![]() This points to a somehow preserved awareness in the presence of reflexive motor output. Some individuals may have a dissociation of motor and cognitive function, i.e., they may retain some focal brain activations somehow sustaining conscious perception, despite the absence of integrated large-network processes known to sustain consciousness. The discovery of residual traces of awareness, covert awareness, and brain activity modulation in response to command and stimuli in some patients clinically labeled as UWS using advanced neuroimaging or electrophysiological techniques put in crisis the former assumption that patients with UWS are unable to perceive anything, including pain. Ĭonsistently with this premise, UWS patients should not perceive anything, including pain, even if they can show reflexive response to stimuli, including the nociceptive, but without any stimulus-related differentiation (i.e., purely reflexive behaviors). Therefore, MCS patients show inconsistent but reproducible or sustained and cognitively mediated behaviors associated with conscious awareness, differently from reflexive behavior as compared to UWS patients. The latter entity is a condition of severely altered consciousness in which minimal but definite behavioral evidence of self or environmental awareness is appreciable. The absence of response to commands or voluntary oriented movements in the presence of wakefulness is thus the main feature of UWS. Lastly, hypothalamic and brainstem function are preserved. Additionally, cycles of eye closure and eye-opening are preserved, giving the appearance of a sleep–wake cycle. The former entity is characterized by three (all necessary) clinical criteria: (i) no evidence of awareness of self or environment at any time (ii) no response to any stimuli suggesting purposeful behavior and (iii) no evidence of language comprehension or expression. PDOC mainly comprises unresponsive wakefulness syndrome (UWS, namely, vegetative state) and the minimally conscious state (MCS). Prolonged disorders of consciousness (i.e., more than 28 days) (PDOC) represent a possible evolution of coma, a condition following severe brain injury, characterized by a loss of wakefulness and awareness (mainly owing to a lesion in the ascending reticular system or diffuse (bi)hemispheric damage). To summarize, an accurate clinical and neurophysiological assessment should always be performed for a better understanding of pain perception neurophysiological underpinnings, a more precise differential diagnosis at the level of individual cases as well as group comparisons, and patient-tailored management. passive stimulation protocols), remain to be solved. Therefore, the significance of the neurophysiological approach to pain perception in PDOC seems to be clear, and despite some methodological caveats (including intensity of stimulation, multimodal paradigms, and active vs. This suggests that some patients with UWS may have residual brain functional connectivity supporting the somatosensory, affective, and cognitive aspects of pain processing (i.e., a conscious experience of the unpleasantness of pain), rather than only being able to show autonomic responses to potentially harmful stimuli. ![]() However, there are noteworthy exceptions, because some UWS patients show pain-related cortical activations that partially overlap those observed in MCS individuals. The available literature data suggest that patients with UWS show a more severe functional connectivity breakdown among the pain-related brain areas compared to individuals in MCS, pointing out that pain perception increases with the level of consciousness. In this scoping review, we dealt with the neurophysiological basis underpinning pain in PDOC, pointing out how pain perception assessment in these individuals might help in reducing the misdiagnosis rate. Conversely, multichannel electroencephalography (EEG) and laser-evoked potentials (LEPs) can be carried out quickly and are more adaptable to the clinical needs. However, advanced neuroimaging assessment can be challenging to conduct, and its findings are sometimes difficult to be interpreted. Therefore, pain perception has to be considered even in individuals with UWS. Advanced neuroimaging studies suggest some cortical activations even in patients with unresponsive wakefulness syndrome (UWS) compared to those with a minimally conscious state (MCS). Pain perception in individuals with prolonged disorders of consciousness (PDOC) is still a matter of debate.
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