Between Theory and Clinic: The Contribution of Neuroimaging in the Field of Consciousness Disorders

The amount of patients surviving severe brain injury has gradually increased over these last decades thanks to the development of intensive care. These patients either recover quickly from coma or go through prolonged disorders of consciousness such as vegetative state/unresponsive wakefulness syndrome (VS/UWS) or minimally conscious state (MCS). While patients in a minimally conscious state are to some extent aware of themselves and the environment, and show fluctuating but reproducible signs of consciousness, patients in a vegetative state/unresponsive wakefulness syndrome are awake but only show reflexive behaviors. These patients are unable to communicate and present vigilance fluctuation, sensory deficits as well as severe motor and language impairments. Even though behavioral assessment currently remains the gold standard for diagnosis, a number of studies highlights the difficulty in making the distinction between conscious and unconscious patients based on clinical examinations and show a misdiagnosis rate as high as 40%. Misdiagnosis can nevertheless have serious consequences on patient’s management, medically but also ethically (i.e., regarding end-of-life decision). The emergence of functional neuroimaging techniques (such as positron emission tomography – PET and functional magnetic resonance imaging – fMRI) opened new opportunities to study brain activity in patients with disorders of consciousness (DOC). Recent neuroimaging tools have brought new understandings on how the brain functions after coma, and how these tools can complement bedside assessment by improving diagnosis and prognosis of DOC patients. Indeed, we know now that most patients in VS/UWS present partial activation of sensory networks and impaired functional connectivity contrary to patients in MCS. The reemergence of thalamo-cortical connections has also been associated with recovery of consciousness; whereas, thalamic atrophy has been associated to chronic DOC. Recent findings have also stressed the interest of neuroimaging in the management and the treatment of these patients. fMRI has been used as brain computer interfaces to detect consciousness in unresponsive patients and to allow basic communication in minimally conscious patients. Neuroimaging techniques are also currently being used to examine the effects of potential therapy such as pharmacological medications (e.g., Amantadine or Zolpidem) and brain stimulations (e.g., transcranial direct current stimulation or repetitive transcranial magnetic stimulation).