Commentary: Cortical responses to salient nociceptive and not nociceptive stimuli in vegetative and minimal conscious state.

Abstract

We read with great interest the work by de Tommaso et al. (2015) assessing cortical responsiveness to nociceptive and multimodal sensory stimuli in patients affected by chronic disorders of consciousness (DOC). In their valuable work, the authors attempted to assign each patient to the most appropriate DOC category by using auditory, visual, somatosensory, and nociceptive laser stimuli. Interestingly, the motor responsiveness to nociceptive stimuli assessed through the Coma Recovery Scale-Revised and the Nociception Coma Scale-Revised correlated with each evoked response, but Laser Evoked Potentials (LEPs). The latter were recognizable in all of the patients, independently from the preservation of other sensory modalities and the motor responsiveness to nociceptive stimuli. Hence, LEP absence should not be considered as a demonstration of the inability to experience pain, since the preservation does not per se indicate a conscious pain perception in DOC (de Tommaso et al., 2015). However, it is to note that we should be aware in interpreting authors' findings since these are based on a very limited number of patients (i.e., only 4 MCS and 5 VS). Moreover, since the presence vs. absence of LEPs was based on a subjective visual identification of the event-related potential waveforms, the possibility of misinterpretations (mainly due to very low signal-to-noise ratio) should be taken into account.