Shaping Thalamo-cortical Plasticity: A Marker of Cortical Pain Integration in Patients With Post-anoxic Unresponsive Wakefulness Syndrome?

Background The distinctive feature of unresponsive wakefulness syndrome (UWS) is the dissociation between arousal and awareness. Cortico-cortical and thalamo-cortical connectivity and plasticity play a key role in consciousness. UWS patients do not usually show any "cortical" behavioral sign in response to painful stimulation. Nevertheless a "focal conscious" pain perception has been hypothesized. Hypothesis Since defective plasticity and connectivity within pain matrix could be striking mechanisms of non-conscious pain perception and, consequently, of non-cortical responses in UWS subjects, aim of our study was to investigate pain-motor plasticity in such patients through a specific paired laser associative stimulation protocol (L-PAS). Methods We enrolled 10 post-anoxic subjects and 10 healthy controls evaluating clinical and electrophysiological parameters before and after the application of such protocol. Results Some patient showed a restored pain-motor integration with a partial motor cortex excitability modification. Conclusions Although we studied a small cohort of post-anoxic UWS patients and the results obtained were short-lasting, L-PAS seems a feasible and suitable technique in order to induce plastic change within pain matrix in some UWS patients, allowing the production of "cortical" responses to painful stimuli, which are signs of at least partially ("focal") preserved consciousness. Cortico-thalamic plasticity could have also an important role in the emergence of pain perception as compared to other sensory modalities.