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

- Preliminary data exist for the presence of pain perception in some Unresponsive Wakefulness Syndrome (UWS) patients.
- Pain-induced γ-oscillations within limbic system are related with pain perception in disorder of consciousness patients.
- Limbic system activation was preserved in some UWS patients, suggesting that they perceive the affective component of pain.

ObjectiveAlthough 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.MethodsTo 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 γ-band LORETA activations and the ERP γ-power magnitude induced by laser stimulation, as well as the heart rate variability (HRV).ResultsWe found partially preserved cortical activations and ERP γ-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.ConclusionsSome UWS patients may somehow perceive the affective components of nociceptive stimulation.SignificanceThe diagnosis of functional locked-in syndrome should be taken into account when dealing with DOC differential diagnosis.