Functional MRI can help to assess the level of consciousness of patients in the « vegetative » unresponsive or minimally conscious states.
After a severe traumatic or anoxic brain injury, distinction between coma, vegetative state (now called unresponsive wakefuless syndrome) and minimally conscious state (states generally called « disorders of consciousness ») is a complex challenge for the neurologist (Schnakers et al 2009). The limits which separates these states, and even the definition of "consciousness" remain challenging. Some behavioral tests can help in the differential diagnosis and differentiation from locked-in syndrome, but often these are impaired by many confounding factors.
Minimally conscious state (MCS), which refers to patients with severe brain damage but who demonstrate unequivocal, but intermittent, behavioral evidence of awareness of self or their environment and hence possible pain perception (Boly et al 2008), is the most pressing to study with functional MRI. Identifying any form of consciousness can have great medical, psychological and ethical impact on the patient’s care and management.
Functional MRI has the power to detect brain activation elicited by a stimulus, even in the absence of patient output. It can therefore be used as a marker of brain activity or even "consciousness" in patients in a « vegetative » or minimally conscious state. Laureys (2004) and Schiff (2005) et al. found high-level cortical activations in MCS induced by emotionally meaningfull auditory stimuli. It suggested that some MCS patients may retain widely distributed cortical systems with potential for cognitive and sensory function despite their inability to follow simple instructions or communicate reliably.
The teams led by Owen (Cambridge) and Laureys (Liège) applied a more complex paradigm to further investigate the state of consciousness of a patient who was thought to be in a « vegetative state ». The patient was asked to perform 2 mental imagery tasks: tennis playing versus walking in a her house. Brain activations observed were identical to the ones obtained in healthy volunteers: supplementary motor area (SMA) while mentally playing tennis ; parahippocampal gyrus, posterior parietal cortex, and lateral premotor cortex while visiting her house (Owen et al 2006). Out of the 54 patients enrolled in a study performed by the same groups (Monti, Vanhaudenhuyse et al. 2010), 5 were able to willfully modulate their brain activity. One patient, without any form of communication at the bedside, was able to modulate his brain activity (tennis playing versus walking in his house) to answer "yes" or "no" to questions during the functional MRI examination. This method could be used to create a basic interaction with these patient, allowing them to answer simple binary questions (about pain, living will, etc.).
Resting-state fMRI, i.e. functional MRI without any stimulus, has also been used to assess patients with disorders of consciousness. The default network is defined as a number of areas including the precuneus, bilateral temporo-parietal junctions and medial prefrontal cortex, which are more active at rest than when the subjects are involved in an attention-demanding cognitive task. Vanhaudenhuyse et al. 2009 has showed that the connectivity of this default network is decreased in severely brain-damaged patients, in proportion to their degree of consciousness impairment.
Would you like to further discuss the implementation of these methods at your hospital, please contact us.
More information: Coma Science Group, Liege University, Belgium.
By Dr. Laurent Hermoye & Pr. Steven Laureys
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