Pain perception in patients with chronic disorders of consciousness: What can limbic system tell us?

Objective: Although it is believed that patients with Unresponsive Wakefulness Syndrome (UWS) do not feel pain, recent neuroimaging and neurophysiologic studies have demonstrated some residual traces of nociceptive processing. Methods: To confirm this growing evidence, we evaluated 21 patients suffering from chronic disorders of consciousness (DOC) ( both UWS, n = 11, and Minimally Conscious State - MCS -, n = 10), using an Event-Related Potential (ERP) Low-Resolution Brain Electromagnetic Tomography (LORETA) approach, based on nociceptive repeated laser stimulation (RLS). We delivered laser stimuli to the dorsum of both hands and analysed the gamma-band LORETA activations and the ERP gamma-power magnitude induced by laser stimulation, as well as the heart rate variability (HRV). Results: We found partially preserved cortical activations and ERP gamma-power magnitude in all MCS and two UWS individuals. These effects were paralleled by a purposeful behaviour, and a reduced HRV concerning nociceptive stimulation, whereas the two UWS individuals showed no more than reflex behaviours, besides a strong limbic activation. Conclusions: Some UWS patients may somehow perceive the affective components of nociceptive stimulation. Significance: The diagnosis of functional locked-in syndrome should be taken into account when dealing with DOC differential diagnosis. (C) 2017 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.