How Can Science Explain Consciousness? Lessons from Coma and Severe Brain Injury
Steven Laureys, Coma Science Group, GIGA-Research, University and University Hospitalof Liège, Belgium
http://www.coma.ulg.ac.be
The past 15 years have provided an unprecedented collection of discoveries that bear upon ourscientific understanding of recovery of consciousness in the human brain following severe brain
damage. Highlighted among these discoveries are unique demonstrations that patients with little or no
behavioral evidence of conscious awareness may retain critical cognitive capacities and the firstscientific demonstrations that some patients, with severely injured brains and very longstanding
conditions of limited behavioral responsiveness, may nonetheless harbor latent capacities for recovery.
Included among such capacities are particularly human functions of language and higher-levelcognition that either spontaneously or through direct interventions may reemerge even at long timeintervals or remain unrecognized.
When patients in “persistent vegetative state” (recently also coined unresponsive wakefulness
syndrome) show minimal signs of consciousness but are unable to reliably communicate the term
minimally responsive or minimally conscious state (MCS) is used. MCS was recently subcategorizedbased on the complexity of patients' behaviors: MCS+ describes high-level behavioral responses (i.e.,command following, intelligible verbalizations or non-functional communication) and MCS- describes
low-level behavioral responses (i.e., visual pursuit, localization of noxious stimulation or contingent
behavior such as appropriate smiling or crying to emotional stimuli). Patients who show nonbehavioral evidence of consciousness or communication only measurable via ancillary testing (i.e.,functional MRI, positron emission tomography, EEG or evoked potentials) can be considered to be ina functional locked-in syndrome.
An improved assessment of brain function in coma and related states is not only changing
nosology and medical care but also offers a better-documented diagnosis and prognosis and helps tofurther identify the neural correlates of human consciousness. Taken together, recent studies show thatawareness is an emergent property of the collective behavior of frontoparietal top-down connectivity.
Within this network, external (sensory) awareness depends on lateral prefrontal/parietal cortices whileinternal (self) awareness correlates with precuneal/mesiofrontal midline activity. Of clinicalimportance, this knowledge now permits to improve the diagnosis, prognosis and treatment of patientswith disorders of consciousness, which currently remains very challenging. New technologicaladvances now also permit to show command-specific changes in fMRI, EEG or eye-pupil
measurements providing motor-independent evidence of conscious thoughts and in come cases even ofcommunication. We will conclude by discussing related ethical issues and the challenge of improving
our clinical care and quality of life in these challenging patients with disorders of consciousness.

References- Diagnostic precision of PET imaging and functional MRI in disorders of consciousness: aclinical validation study Lancet (2014) Apr 15- Consciousness and complexity: from theory to practice Science Translational Medicine(2013) Aug 15- Disorders of consciousness: responding to requests for novel diagnostic and therapeuticinterventions Lancet Neurology (2012) 11:732-738- Bedside detection of awareness in the vegetative state Lancet (2011) (9809) 2088-94- Preserved feedforward but impaired top-down processes in the vegetative state Science(2011) 858-862- Willful modulation of brain activity in disorders of consciousness New England Journal ofMedicine (2010) 579-89- The neural correlate of (un)awareness: lessons from the vegetative state Trends Cogn Sci(2005) 556-91