, London (Professor K. Friston, M. Garrido and Dr V. Litvak) and Milan (Pr M. Massimini, ULg visiting professor). The multidisciplinary team (Neurology, Anesthesia, Intensive Care, Neuroradiology, Neurosurgery, Psychology, Medicine and Rehabilitation in collaboration with engineers and physicists and guest lecturers from across Europe) of the Coma Science Group aim to improve medical care and scientific understanding of disorders of consciousness encountered after severe brain damage such as coma, “vegetative”, minimally conscious and locked-in states. Patients from all over Europe come to Liege for a brief hospitalization, with the aim to better document the diagnosis, prognosis and therapeutic options.
The Coma Science Group is funded by the Belgian National Fund for Scientific Research (FNRS), European Commission (Decoder, Mind Bridge, Discos COST & Projects), Ministry of Health and US Mind Science, James S. McDonnell and Léon Fredericq Foundations. http://www.coma.ulg.ac.be
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